Abstract

The fault parameters of the Gazli, USSR, earthquake of 19 March 1984 Ms = 7.0 were determined from the inversion of the GDSN long-period P and SH and short-period P seismograms. The frequency of the short-period seismograms was broadened by partially deconvolving the effect of the recording instruments. The earthquake represents a thrust fault with a small amount of a left-handed strike-slip component on a NE-SW trending fault dipping northwest. The average depth is 9 km. The rupture propagated essentially continuously while breaking several high stress asperities. Directivity of the observed waveforms indicates principal rupture direction from SE to NW. The total duration of rupture is about 13 sec. The average scalar seismic moment found from the long-period wave-forms is 2.5 × 1019 N-m.

In addition to the 1984 event, the Gazli region experienced two large (Ms = 7.0) earthquakes in 1976 and one medium size earthquake (Ms = 5.7) in 1978. The mechanisms of the 1976 events were studied by Hartzell (1980) and Kristy et al. (1980), and are thrust events striking in the general E-W direction. We determined the mechanism of the 1978 earthquake and find it similar to those of the 1976 earthquakes. An interesting feature of the Gazli earthquake sequence is the migration of activity from east to west along an arc shaped fault zone. Prior to 1976, the region was relatively aseismic, based on instrumental and historical seismicity data.

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