Fracture analysis in the south-western Corinth rift (Greece) and implications on fault hydraulic behavior

Tectonophysics 426 (2006) 31 – 59 www.elsevier.com/locate/tecto

Fracture analysis in the south-western Corinth rift (Greece) and implications on fault hydraulic behavior Luca Micarelli ⁎, Isabelle Moretti, Manon Jaubert, Hakim Moulouel Institut Français du Pétrole, 1-4, av. de Bois Préau, 92852 Rueil Malmaison, France Accepted 7 February 2006 Available online 9 August 2006

Abstract This paper reviews the data concerning the fracture network and the hydraulic characteristics of faults in an active zone of the Gulf of Corinth. Pressure gap measured through fault planes shows that in this area the active normal faults (Aigion, Helike) act, at least temporarily and locally, as transversal seal. The analysis of the carbonate cements in the fractures on both the hangingwall and the footwall of the faults also suggests that they have acted as local seals during the whole fault zone evolution. However, the pressure and the characteristics of the water samples measured in the wells indicate that meteoric water circulates from the highest part of the relief to the coast, which means it goes through the fault zones. Field quantitative analysis and core studies from the AIG-10 well have been performed to define both regional and fault-related fracture networks. Then laboratory thin section observations have been done to recognize the different fault rocks characterizing the fault zone components. These two kinds of approach give information on the permeability characteristics of the fault zone. To synthesize the data, a schematic conceptual 3D fluid flow modeling has been performed taking into account fault zone permeability architecture, sedimentation, fluid flow, fault vertical offset and meteoric water influx, as well as compaction water flow. This modeling allows us to fit all the data with a model where the fault segments act as a seal whereas the relays between these segments allow for the regional flow from the Peloponnese topographic highs to the coast. © 2006 Elsevier B.V. All rights reserved. Keywords: Gulf of Corinth; Pirgaki fault; Helike fault; Aigion fault; Damage zone; Fault core; 3D fluid flow modeling

1. Introduction Fault zones are usually characterized by one or more relatively narrow zones of intense deformation, referred to as the fault core, surrounded by a wider zone of deformed rock, referred to as the damage zone, that grades outward into non-deformed (intact) host-rock or ⁎ Corresponding author. Now at: BEICIP-FRANLAB, 232, Av. Napoléon Bonaparte, BP 213, 92502 Rueil-Malmaison, France. E-mail address: [email protected] (L. Micarelli). 0040-1951/$ - see front matter © 2006 Elsevier B.V. All rights reserved. doi:10.1016/j.tecto.2006.02.022

protolith (e.g. Chester and Logan, 1986; Chester et al., 1993; Caine et al., 1996). Many authors have pointed out an inward intensification of fractures, subsidiary faults, cataclastic particle size reduction and mineral alteration toward the fault core (Linn et al., 2001; Du Bernard et al., 2002; Billi et al., 2003; Hammond and Evans, 2003; Micarelli et al., 2003), as well as a preferred orientation of subsidiary faults and fractures (Hesthammer et al., 2000; Cello et al., 2001; Micarelli et al., 2002a; Wilson et al., 2003). These features result in the structural domains of a fault zone acquiring different

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hydraulic behavior, that finally depends on the fault geometry and the strain history (e.g. Caine et al., 1996; Micarelli et al., 2005). Fault zone hydraulic behavior is a key issue for various domains of the earth sciences including seismic hazard, security of the water supply and waste storage and oil exploration. An intense activity of the scientific community is thus focused on this issue. An impressive data collection, including monitoring has begun, and numerous techniques have been developed to characterize the fault zones. The Corinth Rift Laboratory (CRL) has been installed in the south-western part of the Gulf of Corinth with the help of the European Community, to understand the relationships between faults, fluid flow and strain in a seismic zone (Moretti et al., 2002). Faults have been studied and monitored in an area approximately 30 × 30 km wide around the city of Aigion (Fig. 1). Surface captors, seismometers, strain meters, extensometers, tide-meters, tilt-meters are now working.

Fluids are monitored in terms of flow rate and chemistry in two selected aquifers (Pizzino et al., 2004). Two wells have been drilled and measurements have been done in surface as well as at various depths, especially with accelerometers and pore pressure transducers (Pitilakis et al., 2004). The drilling of the AIG-10 well (location in Fig. 1), intersecting the Aigion fault at 760 m in depth, allowed the recovery of a 100 m long core (Cornet et al., 2004a). Borehole images have been collected through the fault zone down to 1000 m (Daniel et al., 2004). An overview of the first results of the project can be found in the special issue of the C.R. Geoscience published by Cornet et al. (2004b). The present paper focuses on the fracture network, regional and near the Quaternary and active Pirgaki, Helike and Aigion fault zones, through carbonated series. A quantitative approach to the fracture spatial distribution and the characteristics of fracture networks has been achieved. In addition, thin section analyses allow us to

Fig. 1. Simplified geological map of the south-western sector of the Gulf of Corinth (based on Ghisetti et al., 2001; Micarelli et al., 2003; Moretti et al., 2003a). Active and Quaternary, approximately N100 striking fault zones are shown. Map also shows the main survey sites of this study, for scan area, scan line and microstructural sampling. Inset shows the location of the Gulf of Corinth and the zone modeled for the fluid flow.

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pinpoint the diagenetic evolution of the fault-related fractures and the role of cement precipitation on the permeability structure of the fault zones. The analytical work is based on surface data and core analyses and thus allows us to compare the results obtained using surface and/or subsurface data. The data collected by our partners from the CRL project concerning the pressure in the AIG-10 well as well as the characteristics of the water sampled in the Aigion well, and around, are rather paradoxical. The Aigion fault is parallel to the Helike fault, both act as barriers to fault-perpendicular fluid flow, whereas the water pressure excess and the very high flow rate encountered below the Aigion fault suggest a connection to the topographic highs of the Peloponnese, located south of the Helike fault (Fig. 1). We will propose an explanation based on a conceptual numerical 3D model of the fluid circulation through time in the area. 2. Geological setting 2.1. The Gulf of Corinth Crustal extension in continental Greece is currently active, in the general context of the back arc basin related to the Hellenic subduction. This process began in early Pliocene times (McKenzie, 1978; Roberts, 1996 among others) or even earlier (Miocene times; Jolivet et al., 1994; Armijo et al., 1996). The Quaternary high extensional strain rates have been accommodated by systems of E–W striking normal faults, which are responsible for the development of a series of sedimentary basins (e.g. Jackson and McKenzie, 1988; Roberts and Jackson, 1991; Doutsos and Poulimenos, 1992). In this framework, the Gulf of Corinth is the fastest extending graben in Greece and the most seismically active zone in Europe. The Gulf is a 105-km long, N100°E oriented elongated graben that cuts the N–S structural trend created by the older thrust nappes inherited from the Hellenides compression. The western Gulf of Corinth is extending north–south at a rate of 13–15 mm/year (Tselentis and Makropoulos, 1986; Billiris et al., 1991; Clarke et al., 1997; Davies et al., 1997; Briole et al., 2000) and shows up to 1.5 mm/year uplift rates of the southern shore since late Middle Pleistocene (Stewart, 1996; Stewart and Vita-Finzi, 1996). At the longitude of Aigion, seismological studies of recent earthquakes (Rigo et al., 1996; Bernard et al., 1997; Hatzfeld et al., 2000) indicate a major seismogenic zone at a depth of 4–10 km, dipping slightly to the north (Lyon-Caen et al., 2004; Latorre et al., 2004). The seismogenic zone could correspond to

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the Phyllades nappe, a heterogeneity inherited from the previous compressive phase, which acts as decollement level during the current extension (Le Pourhiet et al., 2004). In this context, the normal fault system in the Gulf, which consists of WNW-trending faults when the extension is N–S, could be explained by the reorganization of the stress near the decollement level (Mattioni et al., 2004). The main faults display dips between 55° and 80° and throws of up to 1 km (i.e. Poulimenos, 2000; Micarelli et al., 2003; Moretti et al., 2003a). The synrift depot center is located offshore in the central part of the current Gulf, where the sedimentary infilling reaches 2.5 km (Myriantis, 1984; Clément, 2000). The water depth is of 860 m (Brooks and Ferentinos, 1984). Due to the 60 m deep sea bottom in the Rio-Antirio pass connecting the Gulf to the Mediterranean Sea, the Gulf was periodically a lake during the late Quaternary. The last sea water invasion is dated around 12,000 yr (Perissotaris et al., 2000; Moretti et al., 2004). The northern shore of the Peloponnese and the eastern termination of the Gulf have undergone a strong uplift during the last 300,000 yr (between 405 and 250 kyr according to different authors) that has put in outcrop the first syn-rift deposits (Keraudren and Sorel, 1987; Collier et al., 1992). In general, these sediments consist of upper Pliocene–lower Pleistocene marine to lacustrine marls, capped by conglomeratic continental and marine–lacustrine Gilbert fan-delta sequences dated at 1 Myr (+/− 0.2) (Ori, 1989; Gawthorpe et al., 1994; Dart et al., 1994; Ghisetti et al., 2001; Moretti et al., 2003a). A protorift has been proposed by Ori (1989), coherently with the existence of the extensive strain pattern in the area since the Miocene. However, there is no dated sediment older than the upper Pliocene in the western part of the Gulf. Only on one site, eastward, near the Corinth city, Neogene sediments overlain by 4–3.5 Myr old andesites have been described (Collier and Dart, 1991), which may correspond to an early rifting, Aegean phase. 2.2. The Aigion area and the studied faults The studied area is located in the south-western part of the Gulf of Corinth (Fig. 1). The Aigion, Helike and Pirgaki faults are located respectively at about 0, 5 and 10 km south from the southern shoreline of the Gulf. The structural pattern is characterized by blocks bounded by sub-parallel faults; the blocks are not, or only very slightly tilted (Moretti et al., 2003a). The Aigion fault is trending N100° and dips 60° to the north. The fault plane is not exposed, the onshore part cutting through unconsolidated conglomerates. The

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related fault scarp, more than 100 m high, is nevertheless evident. The fault has been encountered at 760 m in the AIG-10 well proving that its dip angle is constant for at least the first 800 m. The offset is 180 +/− 30 m (Naville et al., 2004). Assuming a constant slip rate of about 3 mm/yr (De Martini et al., 2004), the age of the fault is about 50,000–60,000 yr (Micarelli et al., 2003). The last large earthquake causing surface ruptures occurred in 1995 (Koukouvelas and Doutsos, 1996), although the rupture in depth was located offshore northward (Bernard et al., 1997). The Aigion fault zone characteristics have been studied from the cores of the AIG-10 well. The Helike fault displays an average N100° strike direction and dips 55°–65° to the north, defining a wellmarked fault scarp, approximately 650 m high. In the studied area, striae show an average N025°/50° oriented slip vector. The length of the outcropping fault zone is about 25 km, but its total length is probably up to 35 km, because the fault continues below the sea towards the east (Fig. 1). The offset measured on seismic lines (Moretti and Naville, 2001) and deduced from displacement profiles (Micarelli et al., 2003) is about 650–800 m and the fault age may be estimated around 130,000 yr based on a slip rate of 5 mm/yr (Armijo et al., 1996; De Martini et al., 2004). Some other authors have proposed a lower slip rate, at least for the last 2000 yr (De Martini et al., 2004) that leads to an age of about 300,000 yr. The Helike fault is active, the last large earthquake surface rupture occurred in 1861 (Schmidt, 1879). The Pirgaki fault displays an average N095°–100° strike direction (Fig. 1) and striae striking about N020°– 022°. The fault zone crops out for at least 30 km. At several survey sites, we recognized a number of major sub-parallel fault planes in the same fault zone, with dip angles ranging between 40° and 70° to the north, which define an approximately 300 m high fault scarp. The fault zone marks the contact between the calcareous and flysch series of the Pindos alpine tectonic unit, and the marine/lacustrine marls (upper Pliocene–lower Pleistocene?) or conglomerates of the stacked Gilbert fandeltas (early Pleistocene; Malartre et al., 2004), but major planes between limestone and limestone are also present, as for instance described by Labaume et al. (2004). The fault activity was synchronous with deposition of the Gilbert-type fan-deltas (Ori, 1989; Poulimenos et al., 1989; Poulimenos, 1993; Gawthorpe et al., 1994; Dart et al., 1994; Ghisetti et al., 2001). A diffuse seismic activity occurred between the Pirgaki and Helike faults in 2001 with earthquake epicenters located at depths of 5–10 km (Lyon-Caen et al., 2004), suggesting that the Pirgaki fault is still active.

3. Field work Considerable research has been carried out to quantitatively define the characteristics of fracture networks affecting the fault cores, damage zones and, more generally, rock volumes. A general conclusion is that a wide variety of the fault zone attributes (i.e. cumulative fault displacement and length, fault-related fracture patterns, fragment size within fault rocks, etc.) display typical scaling relationships (e.g. Mandelbrot, 1983; Walsh and Watterson, 1992; Peacock and Sanderson, 1994; Barton and La Pointe, 1995; Cowie et al., 1996) that are indicative of a scale-free (fractal) distribution. These relationships can be described by power-laws of the type: NL = kL−D, where N is the number of attributes of a given size L or larger, k is a constant of proportionality, and D is the fractal dimension (Mandelbrot, 1983; Childs et al., 1990; Marrett and Allmendinger, 1992; Gauthier and Lake, 1993; Carter and Winter, 1995; Wojtal, 1996; Cello et al., 2001). For fracture and fault populations that follow fractal scaling laws, a log/ log diagram will define a straight line expressed as: log NL = D log (1 / L) + k, with D (the slope of the line) representing the fractal dimension of the given distribution, its degree of self similarity and geometrical complexity (e.g. Cello, 1997; Cello et al., 2001). 3.1. Methodology: how to define the fracture network and the characteristics of fractures Fracture analysis in the Aigion area is mostly based on the systematic study of fracture and fault characteristics in situ. It was mainly focused on mapping the geometry of each fault zone in detail, on assessing the kinematics, the spatial properties, and the typology of the fault-related fracture sets, and on investigating the regional fracture network. Micro-scale fracture analysis has also been performed to compare data from different scales. We used fractal statistics as a tool for defining the validity range within which the attributes of a fault zone may be considered as scale invariant, and quantitative structural analysis for assessing the overall properties of fault zones. To this aim, quantitative data on fabrics of the fault zones and surrounding areas (see Fig. 1) were collected by means of geological scan lines (one-dimensional techniques) and maps (two-dimensional techniques) as described in Appendix A. Oriented samples were systematically collected along and across the outcropping Pirgaki and Helike fault zones and surrounding areas, from Cretaceous limestones (Fig. 1). Samples relative to the Aigion fault come from the cores of the AIG-10 well. The orientation of

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bedding, subsidiary faults, fractures and veins were noted for each survey site or sample. Three oriented and mutually perpendicular thin sections were prepared from each sample. Thin sections have been analyzed under optical and cathodoluminescence (CL) microscopy in order to characterize the different fault-related features at various distances from the faults, to define the different calcite cements, the role of fractures on the permeability of the fault structural domains and the types of fault rocks associated with the studied faults. 3.2. Two-dimensional data: the fracture network spatial characteristics in the prerift sequence and in fault zones We carried out two-dimensional sampling by means of scan area analysis and box counting techniques (see Appendix A), with two main goals: i) at the meso-scale (outcrop scale), to define the characteristics of the regional background deformation affecting the protolith, where the studied faults developed; ii) at different scales, to compare the characteristics of different fracture networks (box counting analysis on different scale images). Scan area data at the outcrop scale (studied areas of approximately 1–2 m2; sampling location in Fig. 1) contain information on the fabrics of the protolith away from the main fault zones (Cello et al., 2001; Micarelli et al., 2002b). Fig. 2b shows a sample of scan area relative to the limestone series, from a sub-vertical outcrop. Orientation data coming from all the scan areas (Fig. 3) can be synthesized as follows, whereas data for individual faults will be shown in the next paragraphs. Bedding is mostly plunging at 10°–25° to the SE and secondarily to the NW, with main strike directions between N020° and N040° (Fig. 3a). This average NNE–SSW striking attitude is coherent with the anterift structure being controlled by N–S thrust structures. Extensional veins are mostly N060°–N075° striking and dip 60° to the NW. Sub-vertical, N–S oriented veins also exist (Fig. 3b). Two main other fracture sets have been observed: N025°–N045° and N145°–N155° striking (Fig. 3c). They correspond mostly to stylolites and shear fractures. Stylolites are related to layer parallel shortening. Their strikes are in agreement with the structural trends related to the Neogene fold and thrust belt building. Box counting curves relative to discontinuity trace maps at the outcrop scale (i.e. Fig. 2b) show power-law relationships, producing straight lines of slope ranging from 1.33 to 1.50 (mean value D = 1.44; correlation coefficients R2 N 0.99). This implies that the patterns studied show fractal geometry and self similarity char-

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acteristics. Their properties are thus comparable to other fracture networks at different scales of analysis (Ortega and Marrett, 2000). Box counting analysis has also been performed at geological map scale and on rock samples at both mesoand micro-scales (selected samples in Fig. 2; scanning resolution as shown in Appendix A). The trace-length population of the Aigion area has been analyzed using the map and the initial grid shown in Fig. 2a. This map stems from the geological maps published in Micarelli et al., 2003, Moretti et al., 2003a, Ghisetti and Vezzani, 2004, and from our field work. The analysis has been performed as shown in e.g. Walsh and Watterson, 1993; Cello et al., 2000; Poulimenos, 2000. The initial box is a rectangle approximately 25 km long and 20 km high. The best fit for the obtained curve produces a straight line of slope 1.44, which is the same value as we calculated for the outcrop-scale scan area analysis (average value). Possible errors associated with the map interpretation have been taken into account, but alternative interpretations produce variation of less than 2% on the calculated values. Fig. 2c and d show box counting analysis on discontinuity trace maps from both cut samples and thin sections. The slopes of the best-fit lines are of the same order of magnitude as those relative to outcrop and regional scales. This suggests that geological faults, mesoscopic structures, centimeter-scale discontinuities and micro-scale fractures have to be considered self-similar over two or three orders of magnitude in the analyzed area. Therefore, the value of D could be taken as representative for the regional discontinuity network away from the main fault zones in the studied area, at every observation scale, and relative to the analyzed limestone units constituting the host-rocks where the studied normal faults developed. In addition to the previous regional study, we also performed box counting analysis on samples coming from the fault zones, especially located at different distances from fault planes. Fig. 4a shows D values at cut sample and thin section scales, relative to the Pirgaki fault zone (see Section 3.3.). The highest values (average D = 1.66) characterize the fault rocks displaying foliated fabrics, in the core. D progressively decreases from the fault core to the damage zone. It returns to values of 1.45–1.48 at approximately 20–30 m away from the fault plane. These values are near to the D values characterizing the host-rock limestones, calculated away from the fault zones, as seen above. This peculiarity is mainly related to the geometric complexity and density of fracture patterns affecting the different structural domains. Fractures show smaller spacing and are more interconnected towards the fault plane.

36 L. Micarelli et al. / Tectonophysics 426 (2006) 31–59 Fig. 2. Regional fracture networks. Box counting analysis on discontinuity trace maps from: (a) the Quaternary fault trace map, (b) scan areas from a sub-vertical outcrop, with fracture orientation diagram; (c) cut samples (cm-scale) and (d) thin sections (mm-scale). The fracture trace maps and relative box counting curves are shown. “s” in the graphs is the size of the boxes used in the box counting analysis. See the text and Appendix A for explanations.

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Fig. 3. Orientation diagrams (Schmidt projection, lower hemisphere) displaying all data from two-dimensional, outcrop-scale scan area sampling. Projections of the poles to planes relative to: (a) bedding; (b) extensional veins and (c) other fractures, mostly stylolites and shear fractures.

Connectivity is a fundamental property of fracture populations with respect to fluid flow. It can be evaluated semi-quantitatively from image analysis of scan areas by assessing the degree of physical connection among fractures within a network (sketch in Fig. 4b). We performed this kind of analysis by representing the results in a triangle diagram, as described by Ortega and Marrett (2000). The ratio of the number of fractures which are isolated (type I), simply-connected (type II), or multiply-connected (type III) over the total number of fractures in the network may be shown. The triangle diagram in Fig. 4b, relative to the Pirgaki fault zone, shows that the degree of connectivity has a clear trend, at both meso- and micro scales. Fracture connectivity strongly increases from the damage zone to the fault core. Increases in both fractal dimension and connectivity suggest that the two parameters are likely to be related. A similar characteristic has been described by Micarelli et al. (2004) in the Aigion area, for the fracture networks outside fault zones, by studying outcrop-scale scan areas. The higher geometric complexity (causing the increase of the calculated D) and the increasing connectivity degree of fractures in the damage zones close to the fault planes could strongly modify the behavior of the different fault zone domains with respect to fluid flow. 3.3. The Pirgaki fault zone Available outcrops along the Pirgaki fault allow the complete study of the hangingwall, whereas the analysis of the footwall is generally limited to the first dm or cm below the fault plane. In fault rock descriptions we will follow the simplified classification proposed by Sibson (1977) and Sibson (1994). One-dimensional sampling

(scan line analysis) of the discontinuities along lines normal to the fault strike, allows us to define from a quantitative point of view the fault core, the fault damage zone and the protolith (Fig. 5a; frequency % /distance diagram relative to the total number of measured fractures N = 750). 3.3.1. Fault core The main fault plane is usually associated with a 2– 4 m thick core (Fig. 5a). Note that in this domain, the number of crossed discontinuities is strongly underestimated, because of the difficulty or impossibility of sampling the dense fracture network (lack of resolution). The Pirgaki fault core shows both random and foliated fabrics. Fault rocks displaying random fabric widely occur in the fault core. They consist mainly of cemented protocataclasite and cataclasite (Fig. 6a; sensu Sibson, 1977). Cataclasite fragments, ranging from tens of μm to 5 mm in diameter, consist of angular limestone, calcite and chert grains (Fig. 6a and c). Preferentially oriented shear fractures and pressure-solution surfaces, forming angles from 15° to 40° with the fault plane, are present (see sketch at the top of Fig. 6a). These are about 100– 300 μm wide and in places appear open (Fig. 6c). This system of fractures bound separated blocks of older cataclasite, which were re-involved during a later phase of cataclasite formation, without cement precipitation. Foliated fabric is only locally developed along the Pirgaki fault plane. It characterizes mainly ultracataclasites (Fig. 6b; sensu Sibson, 1977), consisting of calcite and limestone angular fragments and red-brown matrix. The foliation observed under an optical microscope is defined by a system of clay-rich and oxide-rich beds, with an average spacing 50–200 μm (Fig. 6d). Among

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Fig. 4. (a) Results of the box counting analysis of fracture networks on samples coming from the Pirgaki fault zone. Samples have been taken at difference distances from the fault plane. D (fractal dimension) values are shown for fracture networks at both cut sample and thin section scales. D values increase from the damage zone to the fault core. (b) Degree of connectivity of fracture networks within the limestone series across the Pirgaki fault zone. Connectivity increases from the damage zone to the fault core at both cut sample and thin section scales (wddz: weakly deformed damage zone; iddz: intensely deformed damage zone).

them, it is possible to recognize elongated aggregates or preferentially oriented alignments of fine-grained mineral grains sub-parallel to the sense of shear (calcite and

limestone fragments from tens to hundreds of μm in size) and mostly fibrous calcite (Fig. 6d). The clayand oxide-rich beds (forming systematically angles of

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Fig. 5. (a) Spatial distribution of fault-related fractures (frequency % versus the total number of measured fractures N = 750) across the Pirgaki hangingwall damage zone (site P2, location in Fig. 1), from which it is possible to quantitatively define the main fault zone components, i.e. core, intensely deformed damage zone (IDDZ) and weakly deformed damage zone (WDDZ). The dashed part of the curve is meaningless due to the lack of resolution in sampling. Fault rock position is reported in the lower bar. The curve relative to the frequency of open, N100–N120 striking, late fractures is also shown (dashed gray). It shows the frequency % for each distance class, on the total number of counted open fractures (N = 150). Orientation diagrams (Schmidt projection, lower hemisphere) of the poles to discontinuity planes affecting the damage zone: (b) bedding, (c) secondary fault planes, (d) shear and extensional fractures.

10°–20° with the fault plane; see sketch in Fig. 6b), related to pressure-solution and shear processes, are interpreted as R-surfaces of a Riedel's network. They cut older structures and elongate-shaped, calcite-rich fragments of older cataclasite, testifying to an older phase of cataclastic formation.

3.3.2. Fault damage zone Above the core, the next 14–18 m thick zone (Fig. 5a) consists of highly fractured bedrock without foliation fabrics, with some bands of cohesive breccia and incohesive gouge (sensu Sibson, 1977). It is affected by several secondary fault planes. This domain

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constitutes the hangingwall intensely deformed damage zone (IDDZ) that is usually delimited towards the north by another major fault plane. In the weakly deformed damage zone (WDDZ), about 40 m wide, the density of fractures and secondary fault planes decreases drastically and the bedding appears evident. The hangingwall fault zone width is estimated to be more than 50 m. Orientation data diagrams show the contour plots of the poles of discontinuities affecting the damage zone, (Fig. 5b, c, d; Schmidt projection, lower hemisphere). Bedding is mostly dipping to the NE and secondarily to the E (Fig. 5b). The average attitude is coherent with data relative to the regional background deformation coming from two-dimensional data (see Section 3.2. and Fig. 3a). The higher dip-angles and the NE dip direction could be related to drag deformation of limestone layers in the hangingwall of the fault. Secondary fault planes are sub-vertical and have strikes roughly parallel to the main fault plane (Fig. 5c). Fractures (mainly extensional and shear fractures) display a very clear clustering, with strike directions ranging between N100° and N120° (Fig. 5d). They are systematically perpendicular to the Pirgaki slip vector (N020°–022° oriented), and not to the fault dip direction (N335°–345°). Fig. 5a also displays the frequency/distance diagram relative to N100°–N120° striking fractures that are open and partially open (dashed gray line). It shows the frequency % for each distance class on the total number (N = 150) of open fractures measured along the scan line. The frequency of open fractures progressively increases within the damage zone towards the fault core. In particular, they are very abundant in the IDDZ, whereas the core is mainly characterized by cataclasite. However, it is important to note that these fractures are open in the WDDZ (Fig. 6e), but partially to completely cemented in the IDDZ (Fig. 6f). Cement consists of clear, nottwinned calcite that fills fractures and porosity. Several phases of calcite mineralization are recognized by cathodoluminescence microscopy (Fig. 6g), which suggests a well-developed fluid circulation in the damage zone and the progressive filling of fractures. The degree of cementation increases towards the fault core, which is usually well-cemented.

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This datum has to be coupled with those relative to the increase of both fractal dimension and fracture connectivity in the Pirgaki fault zone (see Section 3.2. and Fig. 4). The density and connectivity of open and partially open fractures increase from the WDDZ to the IDDZ and the fault core, whereas calcite cement completely fills fractures only in the fault core. 3.4. The Helike fault zone Available outcrops along the Helike fault allow for the complete analysis of the footwall fault zone. The hangingwall damage zone is rarely preserved and is largely constituted by conglomerate deposits (Gilbert fan-deltas bottom set deposits). In this paper we will focus on the fault zone architecture within limestone series. 3.4.1. Fault core The Heliki fault core is approximately 2.5 m thick (Fig. 7a). It consists of cataclasite, poorly cemented crush breccia, with bands of incohesive gouge (sensu Sibson, 1977). Cataclasite is cemented, matrix-supported (Fig. 8a, b), and displays a random fabric with fragments ranging mostly from tens of μm to 1–2 mm in diameter (Fig. 8c). The fragments consist of angular to sub-angular limestone and calcite grains. The matrix is commonly light brown-yellow in color and is made of very small calcareous elements. Blocks of wellcemented older cataclasite are involved within the more recent cataclasite (Fig. 8b), suggesting that several episodes of slip occurred within the fault core. The later cataclasite is affected by a closely-spaced system of veins, which cut all the other microstructures and therefore record the latest deformation process (Fig. 8a and c). Veins are totally or partially filled by clear, nottwinned, subhedral calcite (Fig. 8c). They are systematically sub-vertical and form at an angle of about 30° to the fault surface (see sketch at the top of Fig. 8a). In places, crush breccia (sensu Sibson, 1977) and highly fractured limestones constitute the fault plane (Fig. 8d). The angular limestone and calcite fragments composing these fault rocks have diameters between

Fig. 6. Pirgaki fault core. (a) Highly cemented protocataclasite and cataclasite displaying random fabric (cut sample; survey site P1). Sketch shows the orientation of the shear and pressure-solution surfaces compared to the fault plane. (b) Cataclasites and ultracataclasites displaying foliated fabric (cur sample; survey site P2). Sketch shows the orientation of the main microstructures compared to the fault plane. (c) Random fabric cataclasite (crossed polarized microphotograph; survey site P1), with random or preferentially oriented shear and pressure-solution fractures. (d) Foliated ultracataclasite: the foliation is defined by a dense system of clay-rich and oxide-rich beds (plain light microphotograph; survey site P2). Pirgaki damage zone. (e) Open fractures in the WDDZ (plain light microphotograph; survey site P2; brown: impregnation of the epoxy resin in pores; (f) partially filled fractures in the IDDZ. Last cement is clear, not-twinned calcite (plain light microphotographs; survey site P2; blue: impregnation of the epoxy resin in pores). (g) The last cement is dull- and yellow-luminescent (cathodoluminescence microphotograph).

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Fig. 7. (a) Spatial distribution of fault-related fractures (total number of measured fractures N = 1150) across the Helike footwall damage zone (site H5, location in Fig. 1). The dashed part of the curve is meaningless due to the lack of resolution in sampling. Fault rock position is reported in the lower bar. The curve relative to the frequency % of open, E–W striking, late fractures is also shown (dashed gray; total number of counted open fractures N = 194). Orientation diagrams (Schmidt projection, lower hemisphere) of the poles to discontinuity planes affecting the damage zone: (b) bedding, (c) extensional veins, (d) shear fractures.

50–300 μm and 5 mm. Extensional, mainly empty, subvertical microfractures are present (Fig. 8d), forming an angle of about 40° with the fault surface (see sketch in the top of Fig. 8d). The fractures cut the large calcareous fragments, suggesting that they are late and developed when the cataclasite was already cemented (Fig. 8d).

3.4.2. Fault damage zone The IDDZ is 7 m thick (9.5 m including the core; Fig. 7a; frequency %/distance diagram relative to the total number of measured fractures N = 1150), and contains a high percentage of fault-related fractures. Most fractures are nearly vertical and strike sub-parallel to the

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fault plane. In the WDDZ (approximately 22 m wide), the deformation in the limestone is localized within some major 50–150 cm wide shear zones, and along some secondary fault planes. The shear zones are characterized by 80° dipping shear planes, and 10°–20° dipping foliation planes, commonly re-using clay-rich interlayers. The density of subsidiary faults and fractures decreases progressively away from the core of the Helike fault to low, regional background levels at about 32 m from the plane, where most structures are not related to the fault. Orientation data diagrams show the contour plots of the poles of discontinuities, secondary faults and fractures affecting the damage zone (Fig. 7b, c, d; Schmidt projection, lower hemisphere). Bedding is plunging at 25°–50° to the E (Fig. 7b). This attitude is coherent with the ante-rift structure being controlled by N–S thrust structures. Extensional veins are mostly N090°–N100° striking and dip 60°–80° to the N. Also, roughly N–S oriented veins exist (Fig. 7c). Most shear fractures are sub-parallel to the Helike fault plane (N005°/60°; Fig. 7d). Other fracture sets exist, mainly N120°–N150° striking, nearly normal to the slip vector on the main fault plane (average orientation N025°/52°), as seen above also for the Pirgaki damage zone. The diagram frequency % versus distance from the fault plane, relative to open and partially open E–W fractures (total number N = 194), is shown in Fig. 7a (dashed gray line). These fractures are rare outside the damage zone and their frequency increases towards the IDDZ. Calcite cement is commonly present, but it rarely fills completely the fractures that show large voids (Fig. 8e). Cathodoluminescence microscopy highlights several generations of calcite cement (Fig. 8f) filling the fractures sub-parallel to the fault plane, which testifies that fluids easily circulate through the damage zone. This cement appears to strongly increase towards the fault plane, as seen also in the Pirgaki fault zone. 3.5. The Aigion fault zone The Aigion fault was drilled in 2002 in the frame of the European projects DGlab and 3F-Corinth. The synthesis of the well log can be found in Cornet et al. (2004a). The prerift sequence, consisting of limestones and radiolarites of the Olonos Pindos Unit, has been touched at 500 m. The coring started at 710 m and the fault has been cut through at 760 m. Below 781 m in depth, borehole images and water flow data highlight the presence of a high-permeability zone, possibly related to karst features. The well has been drilled up to 1000 m without coring, as the core recovery became

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very poor. A sketch of the main fault components deduced from a macroscopic description of the cores was published in Micarelli et al. (2003). The damage zone characteristics are very similar to those described in the Pirgaki and Helike faults from the field work. Description of deformation features in the hangingwall and footwall may be found in Moulouel (2004) and an analysis of the borehole images (UBI, FMI) in term of fracture network is presented in Daniel et al. (2004). In the following description, a trigonometric correction has been performed on depths measured in the well, to define the sizes of fault zone components perpendicularly to the fault. 3.5.1. Fault core An approximately 6 m thick lens of strongly sheared red clay derived from radiolarites is present in the footwall, just below the fault plane (Fig. 9a; Micarelli et al., 2003; Daniel et al., 2004). The first meter appears to be endured due to weak cementation and, with a cataclasite band in the limestones above the fault plane, constitutes the fault core that is 2–2.5 m thick (Fig. 9a). Because of the presence of this sheared clayey lens, which has been interpreted as due to smearing processes along the fault plane, the domain that has to be considered as impermeable is substantially wider than the simple fault core. Calcite cement, which is related to latest breccia formation processes in limestones, shows a typical orange zoned luminescence (OZL) under cathodoluminescence microscopy (Fig. 10, sample S52). It has been found also in the damage zone (below 743 m in depth) but is very rare. This cement increases towards the fault plane, and in the core it becomes very abundant (from 755 to 760 m in depth). The porosity is therefore strongly reduced near the fault plane. 3.5.2. Fault damage zone Above and below the sheared clayey band, cataclasites, protocataclasites (sensu Sibson, 1977) and fractured limestones complete the IDDZ, 3 m and 9 m thick respectively above and below the fault plane (Fig. 9a; frequency % /distance diagram relative to the total number of measured fractures N = 290). In the hangingwall, the upper part of the cataclasite band constituting the IDDZ in limestones, displays a high porosity due to the presence of fractures not completely filled by the OZL calcite. In the footwall, the IDDZ limestone cataclasite band (G in Fig. 9a) shows similar characteristics, but late calcite cement is substantially less abundant than in the hangingwall. The footwall fault rocks thus show a higher porosity than in the hangingwall. Moreover, the late cement displays the same color as the

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limestone host-rock under cathodoluminescence microscopy (Fig. 10, samples S61 and S63). The different colors of the calcite cement under CL microscopy in the hangingwall and the footwall, suggest a complete lack of fluid flow between the two compartments since the formation of the Aigion fault zone. According to macroand micro-structural data, the total width of the Aigion fault zone is 25 m (Fig. 9a). Fractures affecting the damage zone define three main orientation sets (Fig. 9b, c): N–S striking, inherited from the compression phases; NW–SE, corresponding to stylolites related to layer parallel shortening; late E–W striking, related to the current opening, as discussed in Daniel et al. (2004). Core and borehole images show that the late E–W fractures are partially open (Fig. 10, cut sample S32). Their frequency strictly defines the fault damage zone, being rare outside the damage zone and increasing towards the fault plane (Fig. 9a; dashed gray line, total number N = 42). Two types of calcite cement fill them: in the hangingwall, the first has the same color as the limestone host-rocks under cathodoluminescence microscopy, whereas the second displays a succession of three generations of calcite (non-luminescent NL, yellow-luminescent YL and orange luminescent OL; Fig. 10, samples S2 and S32; see also Moulouel, 2004). In the footwall both cements have the same color as the limestone hostrocks. Finally, the footwall is characterized by little precipitation of late, red-luminescent, calcite cement. Pressure excesses encountered when crossing the fault, the presence of the high-permeability zone described above, as well as numerical modeling (Frima et al., 2005), suggest, on the contrary, dissolution of the carbonate by the circulating water. 3.6. Discussions and conclusions on the field work 3.6.1. Fractal statistics The recognition of the scale-invariance characteristics of a fracture network is prerequisite to the comparison of fracture properties observed at different scales. Micro- and macro-fractures could represent different

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size fraction of the same fracture sets, and consequently have linked attributes (Ortega and Marrett, 2000). For example, fracture orientation remains roughly constant through different scales and by using different sampling methods (compare orientation data relative to outcropscale scan areas, scan lines, well coring, cut samples…). Fractal analysis on fracture networks at different scales (km- to mm-scales) in the Aigion area suggests that all the studied patterns are self-similar over two or three orders of magnitude (i.e. refer to Fig. 2). This allowed us to compare the properties of a fracture pattern with those relative to other fracture networks at different scales of analysis. However, some attributes, such as connectivity and cementation of fractures, show scale dependency. 3.6.2. Orientation data Regional features affecting the protolith have been defined by outcrop-scale scan area analysis located away from fault zones. Scan lines across the fault zones, instead, contain information on both regional features and fault-related discontinuities. Bedding is roughly plunging to the E in all the studied datasets (Figs. 3a, 5b, 7b, 9b)). This orientation is coherent with the ante-rift structures controlled by N–S thrusts. NW–SE and roughly NE–SW fractures, corresponding mostly to stylolites and shear fractures, and N–S extensional veins, are regional features that have been recognized by both scan area analysis and the study of the AIG-10 cores (Figs. 3 and 9; see also Daniel et al., 2004; Moulouel, 2004). Data coming from natural outcrops are thus coherent with data coming from core analysis. This suggests that the study ofnatural outcrops could complete, or even replace missing subsurface data (i.e. from wells) in characterizing and modeling fractured rock volumes, such as fractured reservoirs. Data sampled across the Pirgaki, Helike and Aigion fault zones (by scan lines and core analysis) suggest that most of the studied fractures can be interpreted as second-order features related to the growth of the faults. In particular, data show a clustering and most fractures are perpendicular to the slip vectors measured on the main fault planes, and not to the fault dip directions (refer to Figs. 5d and 7d). Thus, the horizontal

Fig. 8. Helike fault core. (a) Cemented cataclasite displaying a closely-spaced system of veins, cutting all the other microstructures (cut sample, survey site H3). Sketch shows the orientation of the main microstructures compared to the fault plane. (b) Blocks of older, highly cemented cataclasite involved within the more recent core (cut sample; survey site H3). (c) Contact between an older cataclasite block and the more recent cataclasite. Newly formed cataclasite displays a system of preferentially oriented veins (see sketch in Fig. 11a), totally or partially filled by subhedral calcite (plain light microphotograph; blue is the impregnation of the epoxy resin in pores). (d) Fine crush breccia and highly fractured limestones (cut sample, survey site H4), affected by a system of sub-vertical microfractures (see the sketch in the top). Helike damage zone. (e) Partially open fractures IDDZ (survey site H5; plain light microphotographs; blue: impregnation of the epoxy resin in pores). (f) Late, E–W fractures are filled by several generations of calcite, recognized under cathodoluminescence microscopy.

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component of the motion on the main fault plane strongly influences the orientation of related minor features within the fault zone. 3.6.3. Damage zone and fault core widths Measurements of the fault zone component sizes are fundamental for validating the coherence between the studied fault attributes and the fault zone parameters used in the modeling (see Section 5). Concerning the Pirgaki and Helike faults, we suppose a rough symmetry of the hangingwall and footwall damage zone sizes, by comparison with the AIG-10 well cores from the Aigion fault zone. This displays an overall symmetric damage zone size (Fig. 9a; Micarelli et al., 2003; Moretti et al., 2003b). Taking into account this approximation, across the Pirgaki fault the total fault zone width is estimated to more than 100 m. The Helike fault zone is estimated to be 60–70 m wide. The Aigion fault zone width is 25 m. The fault cores have similar sizes (ranging between 2 and 4 m; Figs. 5a, 7a, 9a)). The Pirgaki and Helike fault display similar offsets (between 650 and 1000 m; Micarelli et al., 2003), whereas the throw of the Aigion fault is 180 +/− 30 m (Naville et al., 2004). Even if the relationships between damage zone width and fault offset is still debated (e.g. Knott et al., 1996; Fossen and Rornes, 1996; Vermilye and Scholz, 1998; Shipton and Cowie, 2001), the widths of the studied fault zones seem to be related to the fault offset, within the same limestone lithology. 3.6.4. Fracture connectivity and permeability structure of fault zones In the studied fault zones, fractures affecting the fault core are drastically more connected than those in the WDDZ (Fig. 4b). We have not presented data concerning fracture networks outside fault zones, but probably the connectivity is significantly lower, as shown by Ortega and Marrett (2000) and Micarelli et al. (2004) for fractured rocks not affected by major faults. The semiquantitative approach used in the present work takes into account the proportion of fractures connected in the network but does not solve the scale dependency problem of fracture connectivity (Laubach, 1992). Therefore, it does allow comparisons of fracture network connectivity at a selected observation scale. However, Fig. 4

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shows connectivity data at two different scales (cut sample and thin section) for each sample, corresponding to a given distance from the fault plane. The two data sets have very similar trends. We can thus assess that, in the analyzed fault zones, the fracture connectivity degree increases from the WDDZ to the IDDZ and the fault core at different study scales. The used method ignores the effects that cementation and dissolution can have on fracture connectivity. Nevertheless, the presence of cements filling the fractures increases from the damage zone to the fault core that appears well-cemented. In particular in the WDDZ, many fractures, up to 20 mm wide, are open and empty, as recognized mainly in the AIG-10 cores (Figs. 9a, 10b, sample S32). Large fractures and wide connections might need a longer time to be completely filled, as also shown by numerical modeling (Frima et al., 2005). This fracture network defines a high-permeability zone that consists of highly fractured limestones in the damage zone and an “open” cataclasite, in places developing in the damage zone–core transition and the first cm of the core. The high connectivity (highlighted by high D values, refer to Fig. 4a) of fracture networks modifies the rock behavior with respect to fluid flow, causes the development of open geodes, and may favor the formation of tectonic proto-breccia and its evolution to cataclasite towards the fault plane (e.g. Billi et al., 2003). 4. Water flow and pressure: the data During the drilling of the AIG-10 well, the artesian pressure was 10 bars below the fault, and 4–5 bars above. The flow was of 50 m3/h during the three day long pumping test (Giurgea et al., 2004) on the lower part of the well. There was no casing below 700 m, but the water flow was very low down to the fault at 760 m in depth. Below the fault, borehole images suggest the presence of high-permeability zones (possibly karstrelated). The eruptive water flow was even higher (500 m3/h) few months later, when the well were reopened to install new captors (Cornet et al., 2004a). The measured pressure gap suggests that the fault plane locally acts as a transverse seal able to support several bars of ΔP. Production tests were performed during the drilling when aquifers were found (Giurgea et al., 2004). Three

Fig. 9. (a) Spatial distribution of fault-related fractures (total number of measured fractures N = 290) across the Aigion fault zone from the analysis of the AIG-10 cores. Fault rock position is reported in the lower bar. The curve relative to the frequency of late, open, E–W striking fractures is also shown (dashed gray; total number of counted open fractures N = 42). Orientation diagrams (Schmidt projection, lower hemisphere) of the poles to planes interpreted on borehole images, from Daniel et al. (2004), modified. (b) Poles above 744 m depth; (c) poles between 744 m and the Aigion fault. Bedding surfaces and E–W, NW–SE, N–S fractures are shown.

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Fig. 11. Modeling of the fluid circulation in a relay between two fault segments in the hypothesis of the existence of a high-permeability carrier bed (in green color) below a seal (in yellow), affected by low transversal permeability faults (represented in red). The block is 10 km in length × 10 km in width. The fault offset is 600 m. (a) Final 3D geometry of the area. (b) Present day fluid flow at the top of the high-permeability carrier bed. Black lines represent the vector of the water flow. (c) Stream flow at the top of the carrier bed (white arrows).

of them were located between 0 and 250 m, in gravels and conglomerates. Since the first syn-rift facies, probably corresponding to the distal part of the Gilbert fandeltas, are rather shaly in the area, there is no aquifer in these series. In the radiolarites, constituting the upper part of the pre-rift sequence, the flow is likely to be very low. In the carbonate, at 740 m, a production test has been done indicating a flow of 0.68 m3/h. The hydrochemical results of the 3 pumping tests, at 250 m (syn-rift conglomerates), 740 m (pre-rift limestone) and below the fault, have shown that the three waters are different (Giurgea et al., 2004). In the first

pumping test the water contains 500 meq/l of Na+, 580 meq/l of Cl−, 108 meq/l of Mg2+, and lower quantity of other ions; in the second pumping test the water contains 6.7 meq/l of Na+, 2 meq/l of Cl−, 5.6 meq/l of HCO3− ; in the third pumping test water contains 11.9 meq/l of Na+, 11.0 meq/l of HCO3−, and lower quantity of other ions. Similarly, hydrogeological data from the Helike fault also suggest that the fault plane acts as a local transverse seal. Farmers and industry produce water from various aquifers in the footwall series, vertically sealed by the fault. At least three artesian wells in the Selinous river

Fig. 10. Aigion fault zone: data from analysis of the AIG-10 cores done between 708 and 800 m depth. The fault has been encountered at 760 m. (a) Schematic diagram showing the different structural domains that have been defined based on a macroscopic description (Micarelli et al., 2003) and confirmed by thin section analyses. (b) Selected samples from the fault zone components: S2: late veins displaying two types of infilling, (i) red luminescent (RL) and (ii) non-luminescent–yellow luminescent–orange luminescent (NL–YL–OL; horizontal plain light and cathodoluminescence microphotographs); S32: late E–W open fractures (core cut sample and cathodoluminescence microphotograph); S52: NL–YL cements, and orange zoned luminescent (OZL) latest breccia-related cement (cathodoluminescence microphotograph); S61: latest open fracture cutting older structures (blue is the impregnation of the epoxy resin). The different cement generations show the same cathodoluminescence color (plain light and cathodoluminescence microphotographs); S63: latest cement shows the same color than the host-rock (cathodoluminescence microphotograph).

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valley are producing water from the limestone below the fault plane. These data confirm the optical and CL microscopy observations on the well-cemented fault cores characterizing all the studied faults, as seen above (Section 3). 5. Modeling 5.1. The paradox The gap in pressure, the different water signatures and the high fluid flow below the fault plane suggest that the Aigion and Helike faults act as transverse seals. Thin sections analysis highlights the existence of well-cemented impermeable fault cores. In particular in the Aigion fault, the migration pathway between the hangingwall and footwall is likely to have been closed since the beginning of the fault growth. Therefore the question is how to explain the overpressure and the flow rate measured below the Aigion fault. The topography between the Helike and Aigion faults does not exceed 200 m, and there is neither hydrocarbon generation nor fast sedimentation rate to produce overpressures below the Aigion fault. This means that the water flow is due to a hydraulic connection with a higher point. The Peloponnese is far from being flat. The topography highs reach 700 m between the Helike and Pirgaki faults, 1777 m in Mt. Klokos south from the Pirgaki fault (Fig. 1) and finally 2338 m in Mt. Helmos near Kalabrita at about 16 km south from the Pirgaki fault. From a static point of view the hydraulic load H is p linked to the pressure by: H ¼ qg þ z where z is the elevation, g the gravity constant and ρ the water density and p the water pressure. Currently, the water circulating through the layers is mainly rain water (Pizzino et al., 2004). There is no more deposition and therefore no more compaction in the offshore part of the model (to create overpressure), southward from the Aigion fault. The Darcy flow is: m ¼ −Kd ddHl where K is the hydraulic conductivity, and dH/dl the hydraulic gradient. The hydraulic conductivity is related to the intrinsic permeability k: K ¼ kdqdg=l with ρ fluid density, g gravity and μ fluid viscosity.

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The presented data suggest thus a regional hydraulic connection between the relief and the coastline. Two main possibilities exist to explain the paradox. The first relates the measured ΔP to fault permeability changes with time. However, thin section analysis on cataclasites and calcite veins suggests permanently different hydraulic systems, since the Aigion fault exists, between its two sides. The second possibility, based on the fact that faults consist of various segments, considers the full 3D system. The relays between various fault segments (Fig. 11a) are known to influence in surface the river geometry and the delta location (e.g. Collier and Gawthorpe, 1995), but also the migration pathway at depth. We tested this second hypothesis. In the studied area, Pizzino et al. (2004), by the analysis of more than 50 samples from various aquifers and artesian wells, emphasize the specific role played by the relays between the fault segments on the groundwater circulation. In particular, the CO2 concentration is abnormally high near the extremity of the different segments of the Helike and Aigion faults (see Fig. 1 in Pizzino et al., 2004). To study the influence of the relays between fault segments on regional fluid flow, the use of a 2D model, even though powerful, is hence meaningless. Therefore we used the 3D-TEMISPACK® software in order to model the 3D water flow in the area (see Appendix B). This industrial software is usually used in the oil exploration business to study the basin evolution, including pressure evolution, subsidence, erosion, sedimentation, and compaction. All processes are described as transient. It is not a classical software for water circulation in the ground, in which the geometries are constant but the carrier bed are much better defined. A first simple run was done on the single relay shown in Fig. 11a. The faults are represented by a low-permeability zone (range of permeability corresponding to compact shale), and do not show damage zone around fault cores. The faults affect a succession consisting of a high-permeability carrier bed below a lower-permeability seal. The water flow follows the layer dips from the topographically highest points to the faults; then it runs along the faults to the relay and continues to go down by passing through this zone (Fig. 11b). We then applied this concept to the modeling of the regional fluid flow near Aigion.

Fig. 12. 3D volumetric model used in the fluid flow modeling. The faults (in red) have been represented with a vertical dip to fit with the software functionalities. The color code is based on various facies (age + lithology), the carbonated pre-rift sequence appears in green, the synrift in yellow (conglomerate + Gilbert delta) and blue (marine terrace for the light blue and recent alluvial deposit for the dark one). (a) View of the model (present day geometry), from the west, looking eastward. (b) Cross section through the previous model. (c) Zoom on the mesh around the faults; transversally, each fault is represented by 4 nodes (3 cells).

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Fig. 13. Fluid flow through the model. (a) Water flow (black) and stream lines (red) at the top of the pre-rift sequence. In the studied area the Helike and Aigion faults are segmented. (b) Cross section. (c) Computed overpressures near the Aigion fault at 800 m depth. The cells are approximately at the same depth. Since the fault is vertical in the model, the computed pressure evolution cannot be displayed on a vertical line that could be compared to the well.

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5.2. Model The studied area is oriented N015° in order to keep one of the axes parallel to the faults (see location in Fig. 1). This choice allows the anisotropies of the material properties to be defined along the axis, and the fault core and damage zone properties to be better described within the regular cells imposed by the software. The studied 3D block is shown in Fig. 12a. The geometry and the lithologies are based on our regional set of data. A special attention has been given to the relief and to the fault segment lengths. The syn-rift sequence consists of conglomerate, shale and sand, as described by Ori (1989) and Ghisetti et al. (2001). The pre-rift series consists of mainly limestones and radiolarites. Since we have no measurement, the porosity and permeability are deduced from lithology and depth. It is not our objective to model the subsidence and fluid flow from the Mesozoic up to now. However, in order to obtain a realistic porosity in the Mesozoic sediments, we have to take into account the burial due to the Hellenic compression. To schematically do this, the modeling has been started at 120 Myr before present, and first a Tertiary sedimentary load, then erosion, before the beginning of the Quaternary rifting phase, have been imposed on the Mesozoic deposits. The fault zones are represented by 3 cells: the fault core and two damage zones in the hanging and footwall, respectively (Fig. 12c). Due to the scale, the damage zones, corresponding to narrow cells, are very poorly visible on the global view (Fig. 12a) and on the cross-section (Fig. 12b). According to field and core observations, a low permeability (∼ 10− 20 m2) has been assigned to the fault rocks in the core, whereas the damage zones have a higher permeability (∼ 10− 14 m2) than the surrounding carbonates (∼ 10− 18 m2). Porosity measured in the limestone is about 1%, therefore permeability is mainly due to the fracture network characteristics. As seen above (see (Figs. 4, 5a, 7a, 9a)), fracture connectivity and density of open fractures increase towards the fault core, whereas calcite cement strongly seals fault cores. In TEMISPACK, porosity and permeability are obviously depth- and pressure-dependent in the block; the given values are a rough average. Due to the sizes of the cells (few tens of meters), the average permeability value is in general smaller than the laboratory values measured on single, small samples. In general, the permeability shows anisotropies, due to the bedding. We have used Kh = 10 ⁎ Kv (Kh horizontal and Kv vertical permeabilities) in the coarse sediments, as the syn-rift conglomerate, and Kh = 100 ⁎ Kv in the pre-rift sediments and the shales.

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Some studies (e.g. Curewitz and Karson, 1997) show that fault tips and fault relays may have increased permeability. Besides data from the Aigion area (Pizzino et al., 2004) seems to confirm this characteristic. We do not take into account this increase in the schematic numerical model presented here. However, such a higher permeability should enhance the role played by the fault relays on fluid flow. 5.3. Flow boundary conditions The supposed initial conditions are under hydraulic pressures, which means that the water table is everywhere near the surface. For the lateral sides of the model (east and west) the border is hydraulically pressured. The thermal boundary conditions are: imposed temperatures at the top, 5 °C offshore, 15 °C onshore; imposed heat flow at the bottom (60 mW/m2); adiabatic borders in the lateral sides (north, south, east, west) of the 3D models. 5.4. Results Fig. 13a shows the water flow at the top of the pre-rift sequence. The black arrows represent the water flow and the red lines highlight the stream lines. In the lack of barrier, the water flows preferentially parallel to the bedding. When a low-permeability fault is encountered, the flow goes round the fault and passes in the relay. As a result, the main flow goes down from the topographic highs of the Peloponnese to the Gulf of Corinth northward. When the water encounters a transversally impermeable fault, it flows parallel to the fault eastward or westward up to the next relay. In the model, at the level of the AIG-10 well, the flow goes eastward on the footwall of the Aigion fault (Fig. 13a). This direction is induced by the boundary conditions (i.e. no transverse flow through the lateral border) and the fact that the Aigion fault segment, which has been drilled, touches the border of our model. Otherwise, eastward or westward fluid flows are possible on the area. At this stage of the project, there is no data to define the direction of the flow in the high-permeability zone below the Aigion fault. 5.4.1. Pressure around the Aigion fault During the drilling of the AIG-10 well, the measured pressure was 5 bars in the hangingwall of the Aigion fault and 10 bars in its footwall. Numerous runs have been done, with different permeability values and anisotropies of permeability to fit these data. Without a highpermeability zone in the footwall of the fault, it was

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impossible to get the overpressure measured under the faults. Fig. 13c shows one of the obtained best fit. The overpressure is 10.8 bars in the high-permeability zone below the fault. The overpressure is even higher in the fault core due to the very low permeability, but we have no data at this depth. There is a slight mismatching between the pressure measured in the hangingwall (5 bars) and that in the model (1.6 bars). In the model, under hydraulic boundary conditions, the area between the Aigion fault and the external border is roughly hydrostatic. By modeling a larger zone and by taking into account other faults, northward from the Aigion one, overpressure may exist in this area. A parameter that can be useful to test the validity of the model and to calibrate the permeability field is the travel time, which means the age of the meteoric water sampled in the AIG-10 well. Unfortunately these data are not yet available. 5.4.2. Overpressure below the fault: origin of the water Chemical analyses have shown that the water is essentially meteoric (Giurgea et al., 2004; Pizzino et al., 2004. The geographical origin of the water is an important datum to constrain the system, in the aim to fit the overpressure and flow data and then to quantify the changes in permeability due to diagenesis. Due to the topography and the resulting hydraulic load, it is unlikely to find sea water infiltrations south of the Aigion fault. However, the hangingwall area with no overpressure may be invaded by sea water since it is very nearby the sea. The previous runs have shown that in the Aigion fault footwall the overpressure may be explained by the topography elevation and a water flow from the south to the north. In the area taken into consideration (only 18 km wide), the Pirgaki fault appears rather continuous (Fig. 1). However, at a larger scale, and/or taking into account more details, the fault is not continuous, and another set of runs has been done considering a segmented fault that allows migration from the topography highs south from the Pirgaki fault towards the Aigion area. The results are similar to those obtained with a hydraulically-closed Pirgaki fault, but the overpressure in the high-permeability zone is higher: 11.5 bars. This low difference does not seem to be very conclusive to either preclude or prove the hydraulic connection between the southern topographic highs and the footwall of the Aigion fault. 6. Conclusion In the Aigion area, quantitative and microstructural analyses on natural outcropping fracture networks have

been integrated with the analysis of the cores coming from the AIG-10 well. Surface and subsurface data appear to be coherent, and allowed us to distinguish the discontinuities characterizing the regional fracture network from the fractures related to the active roughly E–W oriented normal faults. E–W trending, fault-parallel fractures characterize the fault damage zones. Their density and connectivity, which have been estimated by using semi-quantitative methods at different scales, increase towards the fault cores. The high connectivity of fractures modifies the rock behavior with respect to fluid flow and is likely to create migration pathways. On the other hand, calcite cement fills the fractures, and increases from the damage zone to the fault core. Fault cores, thus, appear impermeable, due to the presence of calcite cement and/or to the smearing of low-permeability material (clay, clayey radiolarites…). According to these data, the studied fault zones, affecting low-permeability limestones, are characterized by cemented cores acting as transverse seals, and surrounded on both sides by high-permeability damage zones, affected by open and highly connected fractures. The fault zone widths have been estimated at approximately 100 m, 60–70 m and 25 m respectively for the Pirgaki, Helike and Aigion faults. They are probably related to the fault offsets, within the same limestone lithology. Hydraulic data, coming from water-producing well, show that fluid circulation is well-developed below the Aigion and Helike faults. The overpressures measured below the Aigion fault are not compatible with an isolated hydraulic domain between the Aigion and the Helike faults. Therefore, the hypothesis of a water flow circulating through the relays between the various segments of the faults has been quantitatively tested, in order to explain the pressure difference between the hanging and footwall of the Aigion fault. According to the available data, we took into account fault zones acting as transverse impermeable features. The modeling systematically shows that fluids flow parallel to the main fault segments, in their footwall, up to their tips. Then, they cross the fault zone in the relay between fault segments. These results are coherent with the data relative to the studied outcropping fault zones, and explain the measured overpressures. Nevertheless, our results are not conclusive on the following points: (1) the hydraulic connection between the Aigion fault footwall and the highest points in the Peloponnese.

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The topography between the Pirgaki fault and the seashore is high enough to explain the overpressure below the Aigion fault. This means that the migration pathway of the water found below the Aigion fault could be less than 15 km long, from the land of rainwater infiltration to the Aigion fault; (2) the time required by the circulating fluids to migrate from the Pirgaki to the Aigion fault zone. We are waiting for water dating to precise this part of the model. Acknowledgments This study has been carried out thanks to the EEC project DG-Lab and 3F-Corinth for the data acquisition and thanks to the Groupement de Recherche GDR-Corinthe for the modeling and thin section analyses. We thank Jean Marc Daniel, Sandra Tenchine, Claudio Delle Piane and Stephanie Eyssautier-Chuine who also participate to the study of the Corinth fracture network within the Institut Français du Pétrole. We are grateful to two anonymous reviewers for their very constructive comments. Appendix A. Fracture analysis by scan line and map techniques One-dimensional sampling (scan line analysis) collects data of a fracture network cropping out along a line normal to the fault strike, to infer power-law distributions of fracture and characterize the main fault components. Along this line, distances from the origin and orientation data of each discontinuity and fabric element are measured; their morphologic and geologic characteristics (such as spacing, filling, roughness, geologic type, etc.) are evaluated. Before quantitative/ fractal statistics, a trigonometric Terzaghi correction is performed on the collected data to project them on a plane perpendicular to the fault strike. The spacing measurement ranged from 1 mm to 100 cm and the discontinuities were recovered and counted from the established distance of 1 m from the outcrop, for collecting data at the same resolution. Possible sampling errors are less than 10%, at least in a range of validity from 2–3 mm to 80 cm, and would be related to changes in dip and strike of the fractures with respect to the trend of the sampling line (Poulimenos, 2000). One-dimensional data of this type avoid truncation (Heffer and Bevan, 1990) and censoring (Jackson and Sanderson, 1992) problems, respectively resulting from incomplete sampling of a population and underestimation of large-

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scale values of a sample (Walsh et al., 1994; Pickering et al., 1995; Needham et al., 1996). Anyway, these kinds of problems are indicated where they arise in plotted data. Two-dimensional sampling (scan area analysis) allows for the study of the spatial distribution of discontinuities in a specified area. Preferably, it is made away from fault zones, with the aim of characterizing the regional, background discontinuity network. However, we have also applied this technique in fault rock samples, at both cut sample- and micro-scale, in order to compare the discontinuity patterns relative to the faults under study. On the outcrop, we carried out measurements on both bedding surfaces and sub-vertical surfaces (cutting bedding surfaces with a high angle; see Fig. 2b). The studied areas had sizes of 1–2 m2 and all discontinuities countable at a distance of approximately 1 m have been taken into account and measured for trace-length population diagrams. At the cut-sample scale, the studied areas had sizes of approximately 50–100 cm2 and we marked all fractures countable on polished cut sample surfaces. At the micro-scale, the studied areas had sizes of 1–2 cm2 and all fractures countable at a microscopy enlargement of about 20–30 times have been put in the analysis. The length measurements definitely have some errors of truncation and censoring, due to the limited size of scanned areas and to the limited resolution for small objects. Scan area data refer to the same parameters of scan lines, but away from the fault zone, and provide a discontinuity trace map from which fractal dimension of fabric elements can be derived, by means of the “box counting method” (Barton and Larsen, 1985; Walsh and Watterson, 1993). The procedure is to cover the analyzed discontinuity network by a sequence of grids, then to count the number of occupied boxes as a function of the box size (Hirata, 1989). After the first calculation, the process is repeated many times using boxes with smaller sizes (conventionally, the box side is halved each time). Box counting should be performed over as wide a range of box sizes as possible, but the relevant part of the curve is that corresponding to box sizes between those of the largest and smallest discontinuity or fracture spacing (Walsh and Watterson, 1993; Poulimenos, 2000). Therefore, the initial boxes have been chosen as a function of the size of analyzed patterns, at all analyzed scales. We used the same program (HarFA 4.0 — Harmonic and Fractal Image Analyzer, by Nezadal, M. and Zmeskal, O.) for every sample at all scales, which allows eventual comparisons.

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Appendix B. Fluid flow modeling with TEMISPACK Numerical model TEMISPACK is an IFP software marketed by the BEICIP. Studies can be done in 2D (Doligez et al., 1987, Ungerer, 1990) and 3D (Schneider et al., 2000). The core of the basin modeler is composed of five principal modules, fully coupled: (1) backstripping module; (2) mechanical compaction module to compute the water flow, the overpressure and the final porosity of each bed; (3) thermal module to compute the history of subsurface data, both conductive and convective flow are considered; (4) kerogen maturity module based on kinetic reactions; (5) HC migration module, based on a 2-phase flow (HC + water) Darcy equation for the 3D version, that computed the mass of HC displaced across the mesh in response to driving force: buoyancy, gradients of hydraulic pressure head and capillary forces. Assumptions Temperatures are calculated with a constant basal heat flow and surface temperatures depending on the elevation. The choice of a constant basal heat flow since the Cretaceous in the area is not appropriate but without importance, because we are not interested in the maturation of any organic material. In the case of topographic relief, hydrostatic conditions are applied by default. This means that in the Peloponnese the recharge is considered abundant enough to ensure locally the hydrostatic equilibrium of the area, the water head being equal to the elevation. As a result, dynamic flow occurs and it is computed by the program between the highest part (the mountains of the Peloponnese) and the lowest part (under the Corinth Gulf). The left and right borders are hydrostatic in the presented results. Other runs have been done with a closed hydraulic border on the northern border of the studied area. Since the model does not extend down to the deepest part of the Gulf of Corinth, the hydraulic choice is more realistic and has been retained for the final models. Faults: geometry and characteristics The current version of TEMISPACK does not allow for horizontal displacement. Only vertical movements (sedimentation, compaction, erosion, uplift) can be modeled. Anisotropy of the properties (porosity, permeability) is defined parallel to the cell borders, i.e. vertically and parallel to the layers. As a result, the faults are considered as vertical and the offset defined as a gap in the subsidence rate between the hangingwall and the footwall. To have a better definition of the fault core and damage zones, we thus made the modeling on a block with one of the

horizontal directions parallel to the faults, approximately N100° striking. Warning TEMISPACK is a finite element code, which means that the computed values are average values for the cells. For instance, water flow values computed by the program are average values in the carrier bed. Using this flow, it is difficult to compare the velocity and travel time of the water in the system with the data collected on the field. The computed values are highly dependent on the thickness of the defined carrier bed and therefore a high-resolution mesh should have to be defined to obtain meaningful values. The fault core and the damage zones have to be at least one cell thick. As a result, they are thicker than in the reality, especially the core. Numerical tests of the influence of this characteristic of the basin modeling approach on the fluid flow could be found in Moretti (1998). The benchmarks presented in this paper showed that the key point to understand a migration pathway is the connection between the carried bed and the leakage path, which could be the damage zone of the faults, rather than the intrinsic permeability of the material. References Armijo, R., Meyer, B., King, G.C., Rigo, A., Papanastassiou, D., 1996. Quaternary evolution of the Corinth rift and its implications for the late Cenozoic evolution of the Aegean. Geophysical Journal International 126, 11–53. Barton, C.C., La Pointe, P.R., 1995. Fractals in Earth Sciences. Plenum Press, New York. Barton, C.C., Larsen, E., 1985. Fractal geometry of two-dimensional fracture network at Yucca Mountains, SW Nevada. In: Stephennson, O. (Ed.), Fundamentals of Rock Joints Proceedings in the International Symposium of Fundaments of Rock Joints, Bjorkkliding, Sweden, pp. 77–84. Bernard, P., Briole, P., Meyer, B., Lyon-Caen, H., Gomez, G.M., Tiberi, C., Berge, C., Cattin, R., Hatzfeld, D., Lachet, C., Deschamps, A., Courboulex, F., Larroque, C., Rigo, A., Massonet, D., Papadimitriou, P., Kassaras, J., Diagourtas, D., Macropoulos, K., Veis, G., Papazisi, E., Mitsakaki, C., Karakostas, V., Papadimitriou, E., Papanastassiou, D., Chouliaras, G., Stravakakis, G., 1997. The Ms =6.2, June 15, 1995 Aigion earthquake (Greece): evidence for low angle normal faulting in the Corinth rift. Journal of Seismology 1, 131–150. Billi, A., Salvini, F., Storti, F., 2003. The damage zones–fault core transition in carbonate rocks: implication for fault growth, structure and permeability. Journal of Structural Geology 25, 1779–1794. Billiris, H., Paradissis, D., Veis, G., England, P., Featherstone, W., Parson, B., Cross, P., Rands, P., Rayson, M., Sellers, P., Ashkenazi, V., Daavison, M., Jackson, J., Ambraseys, N., 1991. Geodetic determination of tectonic deformation in central Greece from 1900 to 1988. Nature 350, 124–129.

L. Micarelli et al. / Tectonophysics 426 (2006) 31–59 Briole, P., Rigo, A., Lyon-Caen, H., Ruegg, J., Papazissi, K., Mistakaki, C., Balodimou, A., Veis, G., Hatzefeld, D., Deschamps, A., 2000. Active deformation of the Gulf of Korinthos, Greece: results from repeated GPS surveys between 1990 and 1995. Journal of Geophysical Research 105 (11), 25605–25625. Brooks, M., Ferentinos, G., 1984. Tectonics and sedimentation in the gulf of Corinth and the Zakynos and Kefallinia channels, western Greece. Tectonophysics 101, 25–54. Caine, J.S., Evans, J.P., Forster, C.B., 1996. Fault zone architecture and permeability structure. Geology 11, 1025–1028. Carter, K.E., Winter, C.L., 1995. Fractal nature and scaling of normal faults in the Espanola Basin, Rio Grande Rift, New Mexico: implications for fault growth and brittle strain. Journal of Structural Geology 17, 863–873. Cello, G., 1997. Fractal analysis of a Quaternary fault array in the central Apennines, Italy. Journal of Structural Geology 19 (7), 945–953. Cello, G., Gambini, R., Mazzoli, S., Read, A., Tondi, E., Zucconi, V., 2000. Fault zone characteristics and scaling properties of the Val d'Agri fault system (southern Apennines, Italy). Journal of Geodynamics 29, 293–307. Cello, G., Tondi, E., Micarelli, L., Invernizzi, C., 2001. Fault zone fabrics and geofluid properties as indicators of rock deformation modes. Journal of Geodynamics 32, 543–565. Chester, F.M., Logan, J.M., 1986. Implications for mechanical properties of brittle faults from observations of the Punchbowl Fault zone, California. Internal structure of fault zones. Pure and Applied Geophysics 124, 77–106. Chester, F.M., Evans, J.P., Biegel, R.L., 1993. Internal structure and weakening mechanisms of the San Andreas fault. Journal of Geophysical Research 98, 771–786. Childs, C., Walsh, J.J., Watterson, J., 1990. A method for estimation of density of fault displacement below the limit of seismic resolution in reservoir formations. In: Buller, A.T., et al. (Eds.) North Sea Oil and Reservoirs, vol. II. Norwegian Institute of Technology, pp. 309–318. Clarke, P.J., Davies, R.R., England, P.C., Parson, B.E., Billiris, H., Paradissis, V., Veis, G., Denys, P.H., Cross, P.A., Ashkenazi, V., Bingley, R., 1997. Geodetic estimate of seismic hazard in the Gulf of Korinthos. Geophysical Research Letters 24, 1303–1306. Clément, C., 2000. Imagerie sismique crustale de la subduction hellénnique et du golfe de Corinthe. Ph.D. Thesis, University Paris VII, pp.175. Collier, R., Dart, C., 1991. Neogene to Quaternary rifting, sedimentation and uplift in the Corinth Basin, Greece. Journal of the Geological Society of London 148, 1049–1065. Collier, R., Gawthorpe, R.G., 1995. Neotectonics, drainage and sedimentation in central Greece: insights into coastal reservoir geometries in syn-rift sequences. Hydrocarbon Habitat in Rift BasinsGeological Society of London Special Publication, vol. 80, pp. 165–181. Collier, R., Leeder, M.R., Rowe, P.J., Atkison, T.C., 1992. Rates of uplift in the Corinth and Megara Basins, central Greece. Tectonics 11, 1159–1167. Cornet, F.H., Doan, M.L., Moretti, I., Borm, G., 2004a. Drilling through the active Aigion Fault: the AIG10 well observatory. C.R. Geoscience 336, 395–406. Cornet, F.H., Bernard, P., Moretti, I., 2004b. The Corinth Rift Laboratory. C.R. Geoscience 336, 235–241. Cowie, P.A., Knipe, R.J., Main, I.J., 1996. Scaling laws for fault and fracture populations: analyses and applications. Journal of Structural Geology 18 (2/3), 135–383 (Special Issue).

57

Curewitz, D., Karson, J.A., 1997. Structural setting of hydrothermal outflow: fracture permeability maintained by fault propagation and interaction. Journal of Volcanology and Geothermal Research 79, 149–168. Daniel, J.M., Moretti, I., Micarelli, L., Eyssautier-Chuine, S., Delle Piane, C., 2004. Faulting in prefractured carbonate: macroscopic structural analysis of Ag10 Well (Gulf of Corinth, Greece). C.R. Geoscience 336, 435–444. Dart, C., Collier, R., Gawthorpe, R., Keller, J.V.A., Nichols, G., 1994. Sequence stratigraphy of (?)Pliocene–Quaternary synrift, Gilberttype fan deltas, northern Peloponnese, Greece. Marine and Petroleum Geology 11, 545–560. Davies, R.R., England, P.C., Parson, B.E., Billiris, H., Paradissis, D., Veis, G., 1997. Geodetic strain of Greece in the interval 1892– 1992. Journal of Geophysical Research 102, 24571–24588. De Martini, P., Pantosti, D., Palyvos, N., Lemeille, F., McNeill, L., Collier, R., 2004. Slip rates of the Aigion and Eliki Faults from uplifted marine terraces, Corinth Gulf, Greece. C.R. Geoscience 336, 325–334. Doligez, B., Ungerer, P., Chenet, P., Burrus, J., Bessis, F., Bessereau, G., 1987. Numerical modeling of sedimentation, heat transfer, hydrocarbon formation and fluid migration in the Viking1223 graben, North Sea. In: England, W.A., Flett, A.J. (Eds.), Petroleum Geology of Northwest Europe. Heyden, London, pp. 1039–1048. Doutsos, T., Poulimenos, G., 1992. Geometry and kinematics of active faults and their seismotectonic significance in the western Corinth–Patras rift (Greece). Journal of Structural Geology 14 (6), 689–699. Du Bernard, X., Labaume, P., Darcel, C., Davy, P., Bour, O., 2002. Cataclastic slip band distribution in normal fault damage zones, Nubian sandstones, Suez rift. Journal of Geophysical Research 107 (B7), 10.1029. Fossen, H., Rornes, A., 1996. Properties of fault populations in the Gullaks Field, northern North Sea. Journal of Structural Geology 18, 179–190. Frima, C., Moretti, I., Brosse, E., Quattrocchi, F., Pizzino, L., 2005. Can diagenetic processes influence the short term hydraulic behaviour evolution of a fault? Oil and Gas Technology 60 (2), 213–230. Gauthier, B.D., Lake, S.D., 1993. Probabilistic modelling of fault below the limit of seismic resolution in Pelican Field, North Sea, Offshore U.K. Bulletin of the American Association of Petroleum Geologists 77, 761–777. Gawthorpe, R.G., Fraser, A.J., Collier, R., 1994. Sequence stratigraphy in active extensional basins: implications for the interpretation of ancient basin fills. Marine and Petroleum Geology 11, 642–658. Ghisetti, F., Vezzani, L., 2004. Plio-Pleistocene sedimentation and fault segmentation in the Gulf of Corinth (Greece) controlled by inherited structural fabric. C.R. Geoscience 336, 243–250. Ghisetti, F.C., Vezzani, L., Agosta, F., Sibson, R., Moretti, I., 2001. Tectonic setting and sedimentary evolution of the south-west margin of the Corinth rift (Aigion–Xilocastro area). IFP Report, vol. 562 07. Giurgea, V., Rettenmaier, D., Pizzino, L., Unkel, I., Hötzl, H., Förster, A., Quattrocchi, F., 2004. Preliminary hydrogeological interpretation of the Aigion area from the AIG-10 borehole data. C.R. Geoscience 336, 467–475. Hammond, K.J., Evans, J.P., 2003. Geochemistry, mineralization, structure, and permeability of a normal-fault zone, Casino mine, Alligator Ridge district, north central Nevada. Journal of Structural Geology 25 (5), 717–736.

58

L. Micarelli et al. / Tectonophysics 426 (2006) 31–59

Hatzfeld, D., Karakostas, V., Ziazia, M., Kassaras, I., Papadimitriou, E., Makropoulos, K., Voulgaris, N., Papaioannou, 2000. Microseismicity and faulting geometry in the Gulf of Corinth (Greece). Geophysical Journal International 141, 438–456. Heffer, K.J., Bevan, T.G., 1990. Scaling relationships in natural fractures — data, theory and applications. Proceedings of European Petrology Conference 2, 367–376. Hesthammer, J., Johansen, T.E.S., Watts, L., 2000. Spatial relationships within fault damage zones in sandstones. Marine and Petroleum Geology 17, 873–893. Hirata, T., 1989. Fractal dimension of fault systems in Japan: fractal structure in rock fracture geometry at various scales. Pure and Applied Geophysics 131, 157–169. Jackson, S., McKenzie, D., 1988. Rates of active deformation in the Aegean Sea and surrounding regions. Basin Research 1, 121–128. Jackson, S., Sanderson, D.J., 1992. Scaling of fault displacement from the Badajoz–Cordoba shear zone, SW Spain. Tectophysics 210, 179–190. Jolivet, L., Brun, J.P., Gautier, P., Lallemant, S., Patriat, M., 1994. 3D kinematics of extension in the Aegean region from the early Miocene to the present, insights from the ductile crust. Bullettin de la Société Géologique de France 165 (3), 195–209. Keraudren, F., Sorel, D., 1987. The terraces of Corinth (Greece) a detailed record of eustatic sea level variations during the last 500000 years. Marine Geology 77 (1–2), 99–107. Knott, S.D., Beach, A., Brockbank, P.J., Brown, J.L., Mc Callum, J.E., Welbon, A.I., 1996. Spatial and mechanical controls on normal fault populations. Journal of Structural Geology 18, 359–372. Koukouvelas, I.K., Doutsos, T., 1996. Implication of structural segmentation during earthquakes: the 1995 Egion earthquake, Gulf of Corinth, Greece. Journal of Structural Geology 18 (12), 1381–1388. Labaume, P., Carrio, E., Gamond, J.F., Renard, F., 2004. Deformation mechanisms and fluid flow-driven mass transfers in the recent fault zone of the Corinth rift (Greece). C.R. Geoscience 336, 375–384. Latorre, D., Virieux, J., Monfret, T., Monteiller, V., Vanorio, T., Got, J.-L., Lyon-Caen, H., 2004. A new seismic tomography of Aigion area (Gulf of Corinth, Greece) from the 1991 data set. Geophysical Journal International 159, 1013–1031. Laubach, S.E., 1992. Fracture networks in selected Cretaceous sandstones of the Green River and San Juan basins, Wyoming, New Mexico and Colorado. In: Schmoker, J.W., Coalson, E.B., Brown, C.A. (Eds.), Geological Studies Relevant to Horizontal Drilling: Examples from Western North America. Rocky Mountain Association of Geologists, pp. 115–127. Le Pourhiet, L., Burov, E., Moretti, I., 2004. Rifting through a stack of inhomogeneous thrusts (study case in the Gulf of Corinth). Tectonics 23 (4), TC4005. Linn, A., Shimamoto, T., Maruyama, T., Sigetomi, M., Miyata, T., Takemura, K., Tanaka, H., Uda, S., Murata, A., 2001. Comparative study of cataclastic rocks from a drill core and outcrops of the Nojima Fault zone on Awaji Island, Japan. The Island Arc 10, 368–380. Lyon-Caen, H., Papadimitropoulos, P., Deschamps, A., Bernard, P., Makropoulos, K., Pacchiani, F., Patau, G., 2004. First results of the CRLN seismic network in the western Corinth rift: evidence of old fault reactivation. C.R. Geoscience 336, 343–352. Malartre, F., Ford, M., Williams, E.A., 2004. Preliminary biostratigraphy and 3D lithostratigraphy of the Vouraikos Gilbert-type fan delta. C.R. Geoscience 336, 269–280. Mandelbrot, B.B., 1983. The Fractal Geometry of Nature. Freeman Press, New York.

Marrett, R.A., Allmendinger, R.W., 1992. Amount of extension on “small” faults: an example from the Viking graben. Geology 20, 47–50. Mattioni, L., Moretti, I., Le Pourhiet, L., 2004. Extension through a heterogeneous crust. The case of Gulf of Corinth (Greece). Part I: analogue modelling. Bollettino di Geofisica 45, 237–241. McKenzie, D., 1978. Active tectonics of the Alpine–Himalayan belt: the Aegean Sea and surrounding regions. Geophysical Journal of the Royal Astronomical Journal 55, 217–254. Micarelli, L., Daniel, J.M., Moretti, I., 2002a. Structural characterization of Quaternary fault zones in the Aigion area (Greece). EGS XXVII General AssemblyGeophysical Research Abstracts, Nice, 21–26 April, 2002, France, vol. 4. Micarelli, L., Daniel, J.M., Moretti, I., 2002b. Scaling properties and structural characterization of Quaternary fault zones in the southwestern Gulf of Corinth (Greece). International Workshop “Active Faults: Analysis, Processes and Monitoring”, Abstract Volume, Camerino, 3–6 June, 2002, Italy. Micarelli, L., Moretti, I., Daniel, J.M., 2003. Structural properties of rift-related normal faults: the case study of the Gulf of Corinth, Greece. Journal of Geodynamics 36, 275–303. Micarelli, L., Daniel, J.M., Moretti, I., 2004. Structural characteristic of Quaternary fault zones in the south-western Gulf of Corinth (Greece). Studi Geologici Camerti, Special Volume/2004. Micarelli, L., Benedicto, A., Invernizzi, C., Saint-Bezar, B., Michelot, J.L, Vergely, P., 2005. Influence of P/T conditions on the style of normal fault initiation and growth in limestones from the SEBasin, France. Journal of Structural Geology 27, 1577–1598. Moretti, I., 1998. The role of fault in hydrocarbon migration. Petroleum Geoscience 4, 81–94. Moretti, I., Naville, C., 2001. Seismic survey and interpretation, well implantation. IFP Report, vol. 56241. 44 pp. Moretti, I., Delhomme, J.P., Cornet, F., Bernard, P., SchmidtHattenberger, C., Born, G., 2002. The Corinth Rift Laboratory: monitoring of active faults. First Break 20.2, 91–97. Moretti, I., Sakeleriou, D., Lykousis, V., Micarelli, L., 2003a. The Gulf of Corinth: an active half graben? Journal of Geodynamics 36, 323–340. Moretti, I., Micarelli, L., Daniel, J.M., Eyssautier, S., Frima, C., 2003b. The cores of AG-10. Tech. Rep., IFP, vol. 57240. Moretti, I., Lykousis, V., Sakellariou, D., Reynaud, J.Y., Benziane, B., Prinzhoffer, A., 2004. Subsidence rate in the Gulf of Corinth : what we learn from the long piston coring. C.R. Geoscience 336, 291–299. Moulouel, H. 2004. Etude de la fracturation des carbonates à proximité d'une faille normale active à partir des carottes et de diagraphies du puits AIG-10; conséquences sur les propriétés de transfert des zones de faille. Master thesis Paris VI and IFP (in French). IFP Rapport 58324, pp. 69. Myriantis, M.L., 1984. Graben formation and associated seismicity in the Gulf of Korinth (central Greece). In: Dixon, J.E., Robertson, A.H.F. (Eds.), The Geological Evolution of the Eastern MediterraneanGeoloGeological Society Special Publication, vol. 17, pp. 701–707. Naville, C., Serbutoviez, S., Moretti, I., Daniel, J.M., Throo, A., Girard, F., Sotiriou, A., Tselentis, A., Skarpzelos, Ch., Brunet, Ch., Cornet, F., 2004. Pre-drill surface seismic in vicinity of AIG-10 well and post-drill VSP. C.R. Geoscience 336, 407–414. Needham, T., Yielding, C., Fox, R., 1996. Fault population description and prediction using examples from the offshore U.K. Journal of Structural Geology 18, 155–167. Ori, G.G., 1989. Geologic history of the extensional basin of the Gulf of Corinth (?Miocene–Pleistocene), Greece. Geology 17, 918–921.

L. Micarelli et al. / Tectonophysics 426 (2006) 31–59 Ortega, O., Marrett, R., 2000. Prediction of macrofracture properties using microfracture information, Mesaverde Group sandstones, San Juan basin, New Mexico. Journal of Structural Geology 22 (5), 571–588. Peacock, D.C.P., Sanderson, D.J., 1994. Strain and scaling of faults in the chalk at Flamborough Head, U.K. Journal of Structural Geology 16, 97–107. Perissotaris, C., Piper, D.J., Lykoussis, V., 2000. Alternating marine and lacustrine sedimentation during the late Quaternary in the Gulf of Corinth rift basin, central Greece. Marine Geology 167, 391–411. Pickering, G., Bull, J.M., Sanderson, D.J., 1995. Sampling power-law distribution. Tectonophysics 148 (1), 20. Pitilakis, K., Makropoulos, K., Bernard, P., Lemeille, F., Lyon-Caen, H., Berge-Thierry, C., Tika, T., Manakou, M., Diagourtas, D., Raptakis, D., Kallioglou, P., Makra, K., Pitilakis, D., Bonilla, F., 2004. The Corinth Gulf Soft Soil Array (CORSSA) to study site effects. C.R. Geoscience 336, 353–365. Pizzino, L., Quattrocchi, F., Cinti, D., Galli, G., 2004. Fluid geochemistry along the Eliki and Aigion seismogenic segments (Gulf of Corinth, Greece). C.R. Geoscience 336, 367–374. Poulimenos, G., 1993. Tectonics and sedimentation in the western Corinth Graben, Greece. Neues Jahrbuch fur Geologie und Palaonntologie Monatshefte 10, 607–630. Poulimenos, G., 2000. Scaling properties of normal fault populations in the western Corinth Graben, Greece: implication for fault growth in large strain setting. Journal of Structural Geology 22, 307–322. Poulimenos, G., Gisbert, A., Doutsos, T., 1989. Neotectonic evolution of the central section of the Corinth Graben. Zeitschrift der deutschen geologischen Gesellschaft 140, 173–182. Rigo, A., Lyon-Caen, H., Armijo, R., Deschamps, A., Hatzfeld, D., Makioupoulos, K., Papadimitriou, P., Kassaras, I., 1996. A microseismic study of the western part of the Gulf of Corinth (Greece): implication for the large-scale normal faulting mechanisms. Geophysical Journal International 126, 663–688. Roberts, G.P., 1996. Variation in fault-slip directions along active and segmented Norman fault systems. Journal of Structural Geology 18, 835–845. Roberts, S., Jackson, J., 1991. Active normal faulting in central Greece: an overview. In: Roberts, A.M., Yielding, G., Freeman, B. (Eds.), The Geometry of Normal FaultsGeological Society of London, Special Publication, vol. 56, pp. 125–142. Schmidt, J., 1879. Studien uber Erdbeben. Carl Schottze, Leipzig, pp. 68–83.

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Schneider, F., Wolf, S., Faille, I., Pot, D., 2000. A 3D basin model for hydrocarbon potential evaluation: application to Congo offshore. Oil and Gas Science and Technology Rev. IFP 55 (1), 3–13. Shipton, Z.K., Cowie, P.A., 2001. Damage zone and slip-surface evolution over μm to km scales in high-porosity Navajo sandstone, Utah. Journal of Structural Geology 23, 1825–1844. Sibson, R.H., 1977. Fault rocks and fault mechanisms. Journal of the Geological Society of London 133, 191–231. Sibson, R.H., 1994. Crustal stress, faulting and fluid flow. In: Parnell, J. (Ed.), Geofluids: Origin, Migration and Evolution of Fluids in Sedimentary BasinGeological Society of London, Special Publication, vol. 78, pp. 69–84. Stewart, I., 1996. Holocene uplift and palaeoseismicity on the Eliki Fault, western Gulf of Corinth, Greece. Annali di Geofisica 39, 575–588. Stewart, I., Vita-Finzi, C., 1996. Coastal uplift on active normal faults: the Eliki Fault, Greece. Geophysical Research Letters 23, 1853–1856. Tselentis, G.A., Makropoulos, K., 1986. Rates of crustal deformation in the Gulf of Corinth (central Greece) as determined from seismicity. Tectonophysics 24, 55–61. Ungerer, P., 1990. State of art of research in kinetic modeling of oil formation and expulsion. Organic Geochemistry 16, 1–25. Vermilye, J.M., Scholz, C.H., 1998. The process zone: a microstructural view of fault growth. Journal of Geophysical Research 103 (B6), 12223–12237. Walsh, J.J., Watterson, J., 1992. Populations of fault displacements and their effects on estimates of fault-related regional extension. Journal of Structural Geology 14, 701–712. Walsh, J.J., Watterson, J., 1993. Fractal analysis of fracture patterns using the standard box-counting technique: valid and invalid methodologies. Journal of Structural Geology 15, 1509–1512. Walsh, J.J., Watterson, J., Yielding, G., 1994. Determination and interpretation of fault size populations: procedures and problems. In: Buller, A.T., et al. (Ed.), North Sea Oil and Gas Reservoirs, vol. III. Norwegian Institute of Technology, pp. 141–155. Wilson, J.E., Chester, J.S., Chester, F.M., 2003. Microfracture analysis of fault growth and wear processes, Punchbowl Fault, San Andreas system, California. Journal of Structural Geology 26 (11), 1855–1873. Wojtal, S.F., 1996. Changes in fault displacement populations correlated to linkage between faults. Journal of Structural Geology 18, 265–279.