由地震反射波剖面研究圣安德烈斯断层带的结构
INTERPRETATION OF SEISMIC REFLECTION PROFILING DATA FOR THE STRUCTURE OF THE SAN ANDREAS FAULT ZONE
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摘要: 1978年,在美国中加利福尼亚完成了一条横跨圣安德烈斯断层带的地震反射波剖面.由于断层带存在着强烈的侧向非均匀性和低速结构,观测结果极为复杂.这种断层带上的侧向速度急剧变化还有其它表征,诸如震中定位的偏移、地震节平面的变形等等.在这种情况下,处理反射波资料的常规计算与解释方法,已经难以实施.本文采用 May 和 Covey(1981)[11]的射线反演方法,根据其它地球物理资料建立初始模型,再利用真实振幅的迭加剖面,推断出其阻抗对比的分布,通过反复迭代反演,获得了速度模型.反演计算的非唯一性固然存在,但该结果与断层带地区的各种地球物理证据是一致的,并揭示了圣安德烈斯断层带的细致结构.Abstract: A seismic reflection profile crossing the San Andreas fault zone in central California was conducted in 1978. Results are complicated by the extreme lateral heterogeneity and low velocities in the fault zone. Other evidence for severe lateral velocity change across the fault zone lies in hypocenter bias and nodal plane distortion for earthquakes on the fault. Conventional interpretation and processing methods for reflection data are hard-pressed in this situation. Using the inverse ray method of May and Covey (1981), with an initial model derived from a variety of data and the impedance contrasts inferred from the true-amplitude stacked section, an iterative inversion process yields a velocity model which, while clearly non-unique, is consistent with the various lines of evidence on the fault zone structure.
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[1] Aki, K. and Lee, W. H. K., Determination of three——dimensional velocity anomalies under a seismic array using P——arrival times from local earthquakes: 1. A homogeneous initial model, J. Geophys.Res., 23, 4381——4399, 1976.
[2] Aric,K., Gutdeutsch, R,and Sailer, A., Computation of travel times and rays in a medium of two——dimensional velocity distribution, Pageoph, 118, 796——806, 1980.
[3] Boore, D. M. and Hill,D. P., Wave propagation characteristics in the vicinity of the San Andreas Fault, Proceedings of the Conference on Tectonic Problems of the San Andreas Fault System, Stan——ford Univ. Publ., 13, 215——224, 1973.
[4] Chauqui, L. and McEvilly, T. V., Detailed crustal structure within the central California large——scale.seismic array, in Annual Report, Seismographic Station, University of California, Berkeley, 1968.
[5] Clymer, R. W. and McEvilly. T. V., Travel——time monitoring with VIBROSEIS, Bul乙Seism. Soc. Am.71, 1902——1927, 1981.
[6] Eaton, J. P., Lee, W. H. K. and Pakiser, L. C., Use of microearthquakes in the study of the me——chanics of earthquake generation along the San Andreas fault in central California, Tectonophysics, 9,259——282, 1970.
[7] Engdahl, E. R. and Lee, W. H. K., Relocation of local earthquakes by seismic ray tracing,J. Geophys.Res, 81, 4400——4406, 1976.
[8] Ellsworth, W. L., Bear Valley, California, earthquake sequence of February——March 1972, Bull. Seism Soc. Am, 65 483——506, 1975.
[9] Healy, J. and Peake, L., Seismic veloeity structure along a section of the Andreas fault near Bear Valley, California, Bull. Seism. Soc. Am, 65, 1177——1197, 1975,
[10] Lin, W. and Wang, C. Y., P——wave velocities in rocks at high pressure and temperature and the constitution of the central California crust, Geophy. J. R. Astr. Soc, 61, 379——400, 1980.
[11] May, B. T. and Covey, J. D., An inverse ray method for computing geologic structures from seismic reflections——Zero——offset case, Geophysics, 46, 268——2$7, 1981.
[12] McEvilly,T. V,Crustal structure estimation within a large scale array, Geophys.].R. Astr. Soc, 11,13——17, 1966.
[13] McEvilly, T. V., Extended reflection survey of the San Andreas fault zone, U. S. Geol. Sutv. Open——File Report No. 81——388, 1981.
[14] McEvilly, T. V. and Clymer, R. W., A deep crustal reflection survey on the San Andreas fault, EOS Trans. Am. Geophys. Union 56, 1021, 1975.
[15] McLaughlin, K. L., Spatial coherency of seismic waveforms, Ph, D. Thesis, Univ. of California, Ber.keley, 1982.
[16] McNally, K. C. and McEvilly, T. V., Velocity contrast across the San Andreas fault in central Cali——forma: small——scale variation from P——wave nodal plane distortion, Bull. Seism. Soc. Am, 67, 1565——1576, 1977.
[17] Mooney, W. D. and Luetgert, J. H., A seismic refraction study of the Santa Clara Valley and Southern Santa Cruz mountains, West——central California, Bxa1l. Seism. Soc. Am. 72, 901——909, 1982.
[18] Walter, A. W. and Mooney, W. D., Crustal structure of the Diablo and Gabilan ranges, central Cali——fotnia:. a reinterpretation of existing data, Bull. Seism. Soc. Am, 72, 1567——1590. 1982.
[19] Stierman, D. J. and Zappe, S. D., Lateral P——velocity gradients near major strike——slip faults in Cali——forma, Science, 213, 207——209, 1981.
[20] Wang, C. Y:, Lin, W. and Wu, F. T., Constitution of the San Andreas fault zone at depth, Geophys.Res. Lett, 5, 741, 1978.
[21] Wesson, R. L., Travel——time inversion for laterally inhomogeneous crustal velocity models, Bull. Seism.Soc. Am., 61, 729——746, 1971.[1] Aki, K. and Lee, W. H. K., Determination of three——dimensional velocity anomalies under a seismic array using P——arrival times from local earthquakes: 1. A homogeneous initial model, J. Geophys.Res., 23, 4381——4399, 1976.
[2] Aric,K., Gutdeutsch, R,and Sailer, A., Computation of travel times and rays in a medium of two——dimensional velocity distribution, Pageoph, 118, 796——806, 1980.
[3] Boore, D. M. and Hill,D. P., Wave propagation characteristics in the vicinity of the San Andreas Fault, Proceedings of the Conference on Tectonic Problems of the San Andreas Fault System, Stan——ford Univ. Publ., 13, 215——224, 1973.
[4] Chauqui, L. and McEvilly, T. V., Detailed crustal structure within the central California large——scale.seismic array, in Annual Report, Seismographic Station, University of California, Berkeley, 1968.
[5] Clymer, R. W. and McEvilly. T. V., Travel——time monitoring with VIBROSEIS, Bul乙Seism. Soc. Am.71, 1902——1927, 1981.
[6] Eaton, J. P., Lee, W. H. K. and Pakiser, L. C., Use of microearthquakes in the study of the me——chanics of earthquake generation along the San Andreas fault in central California, Tectonophysics, 9,259——282, 1970.
[7] Engdahl, E. R. and Lee, W. H. K., Relocation of local earthquakes by seismic ray tracing,J. Geophys.Res, 81, 4400——4406, 1976.
[8] Ellsworth, W. L., Bear Valley, California, earthquake sequence of February——March 1972, Bull. Seism Soc. Am, 65 483——506, 1975.
[9] Healy, J. and Peake, L., Seismic veloeity structure along a section of the Andreas fault near Bear Valley, California, Bull. Seism. Soc. Am, 65, 1177——1197, 1975,
[10] Lin, W. and Wang, C. Y., P——wave velocities in rocks at high pressure and temperature and the constitution of the central California crust, Geophy. J. R. Astr. Soc, 61, 379——400, 1980.
[11] May, B. T. and Covey, J. D., An inverse ray method for computing geologic structures from seismic reflections——Zero——offset case, Geophysics, 46, 268——2$7, 1981.
[12] McEvilly,T. V,Crustal structure estimation within a large scale array, Geophys.].R. Astr. Soc, 11,13——17, 1966.
[13] McEvilly, T. V., Extended reflection survey of the San Andreas fault zone, U. S. Geol. Sutv. Open——File Report No. 81——388, 1981.
[14] McEvilly, T. V. and Clymer, R. W., A deep crustal reflection survey on the San Andreas fault, EOS Trans. Am. Geophys. Union 56, 1021, 1975.
[15] McLaughlin, K. L., Spatial coherency of seismic waveforms, Ph, D. Thesis, Univ. of California, Ber.keley, 1982.
[16] McNally, K. C. and McEvilly, T. V., Velocity contrast across the San Andreas fault in central Cali——forma: small——scale variation from P——wave nodal plane distortion, Bull. Seism. Soc. Am, 67, 1565——1576, 1977.
[17] Mooney, W. D. and Luetgert, J. H., A seismic refraction study of the Santa Clara Valley and Southern Santa Cruz mountains, West——central California, Bxa1l. Seism. Soc. Am. 72, 901——909, 1982.
[18] Walter, A. W. and Mooney, W. D., Crustal structure of the Diablo and Gabilan ranges, central Cali——fotnia:. a reinterpretation of existing data, Bull. Seism. Soc. Am, 72, 1567——1590. 1982.
[19] Stierman, D. J. and Zappe, S. D., Lateral P——velocity gradients near major strike——slip faults in Cali——forma, Science, 213, 207——209, 1981.
[20] Wang, C. Y:, Lin, W. and Wu, F. T., Constitution of the San Andreas fault zone at depth, Geophys.Res. Lett, 5, 741, 1978.
[21] Wesson, R. L., Travel——time inversion for laterally inhomogeneous crustal velocity models, Bull. Seism.Soc. Am., 61, 729——746, 1971.
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