Tectonic stress around the South Caspian basin deduced from earthquake focal mechanisms

ABSTRACT

In this paper, we study the tectonic stress around the South Caspian Basin (SCB), which includes the Kopeh Dagh, Alborz, Talesh, eastern Greater Caucasus mountain belts, the Apsheron sill, and the Balkhan-Ashkabad fault zone. We apply the stress inversion to focal mechanisms of 410 mainshocks that have occurred over the last 69 years. These mechanisms indicate that the surrounding fault zones of the SCB exhibit diverse types of faulting, ranging from thrust to strike-slip, normal, and their combinations. The results of the stress inversion align with the kinematics of the major fault zones bounding the SCB and emphasize the spatial heterogeneity of the stress field in this region. The region is predominantly under compression, but transpressive and strike-slip regimes are also present. This highlights the role of obliquely oriented basement faults with respect to the maximum horizontal compressive stress (S_Hmax) in accommodating deformation through convergent zones. The orientation of the S_Hmax is in the NE to NNE direction in the Kopeh Dagh, Alborz, Talesh, and Ashkabad-Balkhan fault zones, being rotated to NNE-N in the Greater Caucasus. The orientation of the S_Hmax relative to the convergence direction of the Arabian and Eurasian plates indicates that the Arabian-Eurasian oblique convergence-derived tectonic stress is the primary contributor to the total stress and deformation in this region.

KEYWORDS:

• South caspian basin
• stress
• stress inversion
• focal mechanism

Acknowledgments

We would like to thank the editor and two anonymous reviewers for reviews and their constructive comments that helped to improve this manuscript. We would also like to extend our thanks to Ferdowsi University of Mashhad and the Czech Science Foundation, grant No. 22-10747S (VV) for supporting this research.

Disclosure statement

No potential conflict of interest was reported by the author(s).

Data and codes availability

The Centroid Moment Tensor catalogue (CMT) is available at https://www.globalcmt.org/CMTsearch.html. Other data are available from the Iranian Seismological Center (IRSC) (https://irsc.ut.ac.ir/largevents.php), the International Seismological Centre (ISC) (https://www.isc.ac.uk/iscbulletin/search/catalogue), the Kandilli Observatory and Earthquake Research Institute (https://www.koeri.boun.edu.tr), and the Zurich Moment Tensors catalogue (ZUR_RMT) (https://www.isc.ac.uk/cgi-bin/agency-get?agency=ZUR_RMT). Plotting of the focal mechanism of earthquakes on the Frohlich’s diagram was performed by Orient software developed by Vollmer (2015) (https://www.frederickvollmer.com/orient/index.html). The inversion for stress was performed with open-public Matlab code STRESSINVERSE (https://www.ig.cas.cz/stress-inverse).

Supplementary material

Supplemental data for this article can be accessed online at https://doi.org/10.1080/00206814.2024.2315556

Correction Statement

This article has been corrected with minor changes. These changes do not impact the academic content of the article.

Additional information

Funding

This study was supported by Ferdowsi University of Mashhad. One of co-authors (VV) was supported by the Czech Science Foundation, Grant No. 22-10747S.