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Structural–dynamic model of the Chersky seismotectonic zone (continental part of the Arctic–Asian seismic belt)
Accepted Manuscript Structural–Dynamic Model of The Chersky Seismotectonic Zone (Continental Part of The Arctic–Asian Seismic Belt) L.P. Imaeva, V.S. Imaev, B.M. Koz’min PII: DOI: Reference:
S1367-9120(15)30139-5 http://dx.doi.org/10.1016/j.jseaes.2015.11.010 JAES 2563
To appear in:
Journal of Asian Earth Sciences
Received Date: Revised Date: Accepted Date:
21 April 2015 15 October 2015 13 November 2015
Please cite this article as: Imaeva, L.P., Imaev, V.S., Koz’min, B.M., Structural–Dynamic Model of The Chersky Seismotectonic Zone (Continental Part of The Arctic–Asian Seismic Belt), Journal of Asian Earth Sciences (2015), doi: http://dx.doi.org/10.1016/j.jseaes.2015.11.010
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STRUCTURAL–DYNAMIC MODEL OF THE CHERSKY SEISMOTECTONIC ZONE (CONTINENTAL PART OF THE ARCTIC–ASIAN SEISMIC BELT) L.P. Imaeva1, V.S. Imaev1, 3, B.M. Koz’min2
1
Institute of the Earth’s Crust, Siberian Division, Russian Academy of Sciences, 128
Lermontova St., Irkutsk 664033, Russia 2
Diamond and Precious Metal Geology Institute, Siberian Division, Russian Academy of
Sciences, 39 Lenin Prospekt, Yakutsk, Sakha Republic (Yakutia), 677891, Russia 3
Technical Institute (Branch) of the North Eastern Federal University, 16 Kravchenko,
Neryungri 678960, Russia
Abstract To construct a model for modern geodynamics of the Chersky seismotectonic zone (continental part of the Arctic-Asian seismic belt) we analyzed the available data on its structural-tectonic setting, depth structure, kinematics of active faults, morphotectonic features of modern topography, tectonic stress fields as derived from the earthquake focal mechanisms as well as the types of Late Cenozoic fold and rupture deformation. It is established that the YanaIndigirka and Indigirka-Kolyma segments in the central part of the Chersky zone underwent transpression due to collision of the Eurasian (EU) and North American (NA) lithospheric plates. This was only possible if, in course of the plate convergence, the Kolyma-Omolon block in the frontal part of the NA plate formed the active indentor. Under the block pressure, geodynamic settings experience horizontal compression, in which case some of the blocks are being extruded along the system of northwestern and southeastern strike-slip faults. This results in the formation of major seismogenic structures with a high seismic potential in the marginal and frontal parts of the Chersky zone.
Keywords: Arctic-Asian seismic belt, Chersky seismotectonic zone, Kolyma-Omolon block, active fault, earthquake focal mechanism, type of Late Cenozoic deformations, indentor, structural-dynamic model.
1 Introduction Combined geological-geophysical and seismological studies in northeast Asia revealed the extensive Arctic-Asian seismic belt (AASB) (Fig. 1), which marks the boundary between the major North American and Eurasian lithospheric plates (Chapmen and Solomon 1976, Imaev et al. 2000, Fujita et al. 2009). Geodynamic processes occurring within the belt cause seismotectonic deformation of the Earth’s crust in the zone of contact between the plates. Tectonically, the AASB can be divided into major regional segments (Laptev Sea, Kharaulakh, Chersky, and Sea of Okhotsk) (Imaev et al. 1990). Structural paragenesis of active faults developed in the segments is controlled by the stress state of the Earth’s crust (Imaev et al. 2000, 2009, Koz’min et al. 2001). Instrumental seismic observations conducted by Geophysical Surveys of Russian Academy of Sciences and its Siberian Branch (http://www.ceme.gsras.ru) and the Michigan State University (USA) (Mackey et al. 2007) in northeast Russia, and available geological-structural (Parfenov et al. 2001) and morphotectonic (Imaeva et al. 2009) data helped elucidate the dynamics of seismogenic structures of constituent segments of the Chersky seismotectonic zone (CSZ) and develop a regional structural-dynamic model. The investigations were aimed at: -
analyzing
the
published
structural-tectonic,
geological-geophysical
and
seismological data and compiling additional morphotectonic maps for the region; -
estimating effect of reactivated Late Mesozoic structures on Cenozoic tectonics and modern structural pattern;
-
making structural-dynamic analysis of the strong earthquakes epicentral zones and refining the kinematics of active faults;
-
elucidating the kinematics of motions and developing regional structural-dynamic models of major seismogenic structures in some CSZ segments.
Below two local segments within Mesozoides of the CSZ, which are the Yana-Indigirka and Indigirka-Kolyma (Okhotsk) segments, are considered. Their location is shown in Fig.1. The segments were recognized by specific structural paragenesis of active faults characteristic of certain types of crustal stress state (Gusev 1979, Imaeva et al. 2011, Parfenov et al. 2001), geophysical field structures (Suvorov and Kornilova 1986, Imaev et al. 2000), morphotectonic features (Imaev et al. 2000, 2009) and dynamics of major seismogenic structures (Imaev et al. 2009, Imaeva et al. 2009) of the segments.
2 The Yana-Indigirka segment The segment is represented, morphotectonically, by deformation structures developed on the northern and northwestern flanks of the frontal zone of interaction between the EU and NA plates (Fig. 2). Their zone of collision has specific deep structure (Suvorov and Kornilova 1986, Imaev et al. 2000), representing a collage of terranes that originated under different geodynamic conditions (Parfenov et al. 2001) and are characterized by a specific morphotectonic complex of faults and blocks (Imaev et al. 2000, 2009). Tectonically, the segment includes frontal zones of the Kolyma-Omolon block and a number of terranes (Polousny-Debin, Omulevka, Nagodzha, etc.) of different geodynamic nature located to the north and northwest of the sharp eastward bend of the Indigirka River (Fig. 2). The terranes are broken by a series of northwestern faults mostly of left-lateral strike-slip kinematics into some blocks (Imaev et al. 2000, Imaeva et al. 2011), of which the largest are TasKhayakhtakh and Selennyakh (Fig. 2). Late Mesozoic faults, which were reactivated in the Cenozoic, played a decisive role in shaping the modern topography of the Yana-Indigirka segment. Analysis of the kinematics of active faults and deformation of Cenozoic deposits in the northeastern flank of the Yana-
Indigirka segment (Imaev et al. 2000, 2009, Imaeva et al. 2009, 2010) showed they are mostly thrust, reverse and strike slip faults. The amount of horizontal displacement along these faults is estimated at a few tens of kilometers (Gusev 1979). Most representative for analyzing the dynamics of the formation of seismogenic structures in the segment is the fault system traceable along the axial part of the Moma Ridge within the Ilin-Tas folded zone (Fig. 3). In plan view, the southern sides of the Ilin-Tas leftlateral and the Arga-Tas right-lateral strike slip faults (Fig.4, Nos.10 and 11) join at an obtuse angle at about the center of the Moma Ridge. To the northwest and southeast of their contact zone there are fan-like zones of compression represented by folds in Cenozoic rocks of the Indigirka-Zyryanka basin and the Moma-Selennyakh depressions (Imaev et al. 2000, 2009, Imaeva et al. 2009, 2011). In front of the junction of the faults a zone of extension occurs, which is morphologically expressed as a sublatitudinal valley of the mid-Moma River. This is evidenced indirectly by the presence there of the Balagan-Tas volcano of Cenozoic age, the world’s largest Moma icing and numerous mineralized thermal groundwater springs (Grachev 1996). The stress state of the Earth’s crust was determined from the focal mechanisms of earthquakes detected in the zone of interaction of the Kolyma-Omolon block and the Eurasian plate (Table 1). Analysis of active tectonic elements and seismic manifestations revealed that motions in the foci of strong earthquakes coincide with the kinematics of the active faults they are confined to. Characteristic of the earthquakes within the CSZ is that they all occur under conditions of stable NE-SW compression. The compressive stresses (σ 3) are subhorizontal (dip angles 3 to 44º), and they act across the strike of structural elements of the territory. Tensile stresses (σ1) often act along the fault lines and are oriented both horizontally and subvertically with respect to the Earth’s surface (dip angles 2 to 85°). The intermediate stress axes (σ 2) show random orientation in space and are inclined to the horizon at the angles of 0 to 82º. This stress
pattern is seen in the earthquake foci all the way from North Verkhoyansk to the Sea of Okhotsk (Figs. 3, 4). Orientation of major tectonic stresses as derived from seismological data confirms that motions in the earthquake foci within the CSZ are mostly reverse, thrust and strike slip faults. Out of 30 determinations, 39% are reverse faults, 30% strike slips, 17% thrusts and the rest (14%) is combination of strike slips and normal faults (Imaev et al. 2000, Koz’min et al. 2001). The data obtained indicate that seismic processes within the CSZ proceed under dominant compression with active development of reverse faults, strike slips and their combinations (Fig. 4). This is well evidenced by the structural patterns of major seismogenic areas over the entire CSZ. Specifically, the band of epicenters observed along the Ulakhan fault line (Fig. 4, N16) continues onto the left bank of the Indigirka River, and then at about 140º-141ºE it changes sharply its northwestern orientation to longitudinal one (Fig. 1). The band cuts across the strike of the Moma-Selennyakh basin system, and along the western slope of the Andrei-Tas Ridge where it can be traced up to the Polousny Range (Fig. 3) in the zone of influence of the Selennyakh fault (Fig. 4, No.8). In the Yana-Indigirka segment, several seismic activity maxima are recognized (Fig.3). The highest maximum occurs within the Andrei-Tas block where along with numerous weak shakes the 1984 Uyandina earthquake (intensity VII, M s =5.6), the 1999 event (intensity VI-VII, Ms =5.2); the 2008 Andrei-Tas event (intensity VIII, Ms =6.1) and the 2013 Ilin-Tas quake (intensity IX, Ms =6.9) have been reported (Figs. 2, 3). Isoseism maps were compiled for many of the strong earthquakes within the CSZ (Koz’min 1984, Imaev et al. 2000, Imaeva et al. 2011). The tendency observed here is that all isoseisms outlining areas of certain earthquake intensity have a form of an ellipse with its great axis elongated in a northwestern direction along the lines of major seismically active faults (Table 2). The exception is provided by isoseisms of earthquakes in the seismic maximum within the Andrei-Tas block (Imaeva et al. 2009, 2011).
It is established that isoseisms of earthquakes within the Andrei-Tas block crosscut active faults, in contrast to areas NW and SE of the block where isoseisms are elongated parallel to the faults. This may be explained by maximum pressure exerted by the Kolyma-Omolon block on the EU plate on the northeast (Figs. 1, 3). It is likely that here, in the zone of the EU and NA contact, compression causes accumulation of significant tectonic stresses resulting in activation of seismotectonic processes. The general sense of the movement of the Kolyma-Omolon block is determined from the spatial position of isoseisms which are, under the block effect, oriented NESW across the structural elements. This dynamic setting favored the formation, to the north and northwest of the area of maximum pressure of the block, of transverse zones of compression represented by a system of reverse faults and thrusts (Polousny region) and multiple folding episodes of folds on folds in Cenozoic deposits of the Indigirka-Zyryanka basin. Thus, under conditions of transpression, a specific dynamic setting has developed within the Yana-Indigirka segment as a result of interaction of frontal structures of the EU and NA plates at their boundary. Such dynamic setting is possible if the Kolyma-Omolon block joins the leading edge of the NA plate to become an active indentor during the plates convergence. This resulted in the formation, in front of the indentor, of diverging NW-striking sinistral and SEstriking dextral strike slips which developed, at their ends, systems of seismogenic reverse faults and thrusts with a maximum seismic potential.
3 The Indigirka-Kolyma (Okhotsk) segment-block The Indigirka-Kolyma block is a northern fragment of the Sea of Okhotsk crustal plate also known as a terrane under the same name (see Fig. 1). It occurs to the east of the southern sector of the Verkhoyansk fold-and-thrust belt from which it is separated by the right-striking KetandaUl’beya zone (Fig. 1 and Fig. 4, Nos.19 and 20). The basement of the Okhotsk terrane is made of Archean and Early Proterozoic crystalline schists and gneisses of the granulite and amphibolite
metamorphic facies (Gusev 1979, Leonov et al. 2009). Most of the terrane is covered by flatlying volcanites of the Okhotsk-Chukotka belt. Spatial distribution of seismicity permitted the recognition of three zones of high seismotectonic activity in the segment, where seismicity is clustered in extensive diffuse bands confined to the zones of influence of the faults bounding the Indigirka-Kolyma (Okhotsk) block on the west, northeast and south. In the first band (Fig. 1), the earthquake epicenters are concentrated along the sublongitudinal Ketanda-Ul’beya strike-slip fault system (Fig.4, Nos.19 and 20). Focal mechanisms of the events that occurred here in 1977, 1984 and 1986 point to the east-northeast orientation of compressive stresses and dextral strike-slip motions in their foci. The second seismic band is confined to the most active Ulakhan and Chai-Yureya faults (Fig 4, Nos.16 and 14) along which the largest seismic events were registered in the period from 1974 to 1992. Focal mechanism solutions indicate left-lateral strike-slip motions in the earthquake foci where compressive stresses are NE-SW oriented (Imaev et al. 2000, Koz’min et al. 2001). The third band (Fig. 1) is restricted to the zone of influence of the sublatitudinal Chelomdzha-Yama left-lateral strike slip with a reverse fault component (Fig. 4, No. 21). It extends along the northern coast of the Sea of Okhotsk. The focal mechanism of the 2001 earthquake with the epicenter located within this fault also corresponds to left-lateral motions in its focus. All of the above mentioned fault systems are well-defined in geophysical field maps. Most mobile is the northeast boundary of the Indigirka-Kolyma (Okhotsk) block (second band), which represents a zone of contact between the North American and the Sea of Okhotsk plates, and is confined to the southeast flank of the CSZ. A high earthquake density is also registered at the southern boundary of the block (third band) where the epicenters are traced along the northern shore of the Sea of Okhotsk to the western coast of Kamchatka and in the northern part of the Sea of Okhotsk floor. This band coincides with the thrust of the ancient
Benioff seismic zone (Nokleberg et al., 2000). The Ketanda-Ul’beya zone (first band) at the western boundary of the block is marked by a somewhat lower seismic activity. All events detected within the block are crustal in depth (up to 30 km) (Imaev et al. 2000, Koz’min et al. 2001). Focal mechanism parameters of strong earthquakes and kinematics of active faults developed within the discussed Indigirka-Kolyma block showed the prevalence of horizontal motions (Table 1). Vertical motions (reverse faults, thrusts, and normal faults) are subordinate. Most representative is the en-echelon system of strike-slip faults at the northeastern boundary of the block of which the most active is the Ulakhan fault. It forms a dynamic pair with the Darpir fault. Both faults are clearly visible on mid- and large-scale satellite images and aerial photographs, and are expressed as continuous straight lineaments of northwest strike on topographic maps. The Ulakhan fault and the Darpir fault (Fig. 4, Nos.16 and 15) meet at an angle of 20-25 o and bound the Omulevka block of Paleozoic rocks (elevated 450-550 m asl) surrounded by Mesozoic deposits (Fig. 4). The Omulevka block was squeezed out to the surface as a result of horizontal deformations (Fig. 7). The Ulakhan-Darpir dynamic pair most clearly demonstrates the type of deformation processes at the boundary of the North American and Sea of Okhotsk plates. According to present tectonic models, the Omulevka block is a separate terrane incorporated in the Mesozoic structural framework in the processes of collisional and postcollisional transformations of the structure of the Verkhoyansk-Kolyma Mesozoides (Parfenov et al., 2001). The activity of the Ulakhan fault and the Darpir fault is nowadays confirmed not only by numerous earthquake epicenters but also by a series of paleoseismic dislocations and presentday deformations of the Earth’s crust (landslides, rock-slides, rockfalls ets) found in the zones of influence of the faults (Imaev et al., 2000). The facts that the Omulevka block is bounded by the Ulakhan and Darpir strike-slip faults of opposing kinematics (Fig. 7), that its frontal part is
deformed by reverse faults and thrusts, and that a number of shallow small seismic events were recorded there all indicate that the block was formed by the detachment mechanism. The territory to the south of the Indigirka-Kolyma (Okhotsk) segment-block is represented, within the Sea of Okhotsk, by the rigid core of the Sea of Okhotsk plate which is actually aseismic. Marginal parts of the plate are characterized by high tectonic and seismic activity (Kamchatka, Kuril Islands, Sakhalin, etc.). The exception is the aseismic “window’’ between the northern sector of Sakhalin and the Ketanda-Ul’beya zone in Priokhotye where local events are practically absent. 3 Conclusions The structural pattern of major seismogenic zones and the kinematics of motions in the focal zones of strong earthquakes within the Yana-Indigirka and the Indigirka-Kolyma (Okhotsk) segments suggest that active tectonic structures of the Chersky system are developing in transpression conditions which are caused by the convergence of the EU and NA plates (Grachev 1996, Imaev et al. 2000, Koz’min et al. 2001). The NE-SW pressure exerted by the NA plate on the EU plate led to the formation, in front of the Kolyma-Omolon block (indentor), of diverging NW-striking sinistral and SE-striking dextral strike slips with the transverse thrusts and reverse faults developed at their ends (Figs. 3, 4). Specificity of modern geodynamics of the CSZ is reflected in the structure of epicentral fields of local earthquakes. In the area experiencing the highest horizontal compression in front of the Kolyma-Omolon superterrane-indentor, there are the Andrei-Tas epicentral maximum (A on Fig. 3) and the epicentral band extending southwestward of it up to the Adycha River (C on Fig. 3). Earthquake clusters are detected on either side of the Andrei-Tas maximum at the periphery of the Chersky zone, where rocks are extruded to the north Polousny Range maximum (B on Fig.3) and southeast Upper Nera maximum (D on Fig.3). The general NE-SW sense of the superterrane motion (azimuth 50-85º) coincides with the orientation of the great axis of
isoseisms-ellipses constructed from observations of macroseismic effects of the Uyandina, Andrei-Tas and Ilin-Tas earthquakes (Imaeva et al., 2011, Koz’min et al. 2013). It is noteworthy that simultaneous formation of right-lateral and left-lateral strike slip faults on either side of the indentor is typical of many collisional zones. An example is provided by the well-studied structures in the Alpine-Himalayan belt, which resulted from horizontal extrusion of rock masses (Kopp 1997; Leonov et al. 2009, Trifonov et al. 2002). It is noted that in the areas of horizontal compression, the material being squeezed moves along an orogenic belt toward domains of lesser compression. As a result of the crustal material transportation, orogenic belts widen and transverse folded zones are forming. It is not impossible that thinning of the Earth’s crust to 35 km under the whole of the Chersky Range system to the west of the Moma-Selennyakh basin system (Suvorov and Kornilova 1986, Mackey et al. 1998, Fujita et al. 2009) (Fig. 5) is caused by extension resulted from upward-directed extrusion of rocks and subsequent lateral motions of separate slabs (blocks) in the opposite direction. A high heat flow up to 84 mW/m2 is recorded in the area of thinned crust (Catalogue…, 1985; Parfenov et al., 1988). A similar situation is observed in the Yana-Indigirka segment of the CSZ, in the area between the Yana and Indigirka Rivers (Fig. 3). In the mid-Indigirka River, under the pressure of the indentor, zones of fault influence get narrow, while northward and southward of the narrowing the fault zones widen to cover much space. One can see on space photos (Google site) that some of the slabs move N and NW toward the Polousny Range and the Kular Ridge. As a result of the slabs contact with the structures of the Polousny Range, dextral and sinistral strike slips are forming at the slabs boundaries. This supports the tendency of squeezing out the rock masses. Fig 6 shows initial extrusion of the Buordakh granitoid massif and its subsequent motion to W and NW. It is proved by the deformation of young fluvioglacial deposits by reverse faults and thrusts in the frontal (northwestern) part of the Buordakh massif as derived from large-scale (M: 200 000) geologic surveying in this region.
The convergence of NA and EU causes lateral compression and south-directed extrusion of the Okhotsk plate. This leads to the development of left-lateral strike slips in the northwestern segment and southeastern termination of the Chersky zone and in Shelikhov Bay of the Sea of Okhotsk as well as right-lateral strike slips in the river basins of Ketanda, Ul’beya and Okhota in Northern Priokhotye and Sakhalin Island [Mackey et al. 1998, Fujita et al. 2009]. The results of detailed seismotectonic studies and structural-dynamic models of major seismogenic zones of the Arctic-Asian seismic belt may serve as a basis for general seismic zoning of the CSZ, paleodynamic reconstructions, and search for mineral deposits. ACKNOWLEDGMENTS The authors are grateful to G.S. Gusev from the Institute of Mineralogy, Geochemistry and Crystal Chemistry of Rare Elements (Mosсow) - the Patriarch of the Yakut geology and, perhaps, the most prominent expert on tectonics and geodynamics of northeast Russia, for ongoing consultations on the geology and tectonics of the considered regions. The authors thank also O.P. Smekalin from the Institute of the Earth Crust, RAS for the fruitful comments and helpful remarks he made after reading the manuscript and E.V. Alekseenko from the Diamond and Precious Metal Geology Institute, RAS for translating the paper into English. This work was supported by the grant of the Ministry of Education and Sciences of the Russian Federation (State task in the field of scientific activity N 5.1771.2014/K) and the grant of the Russian Scientific Fund, project N 15-17-20000 “ Studies of the arctic segment of Chersky seismotectonic zone”. References Catalogue of data on heat flow in Siberia (1985). Duchkov, A.D., ed., Novosibirsk, Izd-vo IGIG SO AN SSSR., Nauka, 82 pp. (in Russian). Chapman M.B., Solomon S.C. (1976) North American-Eurasian plate boundary in Northeast Asia. Geophys. Res. V.81, N 5: 921–930.
Fujita K., Kozmin B.M., Mackey K.G. et al (2009) Seismotectonics of the Chersky seismic belt, eastern Russia (Yakutia) and Magadan district, Russia In: Geology, geophysics and tectonics of Northeastern Russia: a tribute to Leonid Parfenov. Editors: D.B.Stone, K.Fujita, P.W. Layer, E.L. Miller, A.V.Prokopiev, and J.Toro. Stephan Mueller Spec. Publ. (Ser., 4): 117–145. Grachev, A.F. (1996) Main problems of modern tectonics and geodynamics of northern Eurasia. Physics of the Earth N12: 5-36 (in Russian). Gusev, G.S. (1979) Fold structures and faults of the Verkhoyansk-Kolyma system of Mesozoides. Nauka, Moscow, 207 pp. (in Russian). Imaev, V.S., Imaeva, L.P., Koz’min, B.M. (1990) Active faults and seismotectonics of northeast Yakutia. Yakutian Science Center, Yakutsk, 138 pp. (in Russian). Imaev, V.S., Imaeva, L.P., Koz’min, B.M. (2000) Seismotectonics of Yakutia. GEOS, Moscow, 226 pp. (in Russian). Imaev, V.S., Imaeva, L.P., Mackey, K.G. et al (2009) Geodynamics of some segments of lithospheric plates in northeast Asia. Geophys. Res., V.10, N1: 5-17 (in Russian). Imaeva, L.P., Koz’min, B.M., Imaev, V.S. (2009). Seismotectonics of the northeastern segment of the Chersky Range zone. Otechestvennaya Geol N5: 94-100 (in Russian). Imaeva, L.P., Imaev, V.S., Koz’min, BM. (2010) Seismotectonic analysis of the Yana-Indigirka segment of the Chersky zone. Phys Earth N12: 79-86 (in Russian). Imaeva, L.P., Koz’min, B.M., Imaev, V.S. (2011) Dynamics of the focal zones of strong earthquakes on the northeastern flank of the Moma-Selennyakh basins. Otechestvennaya Geol N5:. 113-119 (in Russian).
Kopp, M.L. (1997) Lateral squeezing-out structures in the Alpian-Himalayan collisional belt. Nauchny mir, Moscow, 313 pp. (in Russian). Koz’min, B.M. (1984) Seismic belts of Yakutia and focal mechanisms of their earthquakes. Nauka, Moscow, 125 pp. (in Russian). Koz’min, B.M., Imaev, V.S., Imaeva, L.P. (2001) Seismicity and contemporary geodynamics. In: Tectonics, geodynamics and metallogeny of the Sakha Republic (Yakutia) territory. MAIK “Nauka”, Moscow, (in Russian). Koz’min, B.M., Shibaev, S.V., Imaeva, L.P., Imaev, V.S., Petrov, A.F., Timirshin, K.V. (2013) Present-day activity of seismic belts of Yakutia In: Continental rifting and accompanying processes. Materials of the 2d All-Russian Symposium with international participants. IZK SO RAN, Irkutsk, 167-171 (in Russian). Leonov, M.G., Kolodyazhny, S.Yu., Zykov, D.S. (2009) Within-plate structuralkinematic parageneses as indicators of lateral flows in the lithosphere of mobile belts and platforms In: Geodynamic evolution of the lithosphere of the Central Asian mobile belt (from ocean continentward). IZK SO RAN (V.1), Irkutsk, 170-173 (in Russian). Mackey, K. G., Fujita, K., Ruff, L. J. (1998) The crustal thickness of northeast Russia: Tectonophysics, V.284: 283-297. Mackey, K., Fujita, K., Hartse, H.E. et al. (2007) Seismicity of Eastern Russia 1960-2007: map, LAUR-04-1381. Moores, E.M., Twiss, R.J. (1995) Tectonics. W.H.Freeman and Company, New York, 415 pp.
Nokleberg, W.J., Parfenov, L.M., Monger, J.W.Y. et al. (2000), Phanerozoic tectonic evolution of the Circum-North Pacific // US Geological Survey Professional Paper 1626. – 122 p. Parfenov, L.M., Koz’min, B.M., Grinenko, O.V., Imaev,V.S., Imaeva, L.P. (1988) Geodynamics of the Chersky seismic belt. J. Geodynamics 9, 15–37. Parfenov, L.M. et al. (2001) A collage of terranes in the Verkhoyansk-Kolyma orogenic region In: Tectonics, geodynamics and metallogeny of the Sakha Republic (Yakutia) territory. MAIK “Nauka”, Moscow, 199254 (in Russian). Suvorov, V.D., Kornilova, Z.A. (1986) Thickness of the Earth’s crust in the southeastern Verkhoyansk-Kolyma region. Tikhookeanskaya geol N4: 32-35 (in Russian). Trifonov, V.G., Soboleva, O.V., Trifonov, R.V., Vostrikov, G.A. (2002) Contemporary geodynamics of the Alpian-Himalayan collisional belt. Transactions of GIN RAN. Issue 541. GEOS. Moscow, 225pp. (in Russian).
Figure captions to the paper “Structural-dynamic model of the Chersky seismotectonic zone (continental part of the Arctic-Asian seismic belt)
Fig. 1. Map of earthquake epicenters within the Chersky seismotectonic zone. Based on the materials of the RAS and SB RAS Geophysical Surveys (http://www.ceme.gsras.ru , URL://ftp.gsras.ru/pub/Teleseismic_bulletin) and International Seismological Centre (http://www.isc.as.uk). 1, boundaries of the Yana-Indigirka and Indigirka-Kolyma segments; 2, sence of motion of lithospheric plates. Outset shows kinematics of recent lithospheric plate in Northeast Asia and location of Arctic-Asian seismic belt. The study area is shown in box.
Fig. 2. Tectonic setting and composite stratigraphic section of the Yana – Indigirka segment (modified from Parfenov et al., 2001). Terranes: 1, Nagondzha (KNG); 2, Polousny-Debin (KPD); 3, Omulevka (KOV): Sl-Selennyach block, TS- Khayakhtakh block; 4, Munilkan (KMN); 5, Kular-Nera (slate belt) (KN). Postamalgamation deposits: 6, Late Jurassic volcanic- sedimentary of the Uyandina-Yasachnaya magnetic arc; 7, Late Yurassic shales of the Ilin-Tas anticlinorium. Post-accretionary overlying and stitching deposits: 8, Early Cretaceous granitoids; 9, Aptian-Early Cretaceous volcanic rocks; 10, Cenozoic rocks; 11, strike-slip faults; 12, normal faults; 13, thrusts (circled names): TR -Tirekhtyakh, NL - Nal’chan, PL - Polousny, ST –Setakchan, CI – Charky-Indigirka. Stereograms show focal mechanisms of earthquakes.
Fig. 3. Modern dynamics and distribution of earthquake epicenters in the Yana-Indigirka segment of the Chersky seismotectonic zone (modified from Imaeva et al., 2009; 2011).
1–2, Active faults: 1 strike-slip fault, 2 thrust and reverse fault; 3, sense of block motion; 4, focal mechanism stereograms, with date and magnitude of events, compressional quadrants of focal mechanisms are shaded; 5, sense of plate motions; 6, Balagan-Tas volcano; 7, magnitude of earthquakes (M), respectively: ≤3, 3.5, 4, 4.5, 5, 5.5, 6, ≥6.5. Seismicity maximums: A, AndreiTas; B, Polousny; C, Adycha; D, Upper Nera. Outset shows simplified model of the indentor (after Moores and Twiss, 1995). Plates: NA – North American, EU– Eurasian.
Fig. 4. Scheme of active faults of the Chersky seismotectonic zone. 1, faults abbreviations (circled numbers): 1 – Lena -Anabar suture, 2 – West Verkhoyansk suture, 3 – Central Verkhoyansk, 4 – East Verkhoyansk, 5 – Omoloy, 6 – Yana, 7 – Polousny, 8 – Selennyakh, 9 – Adycha-Taryn, 10 – Ilin-Tas, 11 – Arga-Tas, 12 – Myatis, 13 – Bryunganda, 14 – Nera and Chai-Yureya, 15 – Darpir, 16 – Ulakhan, 17 – Nel’kan-Kyllakh suture, 18 – Bilyakchan, 19 – Ketanda, 20 – Nyut-Ul’beya, 21– Chelomdza - Yama. Kinematics of faults: 2, strike-slip fault; 3, thrust and reverse; 4, normal fault; 5, unidentified fault. 6, focal mechanisms (stereograms), supporting kinematics of the faults; 7, Balagan-Tas volcano. Arrows indicate sense of plate motions.
Fig. 5. Crustal thickness within the Verkhoyansk-Kolyma system of Mesozoides (after Mackey et al. 1998) and heat flow manifestations (after Parfenov et al., 1988; Catalogue…,1985). 1, point-by-point heat flow measurements in mW/m2; 2, crustal thickness isolines in km; 3, area of crustal thinning; 1–6, Cenozoic basins (circled names): 1 Moma-Selennyakh, 2 Upper Nera, 3 Seimchan-Buyunda, 4 Upper Adycha, 5 Tuostakh, 6 Omoloy.
Fig. 6. Structural-kinematic pattern and sense of motion of the Buordakh massif rocks to the Chersky Range system on Landsat image from Google Earth site. Area of deformed fluvioglacial deposits is shown by dots.
Fig. 7. Structural-dynamic model of the Omulevka block. OK – Sea of Okhotsk plate, NA – North American plate. Arrows indicate the direction of regional compression based on geological-structural evidence and focal mechanism solutions of earthquakes (after Imaev et al., 2000).
Таble 1 Focal mechanism parameters for strong earthquakes in the zone of interaction of the Kolyma–Omolon block and Eurasian plate Date year:month :day
Origin (h:min)
Lat
Long
M
1951-02-12 1959-10-30 1962-04-19 1968-09-09 1970-06-05 1971-05-18 1971-09-30 1972-01-13 1974-06-19 1976-01-21 1979-10-07 1981-08-29 1982-09-03 1983-03-25 1984-11-22 1985-06-24 1987-02-11 1999-01-07 2005-01-25 2006-10-19 2008-06-22 2013-01-20 2013-02-14 2013-05-10
17-22 04-00 23-16 02-20 10-31 22-44 21-31 17-24 03-09 06-02 01-29 22-24 07-29 10-37 13-53 03-55 00-58 18-14 22-22 07-16 22-57 10-48 13-13 08-38
65.0 66.0 69.5 66.2 63.3 64.0 61.6 61.9 63.2 67.7 65.0 65.5 66.9 63.6 68.5 65.3 62.8 67.6 69.8 64.1 67.7 64.9 67.6 67.5
137.0 137.5 138.5 142.1 146.2 146.1 140.4 147.0 151.0 140.2 144.0 136.4 133.3 149.9 140.8 144.7 156.9 140.9 138.3 148.9 141.3 146.7 142.5 139.3
6.4 5.2 6.2 5.0 5.4 6.6 5.5 5.3 4.9 5.0 4.8 4.7 4.5 4.7 5.1 4.6 4.9 5.2 4.5 5.2 6.1 5.7 6.9 5.4
s1 Azm 80 151 130 154 172 16 309 10 313 304 101 72 144 288 148 04 309 112 356 313 355 324 37
s2 Pl 67 90 83 43 30 09 00 02 08 27 69 28 05 69 31 44 48 06 21 31 50 30 76 74
Azm 316 320 292 300 346 334 283 44 236 163 120 245 177 298 79 304 274 59 332 139 131 150 129 127
s3 Pl 13 00 06 46 60 80 88 60 78 58 21 57 67 18 56 44 00 74 64 53 40 57 13 0
Azm 222 230 22 38 247 82 107 219 101 50 211 03 339 32 190 46 184 218 208 254 222 258 220 217
Pl 19 00 05 07 06 03 01 29 08 14 02 17 20 09 14 12 42 15 16 18 01 12 3 14
Type of motion
Reference
REV REV REV REV-ST ST ST ST ST ST ST-REV REV ST ST REV ST-REV ST-REV REV ST ST-REV ST ST-REV ST THR THR
FUJ FUJ FUJ FUJ KOZ, FUJ KOZ, FUJ KOZ, FUJ KOZ, FUJ KOZ, FUJ KOZ, FUJ FUJ, KOZM FUJ, KOZM FUJ, KOZM FUJ, KOZM FUJ, ISC FUJ, KOZM FUJ FUJ, KOZM ISC, FUJ ISC, FUJ ISC, FUJ CMT CMT CMT
NOTES: Date and origin time given in GMT. Latitude in degrees north, longitude in degrees east. Magnitude is ISC MS or mb otherwise. s1, s2, s3 – tensile, intermediate and compressive stresses, respectively (Azm – stress axis azimuth, Pl – dip angle in degrees). Type of motion: REV- reverse, THR – thrust, ST – strike slip, REV- ST –reverse with strike slip component, STREV – strike slip with reverse component. Reference: FUJ – Fujita et al. (2009), KOZ – Koz’min (1984), KOZM – Koz’min et al. (2001), ISC – (http://www.isc.as.uk), CMT – (http://www.globalcmt.org/CMTsearch.html).
Table 2 Macroseismic characteristics of strong earthquakes within Chersky seismotectonic zone Date Lat Long M I0 Form of Direction of great S year:month:day isoseims axis of isoseims 1951-02-12 65.0 137.0 6.4 8-9 circle – ~400 1962-04-19 69.5 138.5 6.2 7-8 ellipse NW–SE 170 1970-06-05 63.3 146.2 5.4 7 – – ~100 1971-05-18 64.0 146.1 7.0 9 ellipse NW–SE 900 1971-09-30 61.6 140.4 5.5 7 ellipse meridional 200 1972-01-13 61.9 147.0 5.3 7 ellipse NW–SE 200 1974-06-19 63.2 151.0 4.9 6-7 ellipse NW–SE 160 1984-11-22 68.5 140.8 5.1 7 ellipse 120 NE–SW 2005-01-25 69.8 138.3 4.5 6 ellipse NW–SE ~50 2006-10-19 64.1 148.9 5.2 7 ellipse NW–SE 220 2008-06-22 67.7 141.3 6.6 8 ellipse 310 NE–SW 2013-01-20 64.9 146.7 5.7 7-8 ellipse NW–SE 300 2013-02-14 67.6 142.5 6.9 9 ellipse 500 NE–SW NOTES: Date and origin time given in GMT. Latitude in degrees north, longitude in degrees east. Magnitude is ISC MS or mb otherwise. I0 – epicentral intensity (Scale MM). S – maximal isoseismal area with intensity II–III in thous. km2.
Highlights 1.
We analyzed the structural-tectonic setting, the parameters of the deep structure, the kinematic types of seismogenic structures and morphotectonics features of the present topography and the corresponding field tectonic stresses, determined on the basis of the decisions of the focal mechanisms of local earthquakes.
2. Create a model of modern geodynamics of the seismotectonic zones Chersky (the continental part of Arktika-Asian seismic belt)
3. We found that within the regional segments of the Central part of the seismotectonic zones Chersky (the Yana-Indigirka and Indigirka-Kolyma), in the context of transpression (compression, strike-slip faults), initiated by the interaction of the frontal structures of the areas of the contact pair of the Eurasian and North American lithospheric plates.
4. As a consequence a number of different terranes geodynamic nature are subjected to horizontal compression where the individual segments according to the system of conjugated multidirectional strike-slips faults.
5.
A number of terranes that form the basis of Chersky seismic zone , experience in recent horizontal compression, which forms a conjugated system reseparating ( left and right) strike-slip faults.
S1367-9120(15)30139-5 http://dx.doi.org/10.1016/j.jseaes.2015.11.010 JAES 2563
To appear in:
Journal of Asian Earth Sciences
Received Date: Revised Date: Accepted Date:
21 April 2015 15 October 2015 13 November 2015
Please cite this article as: Imaeva, L.P., Imaev, V.S., Koz’min, B.M., Structural–Dynamic Model of The Chersky Seismotectonic Zone (Continental Part of The Arctic–Asian Seismic Belt), Journal of Asian Earth Sciences (2015), doi: http://dx.doi.org/10.1016/j.jseaes.2015.11.010
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STRUCTURAL–DYNAMIC MODEL OF THE CHERSKY SEISMOTECTONIC ZONE (CONTINENTAL PART OF THE ARCTIC–ASIAN SEISMIC BELT) L.P. Imaeva1, V.S. Imaev1, 3, B.M. Koz’min2
1
Institute of the Earth’s Crust, Siberian Division, Russian Academy of Sciences, 128
Lermontova St., Irkutsk 664033, Russia 2
Diamond and Precious Metal Geology Institute, Siberian Division, Russian Academy of
Sciences, 39 Lenin Prospekt, Yakutsk, Sakha Republic (Yakutia), 677891, Russia 3
Technical Institute (Branch) of the North Eastern Federal University, 16 Kravchenko,
Neryungri 678960, Russia
Abstract To construct a model for modern geodynamics of the Chersky seismotectonic zone (continental part of the Arctic-Asian seismic belt) we analyzed the available data on its structural-tectonic setting, depth structure, kinematics of active faults, morphotectonic features of modern topography, tectonic stress fields as derived from the earthquake focal mechanisms as well as the types of Late Cenozoic fold and rupture deformation. It is established that the YanaIndigirka and Indigirka-Kolyma segments in the central part of the Chersky zone underwent transpression due to collision of the Eurasian (EU) and North American (NA) lithospheric plates. This was only possible if, in course of the plate convergence, the Kolyma-Omolon block in the frontal part of the NA plate formed the active indentor. Under the block pressure, geodynamic settings experience horizontal compression, in which case some of the blocks are being extruded along the system of northwestern and southeastern strike-slip faults. This results in the formation of major seismogenic structures with a high seismic potential in the marginal and frontal parts of the Chersky zone.
Keywords: Arctic-Asian seismic belt, Chersky seismotectonic zone, Kolyma-Omolon block, active fault, earthquake focal mechanism, type of Late Cenozoic deformations, indentor, structural-dynamic model.
1 Introduction Combined geological-geophysical and seismological studies in northeast Asia revealed the extensive Arctic-Asian seismic belt (AASB) (Fig. 1), which marks the boundary between the major North American and Eurasian lithospheric plates (Chapmen and Solomon 1976, Imaev et al. 2000, Fujita et al. 2009). Geodynamic processes occurring within the belt cause seismotectonic deformation of the Earth’s crust in the zone of contact between the plates. Tectonically, the AASB can be divided into major regional segments (Laptev Sea, Kharaulakh, Chersky, and Sea of Okhotsk) (Imaev et al. 1990). Structural paragenesis of active faults developed in the segments is controlled by the stress state of the Earth’s crust (Imaev et al. 2000, 2009, Koz’min et al. 2001). Instrumental seismic observations conducted by Geophysical Surveys of Russian Academy of Sciences and its Siberian Branch (http://www.ceme.gsras.ru) and the Michigan State University (USA) (Mackey et al. 2007) in northeast Russia, and available geological-structural (Parfenov et al. 2001) and morphotectonic (Imaeva et al. 2009) data helped elucidate the dynamics of seismogenic structures of constituent segments of the Chersky seismotectonic zone (CSZ) and develop a regional structural-dynamic model. The investigations were aimed at: -
analyzing
the
published
structural-tectonic,
geological-geophysical
and
seismological data and compiling additional morphotectonic maps for the region; -
estimating effect of reactivated Late Mesozoic structures on Cenozoic tectonics and modern structural pattern;
-
making structural-dynamic analysis of the strong earthquakes epicentral zones and refining the kinematics of active faults;
-
elucidating the kinematics of motions and developing regional structural-dynamic models of major seismogenic structures in some CSZ segments.
Below two local segments within Mesozoides of the CSZ, which are the Yana-Indigirka and Indigirka-Kolyma (Okhotsk) segments, are considered. Their location is shown in Fig.1. The segments were recognized by specific structural paragenesis of active faults characteristic of certain types of crustal stress state (Gusev 1979, Imaeva et al. 2011, Parfenov et al. 2001), geophysical field structures (Suvorov and Kornilova 1986, Imaev et al. 2000), morphotectonic features (Imaev et al. 2000, 2009) and dynamics of major seismogenic structures (Imaev et al. 2009, Imaeva et al. 2009) of the segments.
2 The Yana-Indigirka segment The segment is represented, morphotectonically, by deformation structures developed on the northern and northwestern flanks of the frontal zone of interaction between the EU and NA plates (Fig. 2). Their zone of collision has specific deep structure (Suvorov and Kornilova 1986, Imaev et al. 2000), representing a collage of terranes that originated under different geodynamic conditions (Parfenov et al. 2001) and are characterized by a specific morphotectonic complex of faults and blocks (Imaev et al. 2000, 2009). Tectonically, the segment includes frontal zones of the Kolyma-Omolon block and a number of terranes (Polousny-Debin, Omulevka, Nagodzha, etc.) of different geodynamic nature located to the north and northwest of the sharp eastward bend of the Indigirka River (Fig. 2). The terranes are broken by a series of northwestern faults mostly of left-lateral strike-slip kinematics into some blocks (Imaev et al. 2000, Imaeva et al. 2011), of which the largest are TasKhayakhtakh and Selennyakh (Fig. 2). Late Mesozoic faults, which were reactivated in the Cenozoic, played a decisive role in shaping the modern topography of the Yana-Indigirka segment. Analysis of the kinematics of active faults and deformation of Cenozoic deposits in the northeastern flank of the Yana-
Indigirka segment (Imaev et al. 2000, 2009, Imaeva et al. 2009, 2010) showed they are mostly thrust, reverse and strike slip faults. The amount of horizontal displacement along these faults is estimated at a few tens of kilometers (Gusev 1979). Most representative for analyzing the dynamics of the formation of seismogenic structures in the segment is the fault system traceable along the axial part of the Moma Ridge within the Ilin-Tas folded zone (Fig. 3). In plan view, the southern sides of the Ilin-Tas leftlateral and the Arga-Tas right-lateral strike slip faults (Fig.4, Nos.10 and 11) join at an obtuse angle at about the center of the Moma Ridge. To the northwest and southeast of their contact zone there are fan-like zones of compression represented by folds in Cenozoic rocks of the Indigirka-Zyryanka basin and the Moma-Selennyakh depressions (Imaev et al. 2000, 2009, Imaeva et al. 2009, 2011). In front of the junction of the faults a zone of extension occurs, which is morphologically expressed as a sublatitudinal valley of the mid-Moma River. This is evidenced indirectly by the presence there of the Balagan-Tas volcano of Cenozoic age, the world’s largest Moma icing and numerous mineralized thermal groundwater springs (Grachev 1996). The stress state of the Earth’s crust was determined from the focal mechanisms of earthquakes detected in the zone of interaction of the Kolyma-Omolon block and the Eurasian plate (Table 1). Analysis of active tectonic elements and seismic manifestations revealed that motions in the foci of strong earthquakes coincide with the kinematics of the active faults they are confined to. Characteristic of the earthquakes within the CSZ is that they all occur under conditions of stable NE-SW compression. The compressive stresses (σ 3) are subhorizontal (dip angles 3 to 44º), and they act across the strike of structural elements of the territory. Tensile stresses (σ1) often act along the fault lines and are oriented both horizontally and subvertically with respect to the Earth’s surface (dip angles 2 to 85°). The intermediate stress axes (σ 2) show random orientation in space and are inclined to the horizon at the angles of 0 to 82º. This stress
pattern is seen in the earthquake foci all the way from North Verkhoyansk to the Sea of Okhotsk (Figs. 3, 4). Orientation of major tectonic stresses as derived from seismological data confirms that motions in the earthquake foci within the CSZ are mostly reverse, thrust and strike slip faults. Out of 30 determinations, 39% are reverse faults, 30% strike slips, 17% thrusts and the rest (14%) is combination of strike slips and normal faults (Imaev et al. 2000, Koz’min et al. 2001). The data obtained indicate that seismic processes within the CSZ proceed under dominant compression with active development of reverse faults, strike slips and their combinations (Fig. 4). This is well evidenced by the structural patterns of major seismogenic areas over the entire CSZ. Specifically, the band of epicenters observed along the Ulakhan fault line (Fig. 4, N16) continues onto the left bank of the Indigirka River, and then at about 140º-141ºE it changes sharply its northwestern orientation to longitudinal one (Fig. 1). The band cuts across the strike of the Moma-Selennyakh basin system, and along the western slope of the Andrei-Tas Ridge where it can be traced up to the Polousny Range (Fig. 3) in the zone of influence of the Selennyakh fault (Fig. 4, No.8). In the Yana-Indigirka segment, several seismic activity maxima are recognized (Fig.3). The highest maximum occurs within the Andrei-Tas block where along with numerous weak shakes the 1984 Uyandina earthquake (intensity VII, M s =5.6), the 1999 event (intensity VI-VII, Ms =5.2); the 2008 Andrei-Tas event (intensity VIII, Ms =6.1) and the 2013 Ilin-Tas quake (intensity IX, Ms =6.9) have been reported (Figs. 2, 3). Isoseism maps were compiled for many of the strong earthquakes within the CSZ (Koz’min 1984, Imaev et al. 2000, Imaeva et al. 2011). The tendency observed here is that all isoseisms outlining areas of certain earthquake intensity have a form of an ellipse with its great axis elongated in a northwestern direction along the lines of major seismically active faults (Table 2). The exception is provided by isoseisms of earthquakes in the seismic maximum within the Andrei-Tas block (Imaeva et al. 2009, 2011).
It is established that isoseisms of earthquakes within the Andrei-Tas block crosscut active faults, in contrast to areas NW and SE of the block where isoseisms are elongated parallel to the faults. This may be explained by maximum pressure exerted by the Kolyma-Omolon block on the EU plate on the northeast (Figs. 1, 3). It is likely that here, in the zone of the EU and NA contact, compression causes accumulation of significant tectonic stresses resulting in activation of seismotectonic processes. The general sense of the movement of the Kolyma-Omolon block is determined from the spatial position of isoseisms which are, under the block effect, oriented NESW across the structural elements. This dynamic setting favored the formation, to the north and northwest of the area of maximum pressure of the block, of transverse zones of compression represented by a system of reverse faults and thrusts (Polousny region) and multiple folding episodes of folds on folds in Cenozoic deposits of the Indigirka-Zyryanka basin. Thus, under conditions of transpression, a specific dynamic setting has developed within the Yana-Indigirka segment as a result of interaction of frontal structures of the EU and NA plates at their boundary. Such dynamic setting is possible if the Kolyma-Omolon block joins the leading edge of the NA plate to become an active indentor during the plates convergence. This resulted in the formation, in front of the indentor, of diverging NW-striking sinistral and SEstriking dextral strike slips which developed, at their ends, systems of seismogenic reverse faults and thrusts with a maximum seismic potential.
3 The Indigirka-Kolyma (Okhotsk) segment-block The Indigirka-Kolyma block is a northern fragment of the Sea of Okhotsk crustal plate also known as a terrane under the same name (see Fig. 1). It occurs to the east of the southern sector of the Verkhoyansk fold-and-thrust belt from which it is separated by the right-striking KetandaUl’beya zone (Fig. 1 and Fig. 4, Nos.19 and 20). The basement of the Okhotsk terrane is made of Archean and Early Proterozoic crystalline schists and gneisses of the granulite and amphibolite
metamorphic facies (Gusev 1979, Leonov et al. 2009). Most of the terrane is covered by flatlying volcanites of the Okhotsk-Chukotka belt. Spatial distribution of seismicity permitted the recognition of three zones of high seismotectonic activity in the segment, where seismicity is clustered in extensive diffuse bands confined to the zones of influence of the faults bounding the Indigirka-Kolyma (Okhotsk) block on the west, northeast and south. In the first band (Fig. 1), the earthquake epicenters are concentrated along the sublongitudinal Ketanda-Ul’beya strike-slip fault system (Fig.4, Nos.19 and 20). Focal mechanisms of the events that occurred here in 1977, 1984 and 1986 point to the east-northeast orientation of compressive stresses and dextral strike-slip motions in their foci. The second seismic band is confined to the most active Ulakhan and Chai-Yureya faults (Fig 4, Nos.16 and 14) along which the largest seismic events were registered in the period from 1974 to 1992. Focal mechanism solutions indicate left-lateral strike-slip motions in the earthquake foci where compressive stresses are NE-SW oriented (Imaev et al. 2000, Koz’min et al. 2001). The third band (Fig. 1) is restricted to the zone of influence of the sublatitudinal Chelomdzha-Yama left-lateral strike slip with a reverse fault component (Fig. 4, No. 21). It extends along the northern coast of the Sea of Okhotsk. The focal mechanism of the 2001 earthquake with the epicenter located within this fault also corresponds to left-lateral motions in its focus. All of the above mentioned fault systems are well-defined in geophysical field maps. Most mobile is the northeast boundary of the Indigirka-Kolyma (Okhotsk) block (second band), which represents a zone of contact between the North American and the Sea of Okhotsk plates, and is confined to the southeast flank of the CSZ. A high earthquake density is also registered at the southern boundary of the block (third band) where the epicenters are traced along the northern shore of the Sea of Okhotsk to the western coast of Kamchatka and in the northern part of the Sea of Okhotsk floor. This band coincides with the thrust of the ancient
Benioff seismic zone (Nokleberg et al., 2000). The Ketanda-Ul’beya zone (first band) at the western boundary of the block is marked by a somewhat lower seismic activity. All events detected within the block are crustal in depth (up to 30 km) (Imaev et al. 2000, Koz’min et al. 2001). Focal mechanism parameters of strong earthquakes and kinematics of active faults developed within the discussed Indigirka-Kolyma block showed the prevalence of horizontal motions (Table 1). Vertical motions (reverse faults, thrusts, and normal faults) are subordinate. Most representative is the en-echelon system of strike-slip faults at the northeastern boundary of the block of which the most active is the Ulakhan fault. It forms a dynamic pair with the Darpir fault. Both faults are clearly visible on mid- and large-scale satellite images and aerial photographs, and are expressed as continuous straight lineaments of northwest strike on topographic maps. The Ulakhan fault and the Darpir fault (Fig. 4, Nos.16 and 15) meet at an angle of 20-25 o and bound the Omulevka block of Paleozoic rocks (elevated 450-550 m asl) surrounded by Mesozoic deposits (Fig. 4). The Omulevka block was squeezed out to the surface as a result of horizontal deformations (Fig. 7). The Ulakhan-Darpir dynamic pair most clearly demonstrates the type of deformation processes at the boundary of the North American and Sea of Okhotsk plates. According to present tectonic models, the Omulevka block is a separate terrane incorporated in the Mesozoic structural framework in the processes of collisional and postcollisional transformations of the structure of the Verkhoyansk-Kolyma Mesozoides (Parfenov et al., 2001). The activity of the Ulakhan fault and the Darpir fault is nowadays confirmed not only by numerous earthquake epicenters but also by a series of paleoseismic dislocations and presentday deformations of the Earth’s crust (landslides, rock-slides, rockfalls ets) found in the zones of influence of the faults (Imaev et al., 2000). The facts that the Omulevka block is bounded by the Ulakhan and Darpir strike-slip faults of opposing kinematics (Fig. 7), that its frontal part is
deformed by reverse faults and thrusts, and that a number of shallow small seismic events were recorded there all indicate that the block was formed by the detachment mechanism. The territory to the south of the Indigirka-Kolyma (Okhotsk) segment-block is represented, within the Sea of Okhotsk, by the rigid core of the Sea of Okhotsk plate which is actually aseismic. Marginal parts of the plate are characterized by high tectonic and seismic activity (Kamchatka, Kuril Islands, Sakhalin, etc.). The exception is the aseismic “window’’ between the northern sector of Sakhalin and the Ketanda-Ul’beya zone in Priokhotye where local events are practically absent. 3 Conclusions The structural pattern of major seismogenic zones and the kinematics of motions in the focal zones of strong earthquakes within the Yana-Indigirka and the Indigirka-Kolyma (Okhotsk) segments suggest that active tectonic structures of the Chersky system are developing in transpression conditions which are caused by the convergence of the EU and NA plates (Grachev 1996, Imaev et al. 2000, Koz’min et al. 2001). The NE-SW pressure exerted by the NA plate on the EU plate led to the formation, in front of the Kolyma-Omolon block (indentor), of diverging NW-striking sinistral and SE-striking dextral strike slips with the transverse thrusts and reverse faults developed at their ends (Figs. 3, 4). Specificity of modern geodynamics of the CSZ is reflected in the structure of epicentral fields of local earthquakes. In the area experiencing the highest horizontal compression in front of the Kolyma-Omolon superterrane-indentor, there are the Andrei-Tas epicentral maximum (A on Fig. 3) and the epicentral band extending southwestward of it up to the Adycha River (C on Fig. 3). Earthquake clusters are detected on either side of the Andrei-Tas maximum at the periphery of the Chersky zone, where rocks are extruded to the north Polousny Range maximum (B on Fig.3) and southeast Upper Nera maximum (D on Fig.3). The general NE-SW sense of the superterrane motion (azimuth 50-85º) coincides with the orientation of the great axis of
isoseisms-ellipses constructed from observations of macroseismic effects of the Uyandina, Andrei-Tas and Ilin-Tas earthquakes (Imaeva et al., 2011, Koz’min et al. 2013). It is noteworthy that simultaneous formation of right-lateral and left-lateral strike slip faults on either side of the indentor is typical of many collisional zones. An example is provided by the well-studied structures in the Alpine-Himalayan belt, which resulted from horizontal extrusion of rock masses (Kopp 1997; Leonov et al. 2009, Trifonov et al. 2002). It is noted that in the areas of horizontal compression, the material being squeezed moves along an orogenic belt toward domains of lesser compression. As a result of the crustal material transportation, orogenic belts widen and transverse folded zones are forming. It is not impossible that thinning of the Earth’s crust to 35 km under the whole of the Chersky Range system to the west of the Moma-Selennyakh basin system (Suvorov and Kornilova 1986, Mackey et al. 1998, Fujita et al. 2009) (Fig. 5) is caused by extension resulted from upward-directed extrusion of rocks and subsequent lateral motions of separate slabs (blocks) in the opposite direction. A high heat flow up to 84 mW/m2 is recorded in the area of thinned crust (Catalogue…, 1985; Parfenov et al., 1988). A similar situation is observed in the Yana-Indigirka segment of the CSZ, in the area between the Yana and Indigirka Rivers (Fig. 3). In the mid-Indigirka River, under the pressure of the indentor, zones of fault influence get narrow, while northward and southward of the narrowing the fault zones widen to cover much space. One can see on space photos (Google site) that some of the slabs move N and NW toward the Polousny Range and the Kular Ridge. As a result of the slabs contact with the structures of the Polousny Range, dextral and sinistral strike slips are forming at the slabs boundaries. This supports the tendency of squeezing out the rock masses. Fig 6 shows initial extrusion of the Buordakh granitoid massif and its subsequent motion to W and NW. It is proved by the deformation of young fluvioglacial deposits by reverse faults and thrusts in the frontal (northwestern) part of the Buordakh massif as derived from large-scale (M: 200 000) geologic surveying in this region.
The convergence of NA and EU causes lateral compression and south-directed extrusion of the Okhotsk plate. This leads to the development of left-lateral strike slips in the northwestern segment and southeastern termination of the Chersky zone and in Shelikhov Bay of the Sea of Okhotsk as well as right-lateral strike slips in the river basins of Ketanda, Ul’beya and Okhota in Northern Priokhotye and Sakhalin Island [Mackey et al. 1998, Fujita et al. 2009]. The results of detailed seismotectonic studies and structural-dynamic models of major seismogenic zones of the Arctic-Asian seismic belt may serve as a basis for general seismic zoning of the CSZ, paleodynamic reconstructions, and search for mineral deposits. ACKNOWLEDGMENTS The authors are grateful to G.S. Gusev from the Institute of Mineralogy, Geochemistry and Crystal Chemistry of Rare Elements (Mosсow) - the Patriarch of the Yakut geology and, perhaps, the most prominent expert on tectonics and geodynamics of northeast Russia, for ongoing consultations on the geology and tectonics of the considered regions. The authors thank also O.P. Smekalin from the Institute of the Earth Crust, RAS for the fruitful comments and helpful remarks he made after reading the manuscript and E.V. Alekseenko from the Diamond and Precious Metal Geology Institute, RAS for translating the paper into English. This work was supported by the grant of the Ministry of Education and Sciences of the Russian Federation (State task in the field of scientific activity N 5.1771.2014/K) and the grant of the Russian Scientific Fund, project N 15-17-20000 “ Studies of the arctic segment of Chersky seismotectonic zone”. References Catalogue of data on heat flow in Siberia (1985). Duchkov, A.D., ed., Novosibirsk, Izd-vo IGIG SO AN SSSR., Nauka, 82 pp. (in Russian). Chapman M.B., Solomon S.C. (1976) North American-Eurasian plate boundary in Northeast Asia. Geophys. Res. V.81, N 5: 921–930.
Fujita K., Kozmin B.M., Mackey K.G. et al (2009) Seismotectonics of the Chersky seismic belt, eastern Russia (Yakutia) and Magadan district, Russia In: Geology, geophysics and tectonics of Northeastern Russia: a tribute to Leonid Parfenov. Editors: D.B.Stone, K.Fujita, P.W. Layer, E.L. Miller, A.V.Prokopiev, and J.Toro. Stephan Mueller Spec. Publ. (Ser., 4): 117–145. Grachev, A.F. (1996) Main problems of modern tectonics and geodynamics of northern Eurasia. Physics of the Earth N12: 5-36 (in Russian). Gusev, G.S. (1979) Fold structures and faults of the Verkhoyansk-Kolyma system of Mesozoides. Nauka, Moscow, 207 pp. (in Russian). Imaev, V.S., Imaeva, L.P., Koz’min, B.M. (1990) Active faults and seismotectonics of northeast Yakutia. Yakutian Science Center, Yakutsk, 138 pp. (in Russian). Imaev, V.S., Imaeva, L.P., Koz’min, B.M. (2000) Seismotectonics of Yakutia. GEOS, Moscow, 226 pp. (in Russian). Imaev, V.S., Imaeva, L.P., Mackey, K.G. et al (2009) Geodynamics of some segments of lithospheric plates in northeast Asia. Geophys. Res., V.10, N1: 5-17 (in Russian). Imaeva, L.P., Koz’min, B.M., Imaev, V.S. (2009). Seismotectonics of the northeastern segment of the Chersky Range zone. Otechestvennaya Geol N5: 94-100 (in Russian). Imaeva, L.P., Imaev, V.S., Koz’min, BM. (2010) Seismotectonic analysis of the Yana-Indigirka segment of the Chersky zone. Phys Earth N12: 79-86 (in Russian). Imaeva, L.P., Koz’min, B.M., Imaev, V.S. (2011) Dynamics of the focal zones of strong earthquakes on the northeastern flank of the Moma-Selennyakh basins. Otechestvennaya Geol N5:. 113-119 (in Russian).
Kopp, M.L. (1997) Lateral squeezing-out structures in the Alpian-Himalayan collisional belt. Nauchny mir, Moscow, 313 pp. (in Russian). Koz’min, B.M. (1984) Seismic belts of Yakutia and focal mechanisms of their earthquakes. Nauka, Moscow, 125 pp. (in Russian). Koz’min, B.M., Imaev, V.S., Imaeva, L.P. (2001) Seismicity and contemporary geodynamics. In: Tectonics, geodynamics and metallogeny of the Sakha Republic (Yakutia) territory. MAIK “Nauka”, Moscow, (in Russian). Koz’min, B.M., Shibaev, S.V., Imaeva, L.P., Imaev, V.S., Petrov, A.F., Timirshin, K.V. (2013) Present-day activity of seismic belts of Yakutia In: Continental rifting and accompanying processes. Materials of the 2d All-Russian Symposium with international participants. IZK SO RAN, Irkutsk, 167-171 (in Russian). Leonov, M.G., Kolodyazhny, S.Yu., Zykov, D.S. (2009) Within-plate structuralkinematic parageneses as indicators of lateral flows in the lithosphere of mobile belts and platforms In: Geodynamic evolution of the lithosphere of the Central Asian mobile belt (from ocean continentward). IZK SO RAN (V.1), Irkutsk, 170-173 (in Russian). Mackey, K. G., Fujita, K., Ruff, L. J. (1998) The crustal thickness of northeast Russia: Tectonophysics, V.284: 283-297. Mackey, K., Fujita, K., Hartse, H.E. et al. (2007) Seismicity of Eastern Russia 1960-2007: map, LAUR-04-1381. Moores, E.M., Twiss, R.J. (1995) Tectonics. W.H.Freeman and Company, New York, 415 pp.
Nokleberg, W.J., Parfenov, L.M., Monger, J.W.Y. et al. (2000), Phanerozoic tectonic evolution of the Circum-North Pacific // US Geological Survey Professional Paper 1626. – 122 p. Parfenov, L.M., Koz’min, B.M., Grinenko, O.V., Imaev,V.S., Imaeva, L.P. (1988) Geodynamics of the Chersky seismic belt. J. Geodynamics 9, 15–37. Parfenov, L.M. et al. (2001) A collage of terranes in the Verkhoyansk-Kolyma orogenic region In: Tectonics, geodynamics and metallogeny of the Sakha Republic (Yakutia) territory. MAIK “Nauka”, Moscow, 199254 (in Russian). Suvorov, V.D., Kornilova, Z.A. (1986) Thickness of the Earth’s crust in the southeastern Verkhoyansk-Kolyma region. Tikhookeanskaya geol N4: 32-35 (in Russian). Trifonov, V.G., Soboleva, O.V., Trifonov, R.V., Vostrikov, G.A. (2002) Contemporary geodynamics of the Alpian-Himalayan collisional belt. Transactions of GIN RAN. Issue 541. GEOS. Moscow, 225pp. (in Russian).
Figure captions to the paper “Structural-dynamic model of the Chersky seismotectonic zone (continental part of the Arctic-Asian seismic belt)
Fig. 1. Map of earthquake epicenters within the Chersky seismotectonic zone. Based on the materials of the RAS and SB RAS Geophysical Surveys (http://www.ceme.gsras.ru , URL://ftp.gsras.ru/pub/Teleseismic_bulletin) and International Seismological Centre (http://www.isc.as.uk). 1, boundaries of the Yana-Indigirka and Indigirka-Kolyma segments; 2, sence of motion of lithospheric plates. Outset shows kinematics of recent lithospheric plate in Northeast Asia and location of Arctic-Asian seismic belt. The study area is shown in box.
Fig. 2. Tectonic setting and composite stratigraphic section of the Yana – Indigirka segment (modified from Parfenov et al., 2001). Terranes: 1, Nagondzha (KNG); 2, Polousny-Debin (KPD); 3, Omulevka (KOV): Sl-Selennyach block, TS- Khayakhtakh block; 4, Munilkan (KMN); 5, Kular-Nera (slate belt) (KN). Postamalgamation deposits: 6, Late Jurassic volcanic- sedimentary of the Uyandina-Yasachnaya magnetic arc; 7, Late Yurassic shales of the Ilin-Tas anticlinorium. Post-accretionary overlying and stitching deposits: 8, Early Cretaceous granitoids; 9, Aptian-Early Cretaceous volcanic rocks; 10, Cenozoic rocks; 11, strike-slip faults; 12, normal faults; 13, thrusts (circled names): TR -Tirekhtyakh, NL - Nal’chan, PL - Polousny, ST –Setakchan, CI – Charky-Indigirka. Stereograms show focal mechanisms of earthquakes.
Fig. 3. Modern dynamics and distribution of earthquake epicenters in the Yana-Indigirka segment of the Chersky seismotectonic zone (modified from Imaeva et al., 2009; 2011).
1–2, Active faults: 1 strike-slip fault, 2 thrust and reverse fault; 3, sense of block motion; 4, focal mechanism stereograms, with date and magnitude of events, compressional quadrants of focal mechanisms are shaded; 5, sense of plate motions; 6, Balagan-Tas volcano; 7, magnitude of earthquakes (M), respectively: ≤3, 3.5, 4, 4.5, 5, 5.5, 6, ≥6.5. Seismicity maximums: A, AndreiTas; B, Polousny; C, Adycha; D, Upper Nera. Outset shows simplified model of the indentor (after Moores and Twiss, 1995). Plates: NA – North American, EU– Eurasian.
Fig. 4. Scheme of active faults of the Chersky seismotectonic zone. 1, faults abbreviations (circled numbers): 1 – Lena -Anabar suture, 2 – West Verkhoyansk suture, 3 – Central Verkhoyansk, 4 – East Verkhoyansk, 5 – Omoloy, 6 – Yana, 7 – Polousny, 8 – Selennyakh, 9 – Adycha-Taryn, 10 – Ilin-Tas, 11 – Arga-Tas, 12 – Myatis, 13 – Bryunganda, 14 – Nera and Chai-Yureya, 15 – Darpir, 16 – Ulakhan, 17 – Nel’kan-Kyllakh suture, 18 – Bilyakchan, 19 – Ketanda, 20 – Nyut-Ul’beya, 21– Chelomdza - Yama. Kinematics of faults: 2, strike-slip fault; 3, thrust and reverse; 4, normal fault; 5, unidentified fault. 6, focal mechanisms (stereograms), supporting kinematics of the faults; 7, Balagan-Tas volcano. Arrows indicate sense of plate motions.
Fig. 5. Crustal thickness within the Verkhoyansk-Kolyma system of Mesozoides (after Mackey et al. 1998) and heat flow manifestations (after Parfenov et al., 1988; Catalogue…,1985). 1, point-by-point heat flow measurements in mW/m2; 2, crustal thickness isolines in km; 3, area of crustal thinning; 1–6, Cenozoic basins (circled names): 1 Moma-Selennyakh, 2 Upper Nera, 3 Seimchan-Buyunda, 4 Upper Adycha, 5 Tuostakh, 6 Omoloy.
Fig. 6. Structural-kinematic pattern and sense of motion of the Buordakh massif rocks to the Chersky Range system on Landsat image from Google Earth site. Area of deformed fluvioglacial deposits is shown by dots.
Fig. 7. Structural-dynamic model of the Omulevka block. OK – Sea of Okhotsk plate, NA – North American plate. Arrows indicate the direction of regional compression based on geological-structural evidence and focal mechanism solutions of earthquakes (after Imaev et al., 2000).
Таble 1 Focal mechanism parameters for strong earthquakes in the zone of interaction of the Kolyma–Omolon block and Eurasian plate Date year:month :day
Origin (h:min)
Lat
Long
M
1951-02-12 1959-10-30 1962-04-19 1968-09-09 1970-06-05 1971-05-18 1971-09-30 1972-01-13 1974-06-19 1976-01-21 1979-10-07 1981-08-29 1982-09-03 1983-03-25 1984-11-22 1985-06-24 1987-02-11 1999-01-07 2005-01-25 2006-10-19 2008-06-22 2013-01-20 2013-02-14 2013-05-10
17-22 04-00 23-16 02-20 10-31 22-44 21-31 17-24 03-09 06-02 01-29 22-24 07-29 10-37 13-53 03-55 00-58 18-14 22-22 07-16 22-57 10-48 13-13 08-38
65.0 66.0 69.5 66.2 63.3 64.0 61.6 61.9 63.2 67.7 65.0 65.5 66.9 63.6 68.5 65.3 62.8 67.6 69.8 64.1 67.7 64.9 67.6 67.5
137.0 137.5 138.5 142.1 146.2 146.1 140.4 147.0 151.0 140.2 144.0 136.4 133.3 149.9 140.8 144.7 156.9 140.9 138.3 148.9 141.3 146.7 142.5 139.3
6.4 5.2 6.2 5.0 5.4 6.6 5.5 5.3 4.9 5.0 4.8 4.7 4.5 4.7 5.1 4.6 4.9 5.2 4.5 5.2 6.1 5.7 6.9 5.4
s1 Azm 80 151 130 154 172 16 309 10 313 304 101 72 144 288 148 04 309 112 356 313 355 324 37
s2 Pl 67 90 83 43 30 09 00 02 08 27 69 28 05 69 31 44 48 06 21 31 50 30 76 74
Azm 316 320 292 300 346 334 283 44 236 163 120 245 177 298 79 304 274 59 332 139 131 150 129 127
s3 Pl 13 00 06 46 60 80 88 60 78 58 21 57 67 18 56 44 00 74 64 53 40 57 13 0
Azm 222 230 22 38 247 82 107 219 101 50 211 03 339 32 190 46 184 218 208 254 222 258 220 217
Pl 19 00 05 07 06 03 01 29 08 14 02 17 20 09 14 12 42 15 16 18 01 12 3 14
Type of motion
Reference
REV REV REV REV-ST ST ST ST ST ST ST-REV REV ST ST REV ST-REV ST-REV REV ST ST-REV ST ST-REV ST THR THR
FUJ FUJ FUJ FUJ KOZ, FUJ KOZ, FUJ KOZ, FUJ KOZ, FUJ KOZ, FUJ KOZ, FUJ FUJ, KOZM FUJ, KOZM FUJ, KOZM FUJ, KOZM FUJ, ISC FUJ, KOZM FUJ FUJ, KOZM ISC, FUJ ISC, FUJ ISC, FUJ CMT CMT CMT
NOTES: Date and origin time given in GMT. Latitude in degrees north, longitude in degrees east. Magnitude is ISC MS or mb otherwise. s1, s2, s3 – tensile, intermediate and compressive stresses, respectively (Azm – stress axis azimuth, Pl – dip angle in degrees). Type of motion: REV- reverse, THR – thrust, ST – strike slip, REV- ST –reverse with strike slip component, STREV – strike slip with reverse component. Reference: FUJ – Fujita et al. (2009), KOZ – Koz’min (1984), KOZM – Koz’min et al. (2001), ISC – (http://www.isc.as.uk), CMT – (http://www.globalcmt.org/CMTsearch.html).
Table 2 Macroseismic characteristics of strong earthquakes within Chersky seismotectonic zone Date Lat Long M I0 Form of Direction of great S year:month:day isoseims axis of isoseims 1951-02-12 65.0 137.0 6.4 8-9 circle – ~400 1962-04-19 69.5 138.5 6.2 7-8 ellipse NW–SE 170 1970-06-05 63.3 146.2 5.4 7 – – ~100 1971-05-18 64.0 146.1 7.0 9 ellipse NW–SE 900 1971-09-30 61.6 140.4 5.5 7 ellipse meridional 200 1972-01-13 61.9 147.0 5.3 7 ellipse NW–SE 200 1974-06-19 63.2 151.0 4.9 6-7 ellipse NW–SE 160 1984-11-22 68.5 140.8 5.1 7 ellipse 120 NE–SW 2005-01-25 69.8 138.3 4.5 6 ellipse NW–SE ~50 2006-10-19 64.1 148.9 5.2 7 ellipse NW–SE 220 2008-06-22 67.7 141.3 6.6 8 ellipse 310 NE–SW 2013-01-20 64.9 146.7 5.7 7-8 ellipse NW–SE 300 2013-02-14 67.6 142.5 6.9 9 ellipse 500 NE–SW NOTES: Date and origin time given in GMT. Latitude in degrees north, longitude in degrees east. Magnitude is ISC MS or mb otherwise. I0 – epicentral intensity (Scale MM). S – maximal isoseismal area with intensity II–III in thous. km2.
Highlights 1.
We analyzed the structural-tectonic setting, the parameters of the deep structure, the kinematic types of seismogenic structures and morphotectonics features of the present topography and the corresponding field tectonic stresses, determined on the basis of the decisions of the focal mechanisms of local earthquakes.
2. Create a model of modern geodynamics of the seismotectonic zones Chersky (the continental part of Arktika-Asian seismic belt)
3. We found that within the regional segments of the Central part of the seismotectonic zones Chersky (the Yana-Indigirka and Indigirka-Kolyma), in the context of transpression (compression, strike-slip faults), initiated by the interaction of the frontal structures of the areas of the contact pair of the Eurasian and North American lithospheric plates.
4. As a consequence a number of different terranes geodynamic nature are subjected to horizontal compression where the individual segments according to the system of conjugated multidirectional strike-slips faults.
5.
A number of terranes that form the basis of Chersky seismic zone , experience in recent horizontal compression, which forms a conjugated system reseparating ( left and right) strike-slip faults.