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Source processes of the 1981 Gulf of Corinth earthquake sequence from body-wave analysis

SEISMOLOGICAL DEPARTMENT UPPSALA UNIVERSITY, BOX 120 19, 750 12 UPPSALA, Sweden

Abstract

Teleseismic long-period body waves from the 24 February 1981 Gulf of Corinth earthquake and its two principal aftershocks of 25 February (02h35m) and 4 March (21h58m) 1981 are studied to determine source characteristics. Focal mechanisms, along with observed surface fault breaks, suggest that the Corinth earthquake sequence represents normal faulting due to the N-S trending extension. Depths of the three shocks, estimated by matching synthetic seismograms to observations, are found to lie between 4 and 12 km. The azimuthal variation of observed body-wave duration indicates that the main shock is a multiple event and that the main rupture occurred about 3 to 4 sec after a relatively small foreshock and propagated toward the W-NW.

Seismic moments deduced from the body-wave synthetics are 8.1 x 10²⁵, 2.7 x 10²⁵, and 2.2 x 10²⁵ dyne-cm for the main, 25 February and 4 March shocks, respectively. Average final displacements and stress drops are estimated to be 37 cm and 10 bars for the main shock (for a circular fault of radius 15 km); 22 cm and 8 bars for the 25 February shock, and 18 cm and 7 bars for the 4 March shock (for circular faults of radius 11 km).

The striking features of the earthquake sequence are the low stress drops of the main shock and its two principal aftershocks, and the clear eastward migration of aftershock activities. The unusually long source-time function rise times (4 sec for the main shock, 2.5 sec for both aftershocks) and low stress drops suggest an overall slow energy release during the earthquake sequence.

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