Iranian Journal of Geophysics

Iranian Journal of Geophysics

Reapprisal of seismotectonics of northwest Iran and east Turkey

Document Type : Research Article

Authors
Salman Andayeshgar 1
Abdolreza Ghods 2
,Esmaeil Shabanian 3
Jochen Braunmiller 4
1 Ph.D. Student, Department of Earth Sciences, Institute for Advanced Studies in Basic Sciences, Zanjan, Iran
2 Professor, Department of Earth Sciences, Institute for Advanced Studies in Basic Sciences, Zanjan, Iran
3 Associate Professor, Department of Earth Sciences, Institute for Advanced Studies in Basic Sciences, Zanjan, Iran
4 Associate Professor, University of South Florida
10.30499/ijg.2025.528165.1706
Abstract
To investigate the seismotectonics of NW Iran and East Turkey using the multi-event hypocentroid decomposition method, 12 seismic clusters comprising 2,149 relocated earthquakes were analyzed. Among these, 688 earthquakes were assigned focal depths with uncertainties of 2–3 km, and 234 focal mechanisms were calculated for these events. In this study, all available datasets were utilized to examine correlations between known active faults and their associated seismicity and mechanisms, identify potential new faults, estimate the mechanisms of active faults in the region and finally revise the kinematic deformation model of the region. The results confirm that the primary tectonic boundaries defined in NW Iran and East Turkey, along with their associated mechanisms, remain largely valid, with most seismicity concentrated along block boundaries. However, intra-block seismicity is observed within parts of the NW Iran and Van blocks. The seismicity pattern indicates that the majority of the seismic activity is concentrated along the right-lateral strike-slip North Tabriz Fault and its continuation toward the Gailatu-SiahCheshmeh-Khoy and Chalderan fault systems. Instrumental records reveal that seismic activity has persistently affected most segments of these faults over time. Our findings highlight a prominent and concentrated seismicity trend with normal mechanisms extending from the Zagros Mountains toward Salmas. Additionally, another seismicity trend with right-lateral strike-slip mechanisms is observed, initiating at the terminus of the Zagros Main Recent Fault System and extending toward southeast Anatolia. Furthermore, two newly identified trends perpendicular to the North Tabriz Fault, with a northeast orientation, emerge in the data. These may indicate the presence of fault segments characterized by left-lateral strike-slip mechanisms, which partially accommodate the displacement along the North Tabriz Fault. The distribution of aftershock cloud and variety of their focal mechanisms indicate that the fault geometry and mechanism in Khoy are more complex than the existing simplified fault maps suggest. Notably, the right-lateral strike-slip mechanisms along the Talesh–South Caspian boundary as proposed in earlier tectonic models were not observed. Similarly, the relocated seismicity does not show any seismic activity along the south Baskale fault or the Maragheh fault. Based on earthquake focal depths and focal mechanisms, we hypothesize that faults parallel to the western Caspian fault are responsible for deep strike-slip earthquakes with a transtensional component in the Kura Basin. The intermediate-depth events may suggest underplating of northwestern region of SCB beneath Kura basin. The focal and centeriod depths indicate that the depth of the earthquakes along the primary boundaries of tectonic blocks ranges from 10 to 12 kilometers. However, within the blocks, specifically in the Ahar-Varzeqan cluster, as well as in the Zagros region, including the Oshnaviyeh and Bashkal clusters the depth of earthquakes is larger. This may be due to the young and immature nature of the faults responsible for these earthquakes. Additionally, the depth of earthquakes in the Talesh region and the South Caspian Basin may exceed 40 kilometers, indicating seismic activity occurring within the cold igneous crust of the South Caspian Basin lying beneath a thick sedimentary cover.
Keywords
Seismicity, relocation, tectonics, NW Iran, east Turkey

Subjects

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Iranian Journal of Geophysics
Volume 20, Issue 1
March and April 2026
Pages 111-146

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