Determination of elastic wave velocity and relative hypocenter locations using refracted waves. II. Application to the Haicheng, China, aftershock sequence
We located the aftershocks of the 4 February 1975 Haicheng, China, aftershock sequence using an arrival time difference (ATD) simultaneous inversion method for determining the near-source (in situ) velocity and the location of the aftershocks with respect to a master event. The aftershocks define a diffuse zone, 70 km × 25 km, trending west-northwest, perpendicular to the major structural trend of the region. The main shock and most of the large aftershocks have strike-slip fault plane solutions. The preferred fault plane strikes west-northwest, and the inferred sense of motion is left-lateral. The entire Haicheng earthquake sequence appears to have been the response of an intensely faulted range boundary to a primarily east-west crustal compression and/or north-south extension. The calculated upper mantle P-wave velocity is 7.6 ± 0.09 km/sec, and the inferred crustal thickness is between 31 and 32.5 km. The low upper mantle velocity and thin crust may be indicative of local lithospheric extension.
Additional Information© 1985 Seismological Society of America. Manuscript received 4 June 1984. We are grateful to K. Aki, S. Cohn, R. McCaffrey, P. Molnar, S. Roecker, R. Stewart, and R. Wesso for their thought-provoking questions and discussions with us. We are also grateful to Gu Gongxu and Xu Shaoxie of the Institute of Geophysics, State Seismological Bureau, Beijing, People's Republic of China, for their encouragement and patience, and for making this work possible. We also wish to thank X. Jiang, the Liaoning Provincial Seismological Bureau, G. Wei, and the Shadong Provincial Seismological Bureau for making us feel so welcome and for sharing their data with us. We also wish to thank S. Luria for her assistance in the preparation of this manuscript, and R. Ricotta and P. McDowell for drafting the figures.
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