- Email: [email protected]
Deep seismic probing of continental crust and mantle
Tectonophysics 508 (2011) 1–5
Contents lists available at ScienceDirect
Tectonophysics j o u r n a l h o m e p a g e : w w w. e l s ev i e r. c o m / l o c a t e / t e c t o
Editorial
Deep seismic probing of continental crust and mantle
1. Introduction The first controlled source seismic experiment was carried out in Ireland about 150 years ago when Mallet (1852) measured the seismic velocity of the granites between two islands in the bay outside Dublin. This technological achievement led to a significant development of methods for observation of waves which have been refracted or reflected at wide-angle incidence in the sedimentary sequences or in the crystalline crust. It was followed by extensive development of the theory of seismic reflection and refraction by Knott (1899) and wave propagation by Lamb (1904). The need for locating enemy canons during World War I formed the background for substantial improvement of the understanding of seismic wave propagation and in-situ seismic velocity, which subsequently was continued by pioneering application to seismic prospecting. Mintrop took out the first patent for seismic refraction prospecting in the 1920s as an important method for determination of the location and size of salt domes and, thereby indirectly, shallow oil reservoirs in the bordering synclines. Ongoing development of controlled source reflection seismology was mainly driven by the need for identification of detailed structure. Therefore, application to imaging of structure of sedimentary basins was developed to a high level by the oil industry from the thirties and onwards. High resolution controlled-source methods based on observation of seismic refractions and wide-angle reflections were developed for both hydrocarbon exploration in sedimentary basins and for imaging of the crystalline crust. The first registrations of seismic normalincidence reflections from the crystalline crust and the Moho by use of chemical explosions as seismic source (Clowes et al., 1968; Meissner, 1967) were followed by rapid development of the deep seismic normal-incidence reflection methods for determination of structure in the Earth's crust. Controlled source seismological techniques were globally intensively used during the International Upper Mantle Project (UMP) from 1961 to 1970, when the experiments included the first experiments that aimed at imaging the mantle by refraction/wide-angle techniques. The following two major experiments should be mentioned: i. The Early Rise experiment was a collaborative project between US and Canadian institutions that covered most of North America (Warren et al., 1968). High resolution data was acquired at the standards of that time along 12 profiles radiating out from a common shot point in Lake Superior. Shots were repeatedly fired at the same location during night after daytime reinstallation of the seismographs. This major experiment still provides the best available controlled source seismic data from North America but, unfortunately, the profiles are non-reversed and the data is no longer available in digital format. The data has provided an invaluable resource for studies of lithospheric structure and the transition zone (Iyer et al., 1969; Lewis 0040-1951/$ – see front matter © 2010 Published by Elsevier B.V. doi:10.1016/j.tecto.2011.06.014
and Meyer, 1968; Masse, 1973; Thybo, 2006; Thybo et al., 2000; Thybo and Perchuc, 1997). Stimulated by these experiments, several seismic expeditions using offshore shots were also undertaken in Japan. The crustal section across Northeast Japan arc, which was characterised by a very low mantle velocity (7.5 km/s), was regarded as a typical structure model of an island arc (e.g.. Yoshii and Asano, 1972; Okada et al., 1979). 30 years later, the Deep Probe experiment provided a dataset at unprecedented resolution along a ca. 4000 km long profile at the western rim of the Rocky Mountains between central Canada and southern US (Gorman et al., 2002; Henstock et al., 1998). ii. The Soviet Peaceful Nuclear Explosion (PNE) programme between 1965 and 1988 is undoubtedly the largest controlled source seismological experiment ever carried out. The data was observed at dense arrays of seismographs to offsets of 4000 km for these compact sources in 500–1000 m deep boreholes, with high energy yield and precise location and onset time. This allows for reliable correlation of seismic phases with a well-defined, short source waveform. The programme included 41 nuclear detonations for geophysical studies (Sultanov et al., 1999). The sources were strong enough for recording of seismic energy on the global seismograph network. The data has been extensively interpreted for lithospheric structure (e.g. Mechie et al., 1993; Morozova et al., 2000; Nielsen et al., 1999, 2002; Thybo and Perchuc, 1997), and for seismic structure at the transition zone (Thybo et al., 2003a). Despite it was generally expected that the energy content would be too small at the high frequencies employed, the organisers of the programme decided to observe the time series for 1100 s after the shooting times, which corresponds to the traveltime from the surface to the centre of the Earth and back. Later studies have demonstrated that this decision by the organisers was justified when high-resolution images of the core mantle boundary were interpreted based on this data (Ross et al., 2004; Thybo et al., 2003b). Normal-incidence imaging of the mantle at high frequency has by now become a standard tool that was developed over the latest 20 years. Mantle reflectors down to depths of 240 km have been imaged by use of stacking techniques on multi-channel data sets. The advantage of this type of imaging is the very high resolution of the images, down to less than km scale at 200 km depth. Some examples include observation of reflections from close to the base of the lithosphere (Lie et al., 1990; MONA LISA Working Group, 1997; Steer et al., 1998). Also wide-angle techniques have recently been applied at unprecedented resolution for imaging of the upper mantle structure (Grad et al., 2002). The establishment of several national research groups that applied the normal-incidence techniques, including e.g. COCORP, BIRPS, DEKORP, ECORS, and LITHOPROBE, provided a stimulating environment for rapid development and refinement of the new methods for imaging the crustal structure with during the 70's and 80's (e.g. Bois
2
Editorial
and Damotte, 1983; Bortfeld, 1986; Brown et al., 1979; Clowes, 1984; Green et al., 1990; Klemperer and Hobbs, 1992; Matthews, 1982; Oliver et al., 1976). Some of the highlights from this period are spectacular images of significant structures in the crystalline crust which could be related to, in particular low angle, fault zones (e.g. Reston et al., 1996; Wernicke, 1981) and characteristic reflectivity from the lower crust (Klemperer, 1987; Levander et al., 1994; Meissner et al., 2006; Warner, 1990). The Moho was usually imaged by a direct reflection or inferred from the termination of reflectivity from the lower crust, although in some places it may not have been imaged by the normal-incidence reflection techniques (Cook et al., 1978; Eaton, 2006). Spectacular dipping reflections at the Moho and in the upper mantle provided images of structure from possible early Proterozoic or Archaean subduction or continental collision (Abramovitz et al., 1997; Abramovitz and Thybo, 2000; BABEL Working Group, 1989; Calvert et al., 1995). These findings provided important evidence for the timing of onset of plate tectonics. Also younger structures that may be related to active collision and subduction have been extensively determined (e.g. Abramovitz and Thybo, 2000; Ruiz et al., 2006; Warner et al., 1996). The seismic reflection profiling in Japan, which started in the 1990s, provided interesting crustal features of island arc including crustal delamination associated with arc–arc collision (e.g. Ito, 2002; Iwasaki et al., 2002; Tsumura et al., 1999) and inland active fault system created by backarc spreading and activated under the subsequent inversion tectonics (Sato et al., 2004). Recent development of the techniques has allowed high resolution imaging of structures at the continental margins which has demonstrated the high variability of types of passive margins (Mjelde et al., 2009; Reston et al., 1996; White et al., 2008), as well as at active margins (Iwasaki et al., 2002; Kato et al., 2004; Oncken et al., 1999; Yuan et al., 2000), continental rift zones (KRISP Working Party, 1991; Lyngsie et al., 2007; Mackenzie et al., 2005; Sandrin and Thybo, 2008; Thybo and Nielsen, 2009), and even active zones of continental collision (Behm et al., 2007; Bruckl et al., 2007; Kind et al., 2002; Makovsky et al., 1996; Nelson et al., 1996; Pfiffner et al., 1988). The geoscience community in Finland has recently been able to cover most of the country by high quality, highresolution seismic reflection profiles during the FIRE programme (Janik et al., 2009; Kukkonen and Lahtinen, 2006). Techniques are continuously being developed and their range of applicability expands with the availability of modern digital systems and large numbers of seismometers and hydrophones. This development has led to acquisition of data at extremely high resolution, which today allows researchers to obtain images of details of the structures created by dynamics in the Earth, such as fine scale structure of fault zones. 2. Symposium on Profiling of the Continents and their Margins The 13th International Symposium on Deep Seismic Profiling of the Continents and their Margins (Seismix, 2008) was held to make status of the development of techniques and to provide an overview of the significant new results that have been produced in recent years by the use of the techniques. The presentations were organised into the following 12 themes. • Passive continental margins • Continental mantle • Seismic exploration of mineral resources and seismic studies on nuclear waste disposal • Active continental margins and subduction structures • Seismic studies in polar regions • Integrated multidisciplinary case studies • Classical transects • Intracontinental collision and accretion • Continental rifts and basins • Innovative seismic acquisition and processing techniques
• Numerical modelling and inverse methods in seismology • Crust forming processes and seismic studies The presentations provided a dense coverage of these themes with many presentations devoted to studies of active plate boundaries with, in particular, many contributions on active continental margins including island arcs. Several presentations discussed multi-disciplinary studies and method development, which shows that the community is actively extending the applicability of the methods. The methodology has also become so well established that several presentations discussed “classical seismic transects” which also now have found outlet on the web-page of IGCP project no. 559 (http://www.earthscrust.org). The Seismix 2008 symposium was held on June 8–13 in Saariselkä in northernmost Finland. Similar to the previous symposia, all participants were accommodated at the same place, Hotel Riekonlinna in the oldest part of the Fennoscandian Shield. The mid-way excursion covered earlier gold exploration in northern Finland, and the post-symposium field excursion was organised to provide an overview of the geology of Lapland. There was a lively discussion forum both at the symposium and the excursion. The more than 100 delegates gave 66 oral and 97 poster presentations (Heikkinen et al., 2008). 3. This Volume This volume is based on presentations at the symposium and provides a status of seismic studies on the structure of the continental crust and lithosphere, including development of new techniques. It constitutes a natural continuation of the series of proceedings volumes from previous meetings (Barazangi and Brown, 1986a,b; Carbonell et al., 2000; Clowes and Green, 1994; Davey and Jones, 2004; Ito et al., 2009; Klemperer and Mooney, 1998a,b; Leven et al., 1990; Matthews and Smith, 1987; Meissner et al., 1991; Snyder et al., 2006; Thybo, 2002; White et al., 1996). A majority of the contributions discuss crustal structure of the interior and margins of the continents. These studies significantly extend the geological and geophysical knowledge of crustal structure and its implication for crustal formation and evolution. Very high resolution has been obtained in recent data acquisition. Lüschen et al. (this volume) present new detailed reflection seismic images of forearc structures in the subduction environment of the Sunda Arc. They document strong lateral variability along-strike of the subduction zone regarding the subducting oceanic plate, the interface between subducting and overriding plate, the accretionary wedge, the outer arc high and forearc basins. They interpret a wrench fault system in the eastern Lombok forearc basin that decouples the subduction regime of the Sunda Arc from the continent–island arc collision regime of the western Banda Arc. The observed tectonic activity of the entire forearc system reflects a high earthquake and tsunami hazard, similar to the western part of the Sunda Arc. Eccles et al. (this volume) present the results from traveltime tomography of compressional and converted shear wave arrivals along two North Atlantic continental margin profiles. In order to overcome the complexities introduced by magmatic intrusions, the authors use two different approaches for the tomographic inversion: One inversion with a flexible layer-based parameterisation which enables quality control of traveltime picks and investigation of the crustal structure; and another method with a regularised grid-based parameterisation, which requires correction of converted shear wave traveltimes to effective symmetric raypaths and allows the use of Monte Carlo analyses. The resulting velocity models indicate high lower-crustal velocities and sharp transitions in both velocity and Vp/Vs ratios across the continent–ocean transition. The velocities are consistent with established mixing trends between felsic continental crust and high magnesium mafic rock on both margins. The authors further show that converted shear wave data also provide constraints on the sub-basalt lithology on the Faroese margin.
Editorial
Fernández-Viejo et al. (this volume) present interpretations of the sedimentary strata in the continental margin of the eastern Bay of Biscay from the first reflection seismic survey in the area. They interpret three main sedimentary sequences related to various phases of the Alpine orogeny as also shown by compressional features in the sequences. The overall structure appears similar to active subduction prisms worldwide with along-strike variability. Buoyancy of the transitional crust and resistance to subduction is found to lead to strong plate coupling in the east, where oceanic crust is absent. Palomeras et al. (this volume) have carried out a multi-disciplinary study of features observed in the IBERSEIS deep reflection seismic profile in SW Iberia. By integrating seismic refraction and reflection data with topographic, geoid and gravity data they obtain improved constraints on parameters of crustal features and indication for the depth to the Lithosphere–Asthenosphere boundary. The crustal feature is interpreted to represent a body of high-density rocks with a high concentration of intruded mafic rocks. The interpretation of a new 100 km long crustal seismic reflection profile across central Sicily by Accaino et al. (this volume) provides images of spectacular deep seated thrusts and nappes, and an imbricate thrust system of rigid bodies. The authors developed a special acquisition geometry and processing sequence in order to obtain the high resolution images and for the first time image the Moho in the region. Zhang et al. (this volume) interpret extensional structures in the crust on the basis of new interpretation of a 320 km long seismic refraction profile in northern China. A thin, high-velocity crust–mantle transition zone may indicate that the bottom of the crust has been delaminated with coeval intrusion of melts from the mantle; also supported by low velocity of the lower crust. They infer a detachment in the middle crust, and find that lower-crustal flow and magma intrusion probably may lead to underestimation of the crustal-scale extensional factor representing the thinning of the lithosphere. Kanao et al. (this volume) present the interpretation of new refraction/wide-angle seismic data from eastern Dronning Maud's Land, Antarctica. It has required substantial effort to acquire the seismic data in this remote location in the framework of the SEAL programme (Structure and Evolution of the East Antarctic Lithosphere). By coherency enhancement processing they image laminated layering around the crust– mantle boundary. A repetitive crust–mantle transition zone is found to suggest the presence of compressional stress in a NE–SW orientation during the Pan-African. Successive break-up processes in midMesozoic could account for the formation of the stretched reflection structure above the Moho discontinuity. Pavlenkova (this volume) discusses the implications of the seismic structure for the rheology of the lithosphere. The analysis is based on data from the Soviet Peaceful Nuclear Explosion programme. She finds a series of interfaces in the lithospheric mantle, and that some of the layers should be regarded as brittle zones in the upper mantle. Xenoliths tend to originate from the depth interval of 100–200 km where Pavlenkova interprets high concentration of fluids which affect the mantle rheology substantially and may initiate partial melting. Pylypenko et al. (this volume) describe a new method for migration of wide-angle reflections and refractions and apply the method to data from the DOBRE profile across the Donbas foldbelt of the Dniepr– Donets palaeorift in Ukraine. The migration results enable the authors to identify hitherto unnoticed features of the crustal structure, including intra-crustal fault zones. The Moho is found to be a weak reflector in much of the profile, partly because it appears as a transition zone at the frequencies applied. Kumar et al. (this volume) have developed a new method for improving the signal to noise ratio in seismic data. The method makes use of a parsimonious representation of seismic data in the curvelet domain to perform the noise attenuation while preserving the coherent energy and its amplitude information. Curvelets facilitate signal to noise separation which can be subject to iterative inversion. The method is validated by application to both synthetic shot gathers and a synthetic stacked seismic section.
3
Curvelet denoising is also applied to deep crustal seismic reflection data where the signal-to-noise ratio is low, both to the pre-stack shot gathers and the post-stack data. Ground roll, random noise and much of the anomalous vertical energy is removed from the pre-stack shot gathers, to the extent that crustal reflections, including those from the Moho, are clearly seen on individual gathers. The authors find that curvelet denoising performs better than F-X deconvolution, and recommend this method as an important new tool for processing crustal seismic reflection data. Carpentier et al. (this volume) apply a statistical method for deriving stochastic parameters from seismic data to data from Abitibi–Grenville Province in Canada. The method maps lateral stochastic parameters, representing von Karman heterogeneity distributions in the crust, estimated from migrated deep reflection data. They find indication for significant spatial variations in macro-scale petrofabric within the tectonic terrains in depth as well as laterally, and they identify new features. They find that the data can be equally well interpreted in terms of collisional deformation and a major shear zone. Correlation length is found to be an especially robust parameter with moderate associated uncertainties. Acknowledgements The 13th International Symposium on Deep Seismic Profiling of the Continents and their Margins (Seismix, 2008) was organised in collaboration between the Institute of Seismology, the University of Helsinki and the Geological Survey of Finland. The meeting was sponsored by the International Geological Correlation Programme (IGCP), Project 474, the Federation of Finnish Learned Societies, the Finnish Academy of Science and Letters, and the Väisälä Foundation The editorial process of the present volume has benefited greatly from the involvement by the reviewers of the submitted manuscripts. We would like to acknowledge the significant contribution to the editorial process by the reviewers: Juan Carlos Afonso Irina M Artemieva Stephen Bannister Bettina Bayer Svetlana V. Bogdanova Larry D. Brown Ramon Carbonell Stefan Filip Anton Carpentier Piero Casero Ronald M. Clowes Frederick A. Cook David Eaton Alfons Eckstaller J. Gallart Karsten Gohl Bruce Ronald Goleby M. Grad Z. Hajnal Warren Hamilton A. Hirn Richard Hobbs Klaus Holliger John R. Hopper C.A. Hurich James Irving Joachim Jacobs Tomasz Janik Wilfried Jokat
4
Editorial
C. Juhlin N. Juhojuntti S. Klemperer Shuichi Kodaira Annakaisa Korja Elena Kozlovskaya Charlotte M. Krawczyk Yngve Kristoffersen Ilmo Kukkonen A. Levander Arto Luttinen Alireza Malehmir James Mechie John Nabelek Lars Nielsen Giuliano Francesco Panza T.C. Pharaoh Wolfgang Rabbel Kabir Roy-Chowdhury Tapio Ruotoistenmäki Hiroshi Sato David B Snyder R.A. Stephenson Manfred Stiller Isabelle Thinon Timo Tiira Jeroen van Hunen Olivier Vanderhaeghe Robert S. White H. Zeyen References Abramovitz, T., Thybo, H., 2000. Seismic images of Caledonian, lithosphere-scale collision structures in the southeastern North Sea along MONA LISA Profile 2. Tectonophysics 317, 27–54. Abramovitz, T., Berthelsen, A., Thybo, H., 1997. Proterozoic sutures and terranes in the southeastern Baltic Shield interpreted from BABEL deep seismic data. Tectonophysics 270, 259–277. BABEL Working Group, 1989. Seismic reflection evidence for the location of the Iapetus suture west of Ireland. J. Geol. Soc. Lond. 146, 409–412. Barazangi, M., Brown, L. (Eds.), 1986a. Reflection Seismology: A Global Perspective: Am. Geophys. Union. Geodyn. Ser., 13. 311 pp. Barazangi, M., Brown, L. (Eds.), 1986b. Reflection Seismology: The Continental Crust: Am. Geophys. Union, Geodyn. Ser., 14. 339 pp. Behm, M., Bruckl, E., Chwatal, W., Thybo, H., 2007. Application of stacking and inversion techniques to three-dimensional wide-angle reflection and refraction seismic data of the Eastern Alps. Geophys. J. Int. 170, 275–298. Bois, C., Damotte, B., 1983. Exploration of the Earth's crust — the ECORS program. Recherche 14, 850–853. Bortfeld, R.K., 1986. The German deep-reflection project Dekorp. Geophysics 51, 517–518. Brown, L., et al., 1979. Cocorp deep seismic-reflection studies of continental lithosphere — regional variations in intrabasement structure. Geophysics 44, 383–384. Bruckl, E., et al., 2007. Crustal structure due to collisional and escape tectonics in the Eastern Alps region based on profiles Alp01 and Alp02 from the ALP 2002 seismic experiment. J.Geophys. Res. 112 (B6) doi:10.1029/2006JB004687. Calvert, A.J., Sawyer, E.W., Davis, W.J., Ludden, J.N., 1995. Archean subduction inferred from seismic images of a mantle suture in the superior province. Nature 375 (6533), 670–674. Carbonell, R., Gallart, J., Torne, M., 2000. Deep seismic profiling of the continents and their margins — selected papers from the 8th International Symposium on Deep Seismic Profiling of the Continents and their Margins, Barcelona, Spain, 20–25 September 1998 — preface. Tectonophysics 329 (1–4), VII–VIII. Clowes, R.M., 1984. Phase-1 lithoprobe — a coordinated national geoscience project. Geosci. Can. 11 (3), 122–126. Clowes, R.M., Green, A.G., 1994. Seismic reflection probing of the continents and their margins. Tectonophysics 232, R7–R9. Clowes, R.M., Kanasewich, E., Cumming, G.L., 1968. Deep crustal seismic reflections at near-vertical incidence. Geophysics 33 (3), 441.
Cook, F.A., Brown, L.D., Kaufman, S., 1978. Nature of Moho on Cocorp reflection data. Trans. Am. Geophys. Union 59 (4), 389-389. Davey, F.J., Jones, L., 2004. Special issue — continental lithosphere — papers presented at the 10th International Symposium on Deep Seismic Profiling of the Continents and their Margins — Taupo, New Zealand, 6–10 January 2003 — introduction. Tectonophysics 388 (1–4), 1–5. Eaton, D.W., 2006. Multi-genetic origin of the continental Moho: insights from LITHOPROBE. Terra Nova 18 (1), 34–43. Gorman, A.R., et al., 2002. Deep probe: imaging the roots of western North America. Can. J. Earth Sci. 39 (3), 375–398. Grad, M., Keller, G.R., Thybo, H., Guterch, A., 2002. Lower lithospheric structure beneath the Trans-European Suture Zone from POLONAISE '97 seismic profiles. Tectonophysics 360 (1–4), 153–168. Green, A.G., et al., 1990. Deep-structure of an Archean greenstone terrane. Nature 344 (6264), 327–330. Heikkinen, Pekka; Kukkonen, Ilmo T.; Kuusisto, Minna; Heinonen, Suvi (eds.) 2008. SEISMIX 2008. The 13th International Symposium on Deep Seismic Profiling of the Continents and their Margins, June 8–13, 2008, Saariselkä, Inari, Finland: programme and abstracts. Institute of Seismology. University of Helsinki. Report S-48. Helsinki: Institute of Seismology. 102 pp. Henstock, T.J., Levander, A., Group D.P.W., 1998. Probing the Archean and Proterozoic lithosphere of western North America. GSA Today 8, 16–17. Ito, T., 2002. Active faulting, lower crustal lamination and ongoing Hidaka arc–arc collision, Hokkaido, Japan. In: Fujikawa, Y., Yoshida, A. (Eds.), Seismotectonics in Convergent Plate Boundary. TERRAPUB, Topyo, pp. 219–224. Ito, T., Iwasaki, T., Thybo, H., 2009. Deep seismic profiling of the continents and their margins — preface. Tectonophysics 472 (1–4), 1–5. Iwasaki, T., Yoshii, T., Ito, T., Sato, H., Hirata, N., 2002. Seismological features of island arc crust as inferred from recent seismic expeditions in Japan. Tectonophysics 355 (1–4), 53–66. Iyer, H.M., Pakiser, L.C., Stuart, D.J., Warren, D.H., 1969. Project Early Rise; seismic probing of the upper mantle. J. Geophys. Res. 74 (17), 4409–4441. Janik, T., Kozlovskaya, E., Heikkinen, P., Yliniemi, J., Silvennoinen, H., 2009. Evidence for preservation of crustal root beneath the Proterozoic Lapland-Kola orogen (northern Fennoscandian shield) derived from P and S wave velocity models of POLAR and HUKKA wide-angle reflection and refraction profiles and FIRE4 reflection transect. J. Geophys. Res. 114 doi:10.1029/2008JB005689. Kato, N., et al., 2004. Has the plate boundary shifted from central Hokkaido to the eastern part of the Sea of Japan? Tectonophysics 388 (1–4), 75–84. Kind, R., et al., 2002. Seismic images of crust and upper mantle beneath Tibet: evidence for Eurasian plate subduction. Science 298 (5596), 1219–1221. Klemperer, S.L., 1987. A relation between continental heat flow and the seismic reflectivity of the lower crust. J. Geophys. 61 (1), 1–11. Klemperer, S.L., Hobbs, R.W., 1992. The BIRPS Atlas: Deep Seismic Reflection Profiles Around the British Isles. Cambridge University press. 128 pp. and 100 seismic sections. Klemperer, S.L., Mooney, W.D. (Eds.), 1998a. Special Issue — Deep Seismic Profiling of the Continents, I: General Results and New Methods: Tectonophysics, 286, pp. IX–XIV. Klemperer, S.L., Mooney, W.D. (Eds.), 1998b. Deep Seismic Profiling of the Continents, II: A Global Survey: Tectonophysics, 288, pp. VII–VIII. Knott, C.G., 1899. Reflexion and refraction of elastic waves wth seismological applications. Philos Mag. 48, 64–97. KRISP Working Party, 1991. Large-scale variation in lithospheric structure along and across the Kenya rift. Nature 354 (6350), 223–227. Kukkonen, I.T., Lahtinen, R., 2006. Finnish Reflection Experiment FIRE 2001–2005. Geological Survey of Finland: Special Paper, Espoo. 247 ppp. + 15 app. + CD-ROM pp. Lamb, H., 1904. On the propagation of tremors over the surface of an elastic solid. Philos. Trans. R. Soc. Lond. A203, 1–42. Levander, A., et al., 1994. The crust as a heterogeneous “optical” medium, or “crocodiles in the mist”. Tectonophysics 232, 281–297. Leven, J.H., Finlaysson, D.M., Wright, C., Dooley, J.C., Kennett, B.L.N. (Eds.), 1990. Seismic Probing of Continents and their Margins: Tectonophysics, 173. Lewis, B.T., Meyer, R.P., 1968. A seismic investigation of the upper mantle to the west of Lake Superior. Bull. Seis. Soc. Am. 58 (2), 565–596. Lie, J.E., Pedersen, T., Husebye, E.S., 1990. Observations of seismic reflectors in the lower lithosphere beneath the Skagerrak. Nature 346 (6280), 165–168. Lyngsie, S.B., Thybo, H., Lang, R., 2007. Rifting and lower crustal reflectivity: a case study of the intracratonic Dniepr–Donets rift zone, Ukraine. J. Geophys. Res. 112, B12402 doi:10.1029/2006JB004795. Mackenzie, G.D., Thybo, H., Maguire, P.K.H., 2005. Crustal velocity structure across the Main Ethiopian Rift: results from two-dimensional wide-angle seismic modelling. Geophys. J. Int. 162 (3), 994–1006. Makovsky, Y., et al., 1996. INDEPTH wide-angle reflection observation of P-wave-to-Swave conversion from crustal bright spots in Tibet. Science 274 (5293), 1690–1691. Mallet, R., 1852. Second report on the facts of earthquake phenomena. Report of the Twenty-first Meeting of the British Association for the Advancement of Science, pp. 272–320. Masse, R.P., 1973. Compressional velocity distribution beneath central and eastern North America. Bull. Seis. Soc. Am. 63 (3), 911–935. Matthews, D.H., 1982. Birps — deep seismic-reflection profiling around the British-Isles. Nature 298 (5876), 709–710. Matthews, D.H., Smith, C. (Eds.), 1987. Deep Seismic Reflection Profiling of the Continental Lithosphere: Geophys. J.R. Astron. Soc., 89. 447 pp. Mechie, J., et al., 1993. P-wave Mantle Velocity Structure beneath Northern Eurasia from Long-range Recordings along the Profile Quartz. : Structure and Evolution of the European Lithosphere and Upper Mantle; 7th Conference of the European Union of Geosciences, 79. 1–2, pp. 269–286.
Editorial Meissner, R., 1967. Exploring deep interfaces by seismic wide angle measurements. Geophys. Prospect. 15, 598–617. Meissner, R., et al. (Ed.), 1991. Continental Lithosphere: Deep Seismic Reflections: Am. Geophys. Union, Geodyn. Ser., 22. 450 pp. Meissner, R., Rabbel, W., Kern, H., 2006. Seismic lamination and anisotropy of the lower continental crust. Tectonophysics 416 (1–4), 81–99. Mjelde, R., Faleide, J.I., Breivik, A.J., Rauma, T., 2009. Lower crustal composition and crustal lineaments on the Vøring Margin, NE Atlantic: a review. Tectonophysics 472 (14), 183–193. MONA LISA Working Group, 1997. MONA LISA; deep seismic investigations of the lithosphere in the southeastern North Sea. Tectonophysics 269 (1–2), 1–19. Morozova, E.A., Morozov, I.B., Smithson, S.B., Solodilov, L., 2000. Lithospheric boundaries and upper mantle heterogeneity beneath Russian Eurasia: evidence from the DSS profile QUARTZ. Tectonophysics 329 (1–4), 333–344. Nelson, K.D., et al., 1996. Partially molten middle crust beneath southern Tibet; synthesis of Project INDEPTH results. Science 274 (5293), 1684–1688. Nielsen, L., Thybo, H., Solodilov, L., 1999. Seismic tomographic inversion of Russian PNE data along profile Kraton. Geophys. Res. Lett. 26 (22), 3413–3416. Nielsen, L., Thybo, H., Egorkin, A.V., 2002. Implications of seismic scattering below the 8 degrees discontinuity along PNE profile Kraton. Tectonophysics 358 (1–4), 135–150. Okada, H., et al., 1979. Regionality of the upper mantle around northern Japan, as revealed by big explosion at sea: I. SEIHA-I explosion experiment. J. Phys, Earth 27, S15–S32 suppl.. Oliver, J.E., Dobrin, M., Kaufman, S., Meyer, R., Phinney, R., 1976. Continuous seismic reflection profiling of the deep basement, Hardeman County, Texas. Geol. Soc. Am. Bull. 87, 1537–1546. Oncken, O., et al., 1999. Seismic reflection image revealing offset of Andean subductionzone earthquake locations into oceanic mantle. Nature 397 (6717), 341–344. Pfiffner, O.A., Frei, W., Finckh, P., Valasek, P., 1988. Deep seismic reflection profiling in the Swiss Alps; explosion seismology results for line NFP 20-EAST. Geology 16 (11), 987–990. Reston, T.J., Krawczyk, C.M., Klaeschen, D., 1996. The S reflector west of Galicia (Spain); evidence from prestack depth migration for detachment faulting during continental breakup. J. Geophys. Res. 101 (4), 8075–8091. Ross, A.R., Thybo, H., Solidilov, L.N., 2004. Reflection seismic profiles of the core–mantle boundary. J. Geophys. Res. 109 (B8) doi:10.1029/2003JB002515. Ruiz, M., et al., 2006. Seismic activity at the western Pyrenean edge. Tectonophysics 412 (3–4), 217–235. Sandrin, A., Thybo, H., 2008. Seismic constraints on a large mafic intrusion with implications for the subsidence history of the Danish Basin. J. Geophys. Res. 113 (B9) doi:10.1029/2007JB005067. Sato, H., et al., 2004. Formation and shortening deformation of a back-arc rift basin revealed by deep seismic profiling. Tectonophysics 388, 47–58. Snyder, D.B., Eaton, D.W., Hurich, C.A., 2006. Special issue — seismic probing of continents and their margins — introduction. Tectonophysics 420 (1–2), 1–4. Steer, D.N., Knapp, J.H., Brown, L.D., 1998. Super-deep reflection profiling: exploring the continental mantle lid. Tectonophysics 286 (1–4), 111–121. Sultanov, D.D., Murphy, J.R., Rubinstein, K.D., 1999. A seismic source summary for Soviet peaceful nuclear explosions. Bull. Seis. Soc. Am. 89 (3), 640–647. Thybo, H., 2002. Deep seismic probing of the continents and their margins — selected papers from the 9th biennial meeting held in Ulvik, Norway. Tectonophysics 355 (1–4), 1–5. Thybo, H., 2006. The heterogeneous upper mantle low velocity zone. Tectonophysics 416 (1–4), 53–79.
5
Thybo, H., Nielsen, C.A., 2009. Magma-compensated crustal thinning in continental rift zones. Nature 457, 873–876 doi:10.1038/nature07688. Thybo, H., Perchuc, E., 1997. The seismic 8 degrees discontinuity and partial melting in continental mantle. Science 275 (5306), 1626–1629. Thybo, H., Perchuc, E., Zhou, S., 2000. Intraplate earthquakes and a seismically defined lateral transition in the upper mantle. Geophys. Res. Lett. 27 (23), 3953–3956. Thybo, H., Nielsen, L., Perchuc, E., 2003a. Seismic scattering at the top of the mantle Transition Zone. Earth Plan. Sci. Lett. 216 (3), 259–269. Thybo, H., Ross, A.R., Egorkin, A.V., 2003b. Explosion seismic reflections from the Earth's core. Earth Plan. Sci. Lett. 216 (4), 693–702. Tsumura, N., et al., 1999. Delamination-wedge structure beneath the Hidaka collision zone, central Hokkaido, Japan inferred from seismic reflection profiling. Geophys. Res. Lett. 26, 1057–1060. Warner, M.R., 1990. Basalts, water, or shear zones in the lower continental crust? Tectonophysics 173 (1–4), 163–174. Warner, M., et al., 1996. Seismic reflections from the mantle represent relict subduction zones within the continental lithosphere. Geology 24 (1), 39–42. Warren, D.H., et al., 1968. Project Early Rise travel times and amplitudes. U.S. Geol. Surv., Open-File Rep., Menlo Park. 150 pp. Wernicke, B., 1981. Low-angle normal faults in the Basin and Range Province; nappe tectonics in an extending orogen. Nature 291 (5817), 645–648. White, D.J., Ansorge, J., Bodoky, T.J., Hajnal, Z., 1996. Special issue — seismic reflection probing of the continents and their margins — preface. Tectonophysics 264, R7–R9. White, R.S., Smith, L.K., Roberts, A.W., Christie, P.A.F., Kusznir, N.J., 2008. Lower-crustal intrusion on the North Atlantic continental margin. Nature 452 (7186), 460-U6. Yoshii, T., Asano, S., 1972. Time-term analysis of explosion seismic data. J. Phys. Earth. 20, 47–57. Yuan, X., et al., 2000. Subduction and collision processes in the Central Andes constrained by converted seismic phases. Nature 408 (6815), 958–961.
H. Thybo⁎ Department of Geography and Geology, University of Copenhagen, Øster Voldgade 10, DK-1350 Copenhagen K, Denmark ⁎Corresponding author. E-mail address: [email protected]. P. Heikkinen Institute of Seismology, PL 68, Gustaf Hällströmin katu 2b, FI-00014 University of Helsinki, Finland I. Kukkonen Geological Survey of Finland (GTK), Betonimiehenkuja 4, FI-02150, Espoo, Finland 28 September 2010
Contents lists available at ScienceDirect
Tectonophysics j o u r n a l h o m e p a g e : w w w. e l s ev i e r. c o m / l o c a t e / t e c t o
Editorial
Deep seismic probing of continental crust and mantle
1. Introduction The first controlled source seismic experiment was carried out in Ireland about 150 years ago when Mallet (1852) measured the seismic velocity of the granites between two islands in the bay outside Dublin. This technological achievement led to a significant development of methods for observation of waves which have been refracted or reflected at wide-angle incidence in the sedimentary sequences or in the crystalline crust. It was followed by extensive development of the theory of seismic reflection and refraction by Knott (1899) and wave propagation by Lamb (1904). The need for locating enemy canons during World War I formed the background for substantial improvement of the understanding of seismic wave propagation and in-situ seismic velocity, which subsequently was continued by pioneering application to seismic prospecting. Mintrop took out the first patent for seismic refraction prospecting in the 1920s as an important method for determination of the location and size of salt domes and, thereby indirectly, shallow oil reservoirs in the bordering synclines. Ongoing development of controlled source reflection seismology was mainly driven by the need for identification of detailed structure. Therefore, application to imaging of structure of sedimentary basins was developed to a high level by the oil industry from the thirties and onwards. High resolution controlled-source methods based on observation of seismic refractions and wide-angle reflections were developed for both hydrocarbon exploration in sedimentary basins and for imaging of the crystalline crust. The first registrations of seismic normalincidence reflections from the crystalline crust and the Moho by use of chemical explosions as seismic source (Clowes et al., 1968; Meissner, 1967) were followed by rapid development of the deep seismic normal-incidence reflection methods for determination of structure in the Earth's crust. Controlled source seismological techniques were globally intensively used during the International Upper Mantle Project (UMP) from 1961 to 1970, when the experiments included the first experiments that aimed at imaging the mantle by refraction/wide-angle techniques. The following two major experiments should be mentioned: i. The Early Rise experiment was a collaborative project between US and Canadian institutions that covered most of North America (Warren et al., 1968). High resolution data was acquired at the standards of that time along 12 profiles radiating out from a common shot point in Lake Superior. Shots were repeatedly fired at the same location during night after daytime reinstallation of the seismographs. This major experiment still provides the best available controlled source seismic data from North America but, unfortunately, the profiles are non-reversed and the data is no longer available in digital format. The data has provided an invaluable resource for studies of lithospheric structure and the transition zone (Iyer et al., 1969; Lewis 0040-1951/$ – see front matter © 2010 Published by Elsevier B.V. doi:10.1016/j.tecto.2011.06.014
and Meyer, 1968; Masse, 1973; Thybo, 2006; Thybo et al., 2000; Thybo and Perchuc, 1997). Stimulated by these experiments, several seismic expeditions using offshore shots were also undertaken in Japan. The crustal section across Northeast Japan arc, which was characterised by a very low mantle velocity (7.5 km/s), was regarded as a typical structure model of an island arc (e.g.. Yoshii and Asano, 1972; Okada et al., 1979). 30 years later, the Deep Probe experiment provided a dataset at unprecedented resolution along a ca. 4000 km long profile at the western rim of the Rocky Mountains between central Canada and southern US (Gorman et al., 2002; Henstock et al., 1998). ii. The Soviet Peaceful Nuclear Explosion (PNE) programme between 1965 and 1988 is undoubtedly the largest controlled source seismological experiment ever carried out. The data was observed at dense arrays of seismographs to offsets of 4000 km for these compact sources in 500–1000 m deep boreholes, with high energy yield and precise location and onset time. This allows for reliable correlation of seismic phases with a well-defined, short source waveform. The programme included 41 nuclear detonations for geophysical studies (Sultanov et al., 1999). The sources were strong enough for recording of seismic energy on the global seismograph network. The data has been extensively interpreted for lithospheric structure (e.g. Mechie et al., 1993; Morozova et al., 2000; Nielsen et al., 1999, 2002; Thybo and Perchuc, 1997), and for seismic structure at the transition zone (Thybo et al., 2003a). Despite it was generally expected that the energy content would be too small at the high frequencies employed, the organisers of the programme decided to observe the time series for 1100 s after the shooting times, which corresponds to the traveltime from the surface to the centre of the Earth and back. Later studies have demonstrated that this decision by the organisers was justified when high-resolution images of the core mantle boundary were interpreted based on this data (Ross et al., 2004; Thybo et al., 2003b). Normal-incidence imaging of the mantle at high frequency has by now become a standard tool that was developed over the latest 20 years. Mantle reflectors down to depths of 240 km have been imaged by use of stacking techniques on multi-channel data sets. The advantage of this type of imaging is the very high resolution of the images, down to less than km scale at 200 km depth. Some examples include observation of reflections from close to the base of the lithosphere (Lie et al., 1990; MONA LISA Working Group, 1997; Steer et al., 1998). Also wide-angle techniques have recently been applied at unprecedented resolution for imaging of the upper mantle structure (Grad et al., 2002). The establishment of several national research groups that applied the normal-incidence techniques, including e.g. COCORP, BIRPS, DEKORP, ECORS, and LITHOPROBE, provided a stimulating environment for rapid development and refinement of the new methods for imaging the crustal structure with during the 70's and 80's (e.g. Bois
2
Editorial
and Damotte, 1983; Bortfeld, 1986; Brown et al., 1979; Clowes, 1984; Green et al., 1990; Klemperer and Hobbs, 1992; Matthews, 1982; Oliver et al., 1976). Some of the highlights from this period are spectacular images of significant structures in the crystalline crust which could be related to, in particular low angle, fault zones (e.g. Reston et al., 1996; Wernicke, 1981) and characteristic reflectivity from the lower crust (Klemperer, 1987; Levander et al., 1994; Meissner et al., 2006; Warner, 1990). The Moho was usually imaged by a direct reflection or inferred from the termination of reflectivity from the lower crust, although in some places it may not have been imaged by the normal-incidence reflection techniques (Cook et al., 1978; Eaton, 2006). Spectacular dipping reflections at the Moho and in the upper mantle provided images of structure from possible early Proterozoic or Archaean subduction or continental collision (Abramovitz et al., 1997; Abramovitz and Thybo, 2000; BABEL Working Group, 1989; Calvert et al., 1995). These findings provided important evidence for the timing of onset of plate tectonics. Also younger structures that may be related to active collision and subduction have been extensively determined (e.g. Abramovitz and Thybo, 2000; Ruiz et al., 2006; Warner et al., 1996). The seismic reflection profiling in Japan, which started in the 1990s, provided interesting crustal features of island arc including crustal delamination associated with arc–arc collision (e.g. Ito, 2002; Iwasaki et al., 2002; Tsumura et al., 1999) and inland active fault system created by backarc spreading and activated under the subsequent inversion tectonics (Sato et al., 2004). Recent development of the techniques has allowed high resolution imaging of structures at the continental margins which has demonstrated the high variability of types of passive margins (Mjelde et al., 2009; Reston et al., 1996; White et al., 2008), as well as at active margins (Iwasaki et al., 2002; Kato et al., 2004; Oncken et al., 1999; Yuan et al., 2000), continental rift zones (KRISP Working Party, 1991; Lyngsie et al., 2007; Mackenzie et al., 2005; Sandrin and Thybo, 2008; Thybo and Nielsen, 2009), and even active zones of continental collision (Behm et al., 2007; Bruckl et al., 2007; Kind et al., 2002; Makovsky et al., 1996; Nelson et al., 1996; Pfiffner et al., 1988). The geoscience community in Finland has recently been able to cover most of the country by high quality, highresolution seismic reflection profiles during the FIRE programme (Janik et al., 2009; Kukkonen and Lahtinen, 2006). Techniques are continuously being developed and their range of applicability expands with the availability of modern digital systems and large numbers of seismometers and hydrophones. This development has led to acquisition of data at extremely high resolution, which today allows researchers to obtain images of details of the structures created by dynamics in the Earth, such as fine scale structure of fault zones. 2. Symposium on Profiling of the Continents and their Margins The 13th International Symposium on Deep Seismic Profiling of the Continents and their Margins (Seismix, 2008) was held to make status of the development of techniques and to provide an overview of the significant new results that have been produced in recent years by the use of the techniques. The presentations were organised into the following 12 themes. • Passive continental margins • Continental mantle • Seismic exploration of mineral resources and seismic studies on nuclear waste disposal • Active continental margins and subduction structures • Seismic studies in polar regions • Integrated multidisciplinary case studies • Classical transects • Intracontinental collision and accretion • Continental rifts and basins • Innovative seismic acquisition and processing techniques
• Numerical modelling and inverse methods in seismology • Crust forming processes and seismic studies The presentations provided a dense coverage of these themes with many presentations devoted to studies of active plate boundaries with, in particular, many contributions on active continental margins including island arcs. Several presentations discussed multi-disciplinary studies and method development, which shows that the community is actively extending the applicability of the methods. The methodology has also become so well established that several presentations discussed “classical seismic transects” which also now have found outlet on the web-page of IGCP project no. 559 (http://www.earthscrust.org). The Seismix 2008 symposium was held on June 8–13 in Saariselkä in northernmost Finland. Similar to the previous symposia, all participants were accommodated at the same place, Hotel Riekonlinna in the oldest part of the Fennoscandian Shield. The mid-way excursion covered earlier gold exploration in northern Finland, and the post-symposium field excursion was organised to provide an overview of the geology of Lapland. There was a lively discussion forum both at the symposium and the excursion. The more than 100 delegates gave 66 oral and 97 poster presentations (Heikkinen et al., 2008). 3. This Volume This volume is based on presentations at the symposium and provides a status of seismic studies on the structure of the continental crust and lithosphere, including development of new techniques. It constitutes a natural continuation of the series of proceedings volumes from previous meetings (Barazangi and Brown, 1986a,b; Carbonell et al., 2000; Clowes and Green, 1994; Davey and Jones, 2004; Ito et al., 2009; Klemperer and Mooney, 1998a,b; Leven et al., 1990; Matthews and Smith, 1987; Meissner et al., 1991; Snyder et al., 2006; Thybo, 2002; White et al., 1996). A majority of the contributions discuss crustal structure of the interior and margins of the continents. These studies significantly extend the geological and geophysical knowledge of crustal structure and its implication for crustal formation and evolution. Very high resolution has been obtained in recent data acquisition. Lüschen et al. (this volume) present new detailed reflection seismic images of forearc structures in the subduction environment of the Sunda Arc. They document strong lateral variability along-strike of the subduction zone regarding the subducting oceanic plate, the interface between subducting and overriding plate, the accretionary wedge, the outer arc high and forearc basins. They interpret a wrench fault system in the eastern Lombok forearc basin that decouples the subduction regime of the Sunda Arc from the continent–island arc collision regime of the western Banda Arc. The observed tectonic activity of the entire forearc system reflects a high earthquake and tsunami hazard, similar to the western part of the Sunda Arc. Eccles et al. (this volume) present the results from traveltime tomography of compressional and converted shear wave arrivals along two North Atlantic continental margin profiles. In order to overcome the complexities introduced by magmatic intrusions, the authors use two different approaches for the tomographic inversion: One inversion with a flexible layer-based parameterisation which enables quality control of traveltime picks and investigation of the crustal structure; and another method with a regularised grid-based parameterisation, which requires correction of converted shear wave traveltimes to effective symmetric raypaths and allows the use of Monte Carlo analyses. The resulting velocity models indicate high lower-crustal velocities and sharp transitions in both velocity and Vp/Vs ratios across the continent–ocean transition. The velocities are consistent with established mixing trends between felsic continental crust and high magnesium mafic rock on both margins. The authors further show that converted shear wave data also provide constraints on the sub-basalt lithology on the Faroese margin.
Editorial
Fernández-Viejo et al. (this volume) present interpretations of the sedimentary strata in the continental margin of the eastern Bay of Biscay from the first reflection seismic survey in the area. They interpret three main sedimentary sequences related to various phases of the Alpine orogeny as also shown by compressional features in the sequences. The overall structure appears similar to active subduction prisms worldwide with along-strike variability. Buoyancy of the transitional crust and resistance to subduction is found to lead to strong plate coupling in the east, where oceanic crust is absent. Palomeras et al. (this volume) have carried out a multi-disciplinary study of features observed in the IBERSEIS deep reflection seismic profile in SW Iberia. By integrating seismic refraction and reflection data with topographic, geoid and gravity data they obtain improved constraints on parameters of crustal features and indication for the depth to the Lithosphere–Asthenosphere boundary. The crustal feature is interpreted to represent a body of high-density rocks with a high concentration of intruded mafic rocks. The interpretation of a new 100 km long crustal seismic reflection profile across central Sicily by Accaino et al. (this volume) provides images of spectacular deep seated thrusts and nappes, and an imbricate thrust system of rigid bodies. The authors developed a special acquisition geometry and processing sequence in order to obtain the high resolution images and for the first time image the Moho in the region. Zhang et al. (this volume) interpret extensional structures in the crust on the basis of new interpretation of a 320 km long seismic refraction profile in northern China. A thin, high-velocity crust–mantle transition zone may indicate that the bottom of the crust has been delaminated with coeval intrusion of melts from the mantle; also supported by low velocity of the lower crust. They infer a detachment in the middle crust, and find that lower-crustal flow and magma intrusion probably may lead to underestimation of the crustal-scale extensional factor representing the thinning of the lithosphere. Kanao et al. (this volume) present the interpretation of new refraction/wide-angle seismic data from eastern Dronning Maud's Land, Antarctica. It has required substantial effort to acquire the seismic data in this remote location in the framework of the SEAL programme (Structure and Evolution of the East Antarctic Lithosphere). By coherency enhancement processing they image laminated layering around the crust– mantle boundary. A repetitive crust–mantle transition zone is found to suggest the presence of compressional stress in a NE–SW orientation during the Pan-African. Successive break-up processes in midMesozoic could account for the formation of the stretched reflection structure above the Moho discontinuity. Pavlenkova (this volume) discusses the implications of the seismic structure for the rheology of the lithosphere. The analysis is based on data from the Soviet Peaceful Nuclear Explosion programme. She finds a series of interfaces in the lithospheric mantle, and that some of the layers should be regarded as brittle zones in the upper mantle. Xenoliths tend to originate from the depth interval of 100–200 km where Pavlenkova interprets high concentration of fluids which affect the mantle rheology substantially and may initiate partial melting. Pylypenko et al. (this volume) describe a new method for migration of wide-angle reflections and refractions and apply the method to data from the DOBRE profile across the Donbas foldbelt of the Dniepr– Donets palaeorift in Ukraine. The migration results enable the authors to identify hitherto unnoticed features of the crustal structure, including intra-crustal fault zones. The Moho is found to be a weak reflector in much of the profile, partly because it appears as a transition zone at the frequencies applied. Kumar et al. (this volume) have developed a new method for improving the signal to noise ratio in seismic data. The method makes use of a parsimonious representation of seismic data in the curvelet domain to perform the noise attenuation while preserving the coherent energy and its amplitude information. Curvelets facilitate signal to noise separation which can be subject to iterative inversion. The method is validated by application to both synthetic shot gathers and a synthetic stacked seismic section.
3
Curvelet denoising is also applied to deep crustal seismic reflection data where the signal-to-noise ratio is low, both to the pre-stack shot gathers and the post-stack data. Ground roll, random noise and much of the anomalous vertical energy is removed from the pre-stack shot gathers, to the extent that crustal reflections, including those from the Moho, are clearly seen on individual gathers. The authors find that curvelet denoising performs better than F-X deconvolution, and recommend this method as an important new tool for processing crustal seismic reflection data. Carpentier et al. (this volume) apply a statistical method for deriving stochastic parameters from seismic data to data from Abitibi–Grenville Province in Canada. The method maps lateral stochastic parameters, representing von Karman heterogeneity distributions in the crust, estimated from migrated deep reflection data. They find indication for significant spatial variations in macro-scale petrofabric within the tectonic terrains in depth as well as laterally, and they identify new features. They find that the data can be equally well interpreted in terms of collisional deformation and a major shear zone. Correlation length is found to be an especially robust parameter with moderate associated uncertainties. Acknowledgements The 13th International Symposium on Deep Seismic Profiling of the Continents and their Margins (Seismix, 2008) was organised in collaboration between the Institute of Seismology, the University of Helsinki and the Geological Survey of Finland. The meeting was sponsored by the International Geological Correlation Programme (IGCP), Project 474, the Federation of Finnish Learned Societies, the Finnish Academy of Science and Letters, and the Väisälä Foundation The editorial process of the present volume has benefited greatly from the involvement by the reviewers of the submitted manuscripts. We would like to acknowledge the significant contribution to the editorial process by the reviewers: Juan Carlos Afonso Irina M Artemieva Stephen Bannister Bettina Bayer Svetlana V. Bogdanova Larry D. Brown Ramon Carbonell Stefan Filip Anton Carpentier Piero Casero Ronald M. Clowes Frederick A. Cook David Eaton Alfons Eckstaller J. Gallart Karsten Gohl Bruce Ronald Goleby M. Grad Z. Hajnal Warren Hamilton A. Hirn Richard Hobbs Klaus Holliger John R. Hopper C.A. Hurich James Irving Joachim Jacobs Tomasz Janik Wilfried Jokat
4
Editorial
C. Juhlin N. Juhojuntti S. Klemperer Shuichi Kodaira Annakaisa Korja Elena Kozlovskaya Charlotte M. Krawczyk Yngve Kristoffersen Ilmo Kukkonen A. Levander Arto Luttinen Alireza Malehmir James Mechie John Nabelek Lars Nielsen Giuliano Francesco Panza T.C. Pharaoh Wolfgang Rabbel Kabir Roy-Chowdhury Tapio Ruotoistenmäki Hiroshi Sato David B Snyder R.A. Stephenson Manfred Stiller Isabelle Thinon Timo Tiira Jeroen van Hunen Olivier Vanderhaeghe Robert S. White H. Zeyen References Abramovitz, T., Thybo, H., 2000. Seismic images of Caledonian, lithosphere-scale collision structures in the southeastern North Sea along MONA LISA Profile 2. Tectonophysics 317, 27–54. Abramovitz, T., Berthelsen, A., Thybo, H., 1997. Proterozoic sutures and terranes in the southeastern Baltic Shield interpreted from BABEL deep seismic data. Tectonophysics 270, 259–277. BABEL Working Group, 1989. Seismic reflection evidence for the location of the Iapetus suture west of Ireland. J. Geol. Soc. Lond. 146, 409–412. Barazangi, M., Brown, L. (Eds.), 1986a. Reflection Seismology: A Global Perspective: Am. Geophys. Union. Geodyn. Ser., 13. 311 pp. Barazangi, M., Brown, L. (Eds.), 1986b. Reflection Seismology: The Continental Crust: Am. Geophys. Union, Geodyn. Ser., 14. 339 pp. Behm, M., Bruckl, E., Chwatal, W., Thybo, H., 2007. Application of stacking and inversion techniques to three-dimensional wide-angle reflection and refraction seismic data of the Eastern Alps. Geophys. J. Int. 170, 275–298. Bois, C., Damotte, B., 1983. Exploration of the Earth's crust — the ECORS program. Recherche 14, 850–853. Bortfeld, R.K., 1986. The German deep-reflection project Dekorp. Geophysics 51, 517–518. Brown, L., et al., 1979. Cocorp deep seismic-reflection studies of continental lithosphere — regional variations in intrabasement structure. Geophysics 44, 383–384. Bruckl, E., et al., 2007. Crustal structure due to collisional and escape tectonics in the Eastern Alps region based on profiles Alp01 and Alp02 from the ALP 2002 seismic experiment. J.Geophys. Res. 112 (B6) doi:10.1029/2006JB004687. Calvert, A.J., Sawyer, E.W., Davis, W.J., Ludden, J.N., 1995. Archean subduction inferred from seismic images of a mantle suture in the superior province. Nature 375 (6533), 670–674. Carbonell, R., Gallart, J., Torne, M., 2000. Deep seismic profiling of the continents and their margins — selected papers from the 8th International Symposium on Deep Seismic Profiling of the Continents and their Margins, Barcelona, Spain, 20–25 September 1998 — preface. Tectonophysics 329 (1–4), VII–VIII. Clowes, R.M., 1984. Phase-1 lithoprobe — a coordinated national geoscience project. Geosci. Can. 11 (3), 122–126. Clowes, R.M., Green, A.G., 1994. Seismic reflection probing of the continents and their margins. Tectonophysics 232, R7–R9. Clowes, R.M., Kanasewich, E., Cumming, G.L., 1968. Deep crustal seismic reflections at near-vertical incidence. Geophysics 33 (3), 441.
Cook, F.A., Brown, L.D., Kaufman, S., 1978. Nature of Moho on Cocorp reflection data. Trans. Am. Geophys. Union 59 (4), 389-389. Davey, F.J., Jones, L., 2004. Special issue — continental lithosphere — papers presented at the 10th International Symposium on Deep Seismic Profiling of the Continents and their Margins — Taupo, New Zealand, 6–10 January 2003 — introduction. Tectonophysics 388 (1–4), 1–5. Eaton, D.W., 2006. Multi-genetic origin of the continental Moho: insights from LITHOPROBE. Terra Nova 18 (1), 34–43. Gorman, A.R., et al., 2002. Deep probe: imaging the roots of western North America. Can. J. Earth Sci. 39 (3), 375–398. Grad, M., Keller, G.R., Thybo, H., Guterch, A., 2002. Lower lithospheric structure beneath the Trans-European Suture Zone from POLONAISE '97 seismic profiles. Tectonophysics 360 (1–4), 153–168. Green, A.G., et al., 1990. Deep-structure of an Archean greenstone terrane. Nature 344 (6264), 327–330. Heikkinen, Pekka; Kukkonen, Ilmo T.; Kuusisto, Minna; Heinonen, Suvi (eds.) 2008. SEISMIX 2008. The 13th International Symposium on Deep Seismic Profiling of the Continents and their Margins, June 8–13, 2008, Saariselkä, Inari, Finland: programme and abstracts. Institute of Seismology. University of Helsinki. Report S-48. Helsinki: Institute of Seismology. 102 pp. Henstock, T.J., Levander, A., Group D.P.W., 1998. Probing the Archean and Proterozoic lithosphere of western North America. GSA Today 8, 16–17. Ito, T., 2002. Active faulting, lower crustal lamination and ongoing Hidaka arc–arc collision, Hokkaido, Japan. In: Fujikawa, Y., Yoshida, A. (Eds.), Seismotectonics in Convergent Plate Boundary. TERRAPUB, Topyo, pp. 219–224. Ito, T., Iwasaki, T., Thybo, H., 2009. Deep seismic profiling of the continents and their margins — preface. Tectonophysics 472 (1–4), 1–5. Iwasaki, T., Yoshii, T., Ito, T., Sato, H., Hirata, N., 2002. Seismological features of island arc crust as inferred from recent seismic expeditions in Japan. Tectonophysics 355 (1–4), 53–66. Iyer, H.M., Pakiser, L.C., Stuart, D.J., Warren, D.H., 1969. Project Early Rise; seismic probing of the upper mantle. J. Geophys. Res. 74 (17), 4409–4441. Janik, T., Kozlovskaya, E., Heikkinen, P., Yliniemi, J., Silvennoinen, H., 2009. Evidence for preservation of crustal root beneath the Proterozoic Lapland-Kola orogen (northern Fennoscandian shield) derived from P and S wave velocity models of POLAR and HUKKA wide-angle reflection and refraction profiles and FIRE4 reflection transect. J. Geophys. Res. 114 doi:10.1029/2008JB005689. Kato, N., et al., 2004. Has the plate boundary shifted from central Hokkaido to the eastern part of the Sea of Japan? Tectonophysics 388 (1–4), 75–84. Kind, R., et al., 2002. Seismic images of crust and upper mantle beneath Tibet: evidence for Eurasian plate subduction. Science 298 (5596), 1219–1221. Klemperer, S.L., 1987. A relation between continental heat flow and the seismic reflectivity of the lower crust. J. Geophys. 61 (1), 1–11. Klemperer, S.L., Hobbs, R.W., 1992. The BIRPS Atlas: Deep Seismic Reflection Profiles Around the British Isles. Cambridge University press. 128 pp. and 100 seismic sections. Klemperer, S.L., Mooney, W.D. (Eds.), 1998a. Special Issue — Deep Seismic Profiling of the Continents, I: General Results and New Methods: Tectonophysics, 286, pp. IX–XIV. Klemperer, S.L., Mooney, W.D. (Eds.), 1998b. Deep Seismic Profiling of the Continents, II: A Global Survey: Tectonophysics, 288, pp. VII–VIII. Knott, C.G., 1899. Reflexion and refraction of elastic waves wth seismological applications. Philos Mag. 48, 64–97. KRISP Working Party, 1991. Large-scale variation in lithospheric structure along and across the Kenya rift. Nature 354 (6350), 223–227. Kukkonen, I.T., Lahtinen, R., 2006. Finnish Reflection Experiment FIRE 2001–2005. Geological Survey of Finland: Special Paper, Espoo. 247 ppp. + 15 app. + CD-ROM pp. Lamb, H., 1904. On the propagation of tremors over the surface of an elastic solid. Philos. Trans. R. Soc. Lond. A203, 1–42. Levander, A., et al., 1994. The crust as a heterogeneous “optical” medium, or “crocodiles in the mist”. Tectonophysics 232, 281–297. Leven, J.H., Finlaysson, D.M., Wright, C., Dooley, J.C., Kennett, B.L.N. (Eds.), 1990. Seismic Probing of Continents and their Margins: Tectonophysics, 173. Lewis, B.T., Meyer, R.P., 1968. A seismic investigation of the upper mantle to the west of Lake Superior. Bull. Seis. Soc. Am. 58 (2), 565–596. Lie, J.E., Pedersen, T., Husebye, E.S., 1990. Observations of seismic reflectors in the lower lithosphere beneath the Skagerrak. Nature 346 (6280), 165–168. Lyngsie, S.B., Thybo, H., Lang, R., 2007. Rifting and lower crustal reflectivity: a case study of the intracratonic Dniepr–Donets rift zone, Ukraine. J. Geophys. Res. 112, B12402 doi:10.1029/2006JB004795. Mackenzie, G.D., Thybo, H., Maguire, P.K.H., 2005. Crustal velocity structure across the Main Ethiopian Rift: results from two-dimensional wide-angle seismic modelling. Geophys. J. Int. 162 (3), 994–1006. Makovsky, Y., et al., 1996. INDEPTH wide-angle reflection observation of P-wave-to-Swave conversion from crustal bright spots in Tibet. Science 274 (5293), 1690–1691. Mallet, R., 1852. Second report on the facts of earthquake phenomena. Report of the Twenty-first Meeting of the British Association for the Advancement of Science, pp. 272–320. Masse, R.P., 1973. Compressional velocity distribution beneath central and eastern North America. Bull. Seis. Soc. Am. 63 (3), 911–935. Matthews, D.H., 1982. Birps — deep seismic-reflection profiling around the British-Isles. Nature 298 (5876), 709–710. Matthews, D.H., Smith, C. (Eds.), 1987. Deep Seismic Reflection Profiling of the Continental Lithosphere: Geophys. J.R. Astron. Soc., 89. 447 pp. Mechie, J., et al., 1993. P-wave Mantle Velocity Structure beneath Northern Eurasia from Long-range Recordings along the Profile Quartz. : Structure and Evolution of the European Lithosphere and Upper Mantle; 7th Conference of the European Union of Geosciences, 79. 1–2, pp. 269–286.
Editorial Meissner, R., 1967. Exploring deep interfaces by seismic wide angle measurements. Geophys. Prospect. 15, 598–617. Meissner, R., et al. (Ed.), 1991. Continental Lithosphere: Deep Seismic Reflections: Am. Geophys. Union, Geodyn. Ser., 22. 450 pp. Meissner, R., Rabbel, W., Kern, H., 2006. Seismic lamination and anisotropy of the lower continental crust. Tectonophysics 416 (1–4), 81–99. Mjelde, R., Faleide, J.I., Breivik, A.J., Rauma, T., 2009. Lower crustal composition and crustal lineaments on the Vøring Margin, NE Atlantic: a review. Tectonophysics 472 (14), 183–193. MONA LISA Working Group, 1997. MONA LISA; deep seismic investigations of the lithosphere in the southeastern North Sea. Tectonophysics 269 (1–2), 1–19. Morozova, E.A., Morozov, I.B., Smithson, S.B., Solodilov, L., 2000. Lithospheric boundaries and upper mantle heterogeneity beneath Russian Eurasia: evidence from the DSS profile QUARTZ. Tectonophysics 329 (1–4), 333–344. Nelson, K.D., et al., 1996. Partially molten middle crust beneath southern Tibet; synthesis of Project INDEPTH results. Science 274 (5293), 1684–1688. Nielsen, L., Thybo, H., Solodilov, L., 1999. Seismic tomographic inversion of Russian PNE data along profile Kraton. Geophys. Res. Lett. 26 (22), 3413–3416. Nielsen, L., Thybo, H., Egorkin, A.V., 2002. Implications of seismic scattering below the 8 degrees discontinuity along PNE profile Kraton. Tectonophysics 358 (1–4), 135–150. Okada, H., et al., 1979. Regionality of the upper mantle around northern Japan, as revealed by big explosion at sea: I. SEIHA-I explosion experiment. J. Phys, Earth 27, S15–S32 suppl.. Oliver, J.E., Dobrin, M., Kaufman, S., Meyer, R., Phinney, R., 1976. Continuous seismic reflection profiling of the deep basement, Hardeman County, Texas. Geol. Soc. Am. Bull. 87, 1537–1546. Oncken, O., et al., 1999. Seismic reflection image revealing offset of Andean subductionzone earthquake locations into oceanic mantle. Nature 397 (6717), 341–344. Pfiffner, O.A., Frei, W., Finckh, P., Valasek, P., 1988. Deep seismic reflection profiling in the Swiss Alps; explosion seismology results for line NFP 20-EAST. Geology 16 (11), 987–990. Reston, T.J., Krawczyk, C.M., Klaeschen, D., 1996. The S reflector west of Galicia (Spain); evidence from prestack depth migration for detachment faulting during continental breakup. J. Geophys. Res. 101 (4), 8075–8091. Ross, A.R., Thybo, H., Solidilov, L.N., 2004. Reflection seismic profiles of the core–mantle boundary. J. Geophys. Res. 109 (B8) doi:10.1029/2003JB002515. Ruiz, M., et al., 2006. Seismic activity at the western Pyrenean edge. Tectonophysics 412 (3–4), 217–235. Sandrin, A., Thybo, H., 2008. Seismic constraints on a large mafic intrusion with implications for the subsidence history of the Danish Basin. J. Geophys. Res. 113 (B9) doi:10.1029/2007JB005067. Sato, H., et al., 2004. Formation and shortening deformation of a back-arc rift basin revealed by deep seismic profiling. Tectonophysics 388, 47–58. Snyder, D.B., Eaton, D.W., Hurich, C.A., 2006. Special issue — seismic probing of continents and their margins — introduction. Tectonophysics 420 (1–2), 1–4. Steer, D.N., Knapp, J.H., Brown, L.D., 1998. Super-deep reflection profiling: exploring the continental mantle lid. Tectonophysics 286 (1–4), 111–121. Sultanov, D.D., Murphy, J.R., Rubinstein, K.D., 1999. A seismic source summary for Soviet peaceful nuclear explosions. Bull. Seis. Soc. Am. 89 (3), 640–647. Thybo, H., 2002. Deep seismic probing of the continents and their margins — selected papers from the 9th biennial meeting held in Ulvik, Norway. Tectonophysics 355 (1–4), 1–5. Thybo, H., 2006. The heterogeneous upper mantle low velocity zone. Tectonophysics 416 (1–4), 53–79.
5
Thybo, H., Nielsen, C.A., 2009. Magma-compensated crustal thinning in continental rift zones. Nature 457, 873–876 doi:10.1038/nature07688. Thybo, H., Perchuc, E., 1997. The seismic 8 degrees discontinuity and partial melting in continental mantle. Science 275 (5306), 1626–1629. Thybo, H., Perchuc, E., Zhou, S., 2000. Intraplate earthquakes and a seismically defined lateral transition in the upper mantle. Geophys. Res. Lett. 27 (23), 3953–3956. Thybo, H., Nielsen, L., Perchuc, E., 2003a. Seismic scattering at the top of the mantle Transition Zone. Earth Plan. Sci. Lett. 216 (3), 259–269. Thybo, H., Ross, A.R., Egorkin, A.V., 2003b. Explosion seismic reflections from the Earth's core. Earth Plan. Sci. Lett. 216 (4), 693–702. Tsumura, N., et al., 1999. Delamination-wedge structure beneath the Hidaka collision zone, central Hokkaido, Japan inferred from seismic reflection profiling. Geophys. Res. Lett. 26, 1057–1060. Warner, M.R., 1990. Basalts, water, or shear zones in the lower continental crust? Tectonophysics 173 (1–4), 163–174. Warner, M., et al., 1996. Seismic reflections from the mantle represent relict subduction zones within the continental lithosphere. Geology 24 (1), 39–42. Warren, D.H., et al., 1968. Project Early Rise travel times and amplitudes. U.S. Geol. Surv., Open-File Rep., Menlo Park. 150 pp. Wernicke, B., 1981. Low-angle normal faults in the Basin and Range Province; nappe tectonics in an extending orogen. Nature 291 (5817), 645–648. White, D.J., Ansorge, J., Bodoky, T.J., Hajnal, Z., 1996. Special issue — seismic reflection probing of the continents and their margins — preface. Tectonophysics 264, R7–R9. White, R.S., Smith, L.K., Roberts, A.W., Christie, P.A.F., Kusznir, N.J., 2008. Lower-crustal intrusion on the North Atlantic continental margin. Nature 452 (7186), 460-U6. Yoshii, T., Asano, S., 1972. Time-term analysis of explosion seismic data. J. Phys. Earth. 20, 47–57. Yuan, X., et al., 2000. Subduction and collision processes in the Central Andes constrained by converted seismic phases. Nature 408 (6815), 958–961.
H. Thybo⁎ Department of Geography and Geology, University of Copenhagen, Øster Voldgade 10, DK-1350 Copenhagen K, Denmark ⁎Corresponding author. E-mail address: [email protected]. P. Heikkinen Institute of Seismology, PL 68, Gustaf Hällströmin katu 2b, FI-00014 University of Helsinki, Finland I. Kukkonen Geological Survey of Finland (GTK), Betonimiehenkuja 4, FI-02150, Espoo, Finland 28 September 2010