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Published September 10, 1993 | Published
Journal Article Open

Source complexity of the 1988 Armenian Earthquake: Evidence for a slow after-slip event

Abstract

We analyzed teleseismic P and S waves using a multiple-event deconvolution method to investigate the source process of the Spitak, Armenia, earthquake of December 7, 1988. Teleseismic long-period body waves exhibit complex waveforms, significantly more complex than those normally seen for an event of this size. We identified two groups of subevents. One is a group of strike-slip events during the first 20 s. The other is a dip-slip event initiating at about 30 s after the initial rupture. The tensor sum of all the subevents is essentially strike-slip (strike=302°, dip=59°, rake=143°) with a scalar moment of 1.47×10^(19) N m. The seismic moment of the dip-slip event (strike=89°, dip=60°, rake=88°) is 5.6 ×10^(18) N m, nearly 40% of the total, and the moment release rate is slower than the other subevents with a strike-slip mechanism. We call this event a slow after-slip event. The mechanism of the after-sup event is consistent with the present-day deformation pattern in the Caucasus where north-south compression is predominant due to the continental collision between the Arabian plate and the Russian Platform. This result suggests that in a region where both strike slip motion and crustal shortening are taking place, like southern California, a large strike-slip event may accompany large thrust events and vice versa. In order to determine the total coseismic deformation pattern, it is essential to resolve these multiple events in time, space, and mechanism.

Additional Information

© 1993 The American Geophysical Union. Paper number 93JB01568. Received April 23, 1992; Revised June 1, 1993; Accepted June 8, 1993. We thank Hitoshi Kawakatsu for comments on the nondouble-couple component of the CMT solution. This research was partially supported by U.S. Geological Survey grant 1434-93-G2305, and Grant-In-Aid for Scientific Research 02201106 from the Ministry of Education, Japan. This is contribution 5139, Division of Geological and Planetary Sciences, California Institute of Technology, Pasadena, California.

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August 22, 2023
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