Focal Mechanisms and Stress Variations in the Caucasus and Eastern Turkey from Constraints of Regional Waveforms
Abstract
The continental collision between Arabia and Eurasia created large strike-slip faults in Turkey, uplift of East Anatolia and mountains in Caucasus. In previous studies, focal mechanisms in the Caucasus are determined primarily for large earthquakes using global waveform data. Small earthquakes are less studied and poorly constrained due to limited stations. In this study, we use regional waveforms of new array to constrain the focal mechanisms and depths of the earthquakes with M>3.5 in the major seismic zones in the Greater Caucasus, Javakheti Highland (Lesser Caucasus) and eastern Turkey. Earthquakes in Racha of the Greater Caucasus are mainly thrust events with strikes in E-W direction confined in the upper to middle crust. Focal mechanisms and distribution of the 2009/09/07 earthquake sequence clearly show that they are the deeper reactivation of the 1991 Racha rupture fault zone. As for the earthquakes in the eastern Turkey and southern Armenia, they are upper crustal strike-slip events. Three of them may be directly associated with Sengaya-Gole fault in the eastern Turkey. Several focal mechanisms are determined in the Javakheti volcanic highland where swarms of small earthquake are continuously occurring. Except for a few small thrust events north of the swarm area, other earthquakes in this region are dominated by strike-slip faulting which disagree with normal structure inferred from the surface expression. With our and Global-CMT results, the formal stress inversion show that the maximum stress (S1) is consistently in 7-14°N direction for the entire study region, which is apparently controlled by the northward movement of Arabia. In the Greater Caucasus, the W-E median stress (S2) is considerable comparing to the N-S S1, allowing both sub-EW and sub-NS striking thrust events to occur. As for the eastern Turkey, the vertical S2 are more comparable to W-E minimum stress (S3), such that the major strike-slip earthquakes coincide with a few thrusting events. Stress ratio in Javakheti region is similar to that of eastern Turkey but the S2-S3 girdle is much pronounced, suggesting that the permutation between the two stress axes is unstable.
- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2013
- Bibcode:
- 2013AGUFM.T23E2632T
- Keywords:
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- 8164 TECTONOPHYSICS Stresses: crust and lithosphere;
- 7230 SEISMOLOGY Seismicity and tectonics;
- 8107 TECTONOPHYSICS Continental neotectonics;
- 7200 SEISMOLOGY