abstract

Two Ms = 7 earthquakes struck in April and May of 1976 near the town of Gazli, Uzbekistan in the Soviet Union causing extensive damage. The focal mechanisms of the two events have been determined by modeling the long-period body waves with synthetic seismograms. Both events have large components of thrust faulting, but they vary measurably in azimuthal orientation. The moment of the first event was 2.1 × 1026 dyne-cm and of the second was 2.4 × 1026 dyne-cm. The stress drops were around 50 bars which is typical for intraplate events.

The surrounding region had been assigned a low seismic risk based on recent patterns of seismicity. Historic records from the ancient city of Bukhara show that earthquakes in the magnitude range 6 to 7 had actually occurred in the region several times prior to the turn of the century. The Gazli events appear to have occurred on a preexisting zone of weakness that is evidenced by the geological record.

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