Using Marine Seismic Data to Investigate Active Plate Boundary Deformation

Using Marine Seismic Data to Investigate Active Plate Boundary Deformation Comparison of two multichannel marine seismic reflection profiles that show remarkably similar structure at the same scale adjacent to: (above) a left-lateral high-angle fault offshore southern California just east of Anacapa Island, and (below) the right-lateral North Anatolia continental transform fault in the Marmara Sea (inset). Neither high-angle fault can explain the adjacent broad, long-wavelength fold. Low-angle (oblique) thrust faults are likely present beneath these adjacent, active folds.
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Significant plate boundary deformation occurs offshore of California and Turkey associated with the San Andreas and North Anatolian fault systems, respectively. In both cases, combinations of low-angle faults beneath long-wavelength folds and adjacent high-angle faults appear to accommodate distributed oblique plate motion and inferred clockwise block rotation. In southern California, predominantly E-W-trending left-lateral faults and associated blind faults and folds of the western Transverse Ranges continue east through the northern margin of Los Angeles basin. Active segments of the North Anatolia fault system in the Marmara Sea are not far from Istanbul. Understanding the nature, geometry, and hazards of this deformation may be best studied where these structures can be well imaged in the subsurface using marine seismic reflection data. The Marmara Sea has been the subject of intensive marine geological and geophysical studies since the devastating and deadly 1999 earthquakes. Similarly, much of the offshore California Borderland was been previously surveyed by industry for its hydrocarbon potential. The strong similarity of the observed deformation in these two areas and the recent availability of some of these offshore data sets suggest that comparative studies of these two areas offers a wealth of potential insights into the fundamental nature and development of active crustal deformation. This includes a better understanding of the relation between faults and fault-related folding, the partitioning of oblique plate boundary strain on low- and high-angle faults, and the accommodation of distributed plate motion through crustal block rotation. Through the efforts of many colleagues at USGS, IRIS, SCEC, and AGI, together with major industry representatives, several important marine seismic data sets along the western margin of United States from California to Alaska are now becoming available through the National Archive of Marine Seismic Surveys (http://walrus.wr.usgs.gov/NAMSS/); and efforts to use these data to investigate the active structures of the California Borderland have already begun.
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Childs, J.R and P.E. Hart, National archive of marine seismic surveys (NAMSS): U.S. Geological Survey program to provide new access to proprietary data, Eos (Trans. AGU), 85, n.47, NG43A-0441, 2004.
Nicholson, C., C.C. Sorlien and J.R Childs, Southern California Imaging Project (SCIP): Archiving and using industry data to evaluate plate boundary deformation, Seismological Research Letters, 75, n.2, p.258, 2004a.
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Nicholson, C., C.C. Sorlien and J.R Childs, GENII: A developing consortium to archive and use industry data to evaluate plate boundary structure, deformation and evolution, 16th Annual IRIS Workshop Program and Abstracts, Tucson, AZ, 2004b.
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Polonia, A., et al., Holocene slip rate of the North An
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Seeber, L., et al., Uplift and Subsidence from Oblique Slip: The Ganos-Marmara Bend of the North Anatolian Transform, Western Turkey, Tectonophysics, 391, pp. 239-258, 2004.
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Sorlien, C. C., and L. Seeber, Comment on “Anatomy of the North Anatolian Fault Zone in the Marmara Sea, western Turkey: Extensional basins above a continental transform” by Aksu et al., GSA Today, 10, p. 41, 2000.
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Work supported in part by NSF award OCE-0327273 (CS) and SCEC awards 075639 (CS) and 083262 (CN).

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