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Determination of elastic wave velocity and relative hypocenter locations using refracted waves. II. Application to the Haicheng, China, aftershock sequence

U.S. GEOLOGICAL SURVEY, BOX 25046, MS 966DENVER FEDERAL CENTER, DENVER, COLORADO 80225
DEPARTMENT OF EARTH, ATMOSPHERIC AND PLANETARY SCIENCES MASSACHUSETTS INSTITUTE OF TECHNOLOGY, CAMBRIDGE, MASSACHUSETTS 02139
U.S. GEOLOGICAL SURVEY SEISMOLOGY LABORATORY CALIFORNIA INSTITUTE OF TECHNOLOGY, PASADENA, CALIFORNIA 91125
INSTITUTE OF GEOPHYSICS STATE SEISMOLOGICAL BUREAU, BEIJING, People's Republic of China

Abstract

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 x 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.

This article has been cited by other articles:

				K. M. SHEDLOCK and S. W. ROECKER Determination of elastic wave velocity and relative hypocenter locations using refracted waves. I. Methodology Bulletin of the Seismological Society of America, April 1, 1985; 75(2): 415 - 426. [Abstract] [PDF]