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Faulting mechanisms of the Liyang, China, earthquakes of 1974 and 1979 from regional and teleseismic waveforms—Evidence of tectonic inversion under a fault-bounded basin

Center for Earthquake Research and Information The University of Memphis, Memphis, Tennessee 38152
Department of Geological Sciences The University of Memphis, Memphis, Tennessee 38152

Abstract

The Liyang earthquakes of 1974 and 1979 were two moderately sized but destructive events in eastern China. The first shock (M_s = 5.5) occurred on 22 April 1974 in a densely populated area, and the second one (M_s = 5.7) took place on 9 July 1979 near the same location. The epicenters were located near the intersection of two faults and inside a late Mesozoic to late Tertiary sedimentary extensional basin. In this article, long-period P and SH waveforms between 2° and 90° and short-period teleseismic P waveforms were used to determine strike-slip source mechanisms with large reverse-faulting components that occurred for both events. These mechanisms are significantly different from earlier determined solutions reached through P-wave first motions, which found strike-slip and normal-slip components for the two events. The solution of the 1974 event, obtained from this study, strikes 126°, dips 71°, and slips 33°. The focal depth, seismic moment, and stress drop are determined to be 12 km, 8.4 x 10²³ dyne-cm, and 41 bars, respectively. The mechanism of the 1979 event strikes 41°, dips 64°, and slips 147°. The focal depth, seismic moment, and stress drop are found to be 7.5 km, 1.6 x 10²⁴ dyne-cm, and 152 bars, respectively. Seismic data and local observations suggest that the 1974 event ruptured a WNW-striking fault. For the 1979 event, the fault plane is difficult to resolve. The observed oblique reverse faulting is relatively rare for major earthquakes in eastern China and probably represents a reactivated and inverted fault motion beneath a structural basin under the present-day E-W to ENE-WSW compressional stress field.

Footnotes

¹ Present address: Environmental and Safety Designs, 5724 Summer Trees Dr., Memphis, Tennessee 38134.

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