The Role of Tear Faults on the Morphology and Seismic Activity of the Ashkhaneh Fault Zone, Kopeh-Dagh, NE Iran

Document Type : Research Article

Authors

1 Ph.D. Student, Institute of Geophysics, University of Tehran, Tehran, Iran

2 Professor, Institute of Geophysics, University of Tehran, Tehran, Iran

Abstract

The Kopeh-Dagh zone of NE Iran is dominated by active strike-slip and thrust faults that accommodate a part of the convergence between the Arabian and Eurasian Plates. The Ashkhaneh thrust fault zone with approximately 80 km long is one of the main accommodative structures which has been dissected by a number of strike-slip tear faults. Tectonic geomorphology, satellite-based Global Positioning System (GPS), and seismic data imply that the development of tear faults is one of the main controlling factors in structural deformation and related seismic activity along the Ashkhaneh thrust fault zone. The tectonic activity of the Ashkhaneh fault zone is mainly due to the E-W trending range-parallel reverse faults and NE-SW to ENE-WSW trending range-crossing left-lateral strike-slip tear faults coming from two stages. In the first stage, the major E-W trending Ashkhaneh thrust fault zone has been developed in response to the collision of Central Iran with the South Caspian Basin. In the second stage, the progressive N-S shortening resulted in mountain curvature in eastern Alborz and the formation of strike-slip tear faults in response to the differential shortening along the Ashkhaneh fault zone. The sense of slip and geometry of the tear faults and the Ashkhaneh thrust fault seems to provide insights into faults interaction, so that the likely movement along one of these faults may cause reactivation of the other fault(s); similar to the earthquake occurrences on the Shalgun-Yelimsi tear fault (2019/11/07, Mw 5.9) and South Bozgush thrust fault (2019/11/10, Mw 4.4) in northwestern Iran.

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