Stress Field Inversion Analysis of Earthquake Focal Mechanisms in Northwestern Iran: Implications for Tectonic Regimes

Understanding the stress field is crucial for assessing seismic risks in Northwestern Iran, a region known for its high seismic activity and geological volatility. The intricate tectonic arrangements involving the Arabian, Anatolian and Eurasian plates contribute to the unstable nature of the area. This study focuses on deducing stress regimes through stress inversion analysis of earthquake focal mechanisms in the North Tabriz Fault system. Analyzing the stress field is essential for understanding the elastic characteristics and geodynamics of the region. This study considers the stress field surrounding the Tabriz Fault, aiming to determine stress parameters and principal stress orientations using focal mechanisms. By analyzing ۳۵ earthquake focal mechanism datasets from the Global Centered Moment Tensor and the Iranian Seismological Center, stress field inversions were conducted using Michael's linear inversion method and the iterative joint inversion method. The two techniques yielded distinct outcomes, with the iterative joint inversion method proving more accurate in determining stress fields and principal stress orientations. The Plunge values of  and  were observed to be relatively insignificant, measuring ۳.۲۴ and ۲.۰۶, respectively. A value close to ۹۰ degrees, specifically ۸۶.۱۴, was determined for . The trend values for  and  were found to be ۱۴۶.۰۸ and ۵۵.۹۷, respectively, while  exhibited a trend value of ۲۹۳.۵۱. To estimate the orientation of the maximum horizontal stress (SH), the iterative joint inversion method was employed, yielding an estimation of . The trend and plunge calculated from this method for ,  and  were also utilized in this estimation. The findings indicate the existence of strike-slip faults in proximity to the North Tabriz Fault. The stress direction observed and the trajectory of the fault system suggest the influence of a transpressional mechanism. The predominant right-lateral strike-slip motion observed aligns with the prevailing tectonic regime in the region, providing evidence of strike-slip and thrust faulting stress regimes. The results contribute to a better understanding of the stress field and geodynamic situation in Northwestern Iran. They provide valuable insights for spatial analysis of future earthquakes and assessing seismic hazards in the region.

Keywords:

Stress filed , Focal mechanism , Stress inversion , Horizontal stress (SH) , North Tabriz Fault (NTF)