Present-day crustal deformation of the Caucasus and Northern Iran constrained by InSAR time series  

Abstract

The Caucasus and Northern Iran lie within the central part of the Alpine-Himalayan belt, where the Arabian and Eurasian plates started colliding over 100 My ago and caused the building of mountain chains associated with complex tectonics, including transform faulting systems. The region contains many tectonic features including the EW-trending Greater Caucasus and the NW-trending Lesser Caucasus thrust belt separated by the Kura basin. In the southern part of the region, the tectonics are complicated by the Anatolia-Eurasia-Arabia triple junction and the northern end of the Talysh and Alborz thrust belts. There have been several destructive earthquakes in the region, including the Shamakhi earthquake sequences in 1667(8) and 1902 at the junction of the controversial and mostly a-seismic West-Caspian Fault and the Eastern Greater Caucasus and the 1721 and 1780 earthquakes on the North Tabriz fault in NW Iran.  Investigations of the few publicly available seismic catalogs of the region have been insufficient to understand the seismo-tectonic behavior of the regional structures due to sparse existing seismic networks. To better characterize the active structures in the Caucasus and  Northern Iran we produced  regional-scale mean line-of-sight velocity maps and time-series of the surface displacement from the north-eastern Caucasus to northern Iran. To obtain this dataset we performed Synthetic Aperture Radar interferometry using the NSBAS processing (Doin et al., 2011) of Sentinel-1 images along both ascending and descending tracks for 9-years (2015 to 2023). Main processing steps (such as atmospheric correction, multilooking and filtering) were applied to counter biases and loss of coherence due to the snow and vegetation coverage in the Greater Caucasus mountains. We produced two regional-scale interseismic velocity maps that highlight crustal motions of the large-scale tectonic structures. Moreover, we have identified coseismic deformation due to the 5.2 ml Shamakhi earthquake in the SE Caucasus mountains (Feb. 2019), the 5.9 Mw Torkamanchay earthquake in the Bozgush mountains of NW Iran (Nov. 2019), and possible aseismic strike-slip along the West Caspian fault after the large seismic events in Türkiye in February, 2023. Our results can also be used to study the local deformation of mud volcanoes in the Eastern part of Azerbaijan.