Integrated seismic and geodetic strain analysis in the Kopeh Dagh Belt (Northeastern Iran): Implications for intraplate deformation

Abstract

The Kopeh Dagh mountain belt is one of the most tectonically and seismically active regions in the central Eurasian collision zone, having experienced numerous moderate to large earthquakes (Mw ≥ 5.1) in recent decades. This study presents a novel structural and geodynamic analysis of ongoing deformation in the Kopeh Dagh Belt through the integration of GPS velocity vectors and earthquake focal mechanisms. A new methodological framework was developed by discretizing the region into 20 triangular grids, allowing for high-resolution spatial comparisons between seismic and geodetic strain tensors. This approach enables localized assessment of strain accumulation and release patterns. Using earthquake focal mechanism data spanning 1969 to 2024 and GPS measurements from 2016 to 2020, we derive the orientations and magnitudes of the maximum principal strain rates. The results identify distinct zones of strain concentration along major fault systems, including the Sangerd, Doruneh, Kurkhod, Esfarayen, and Kalateh Arabha faults. Areas with elevated geodetic strain and significant clockwise rotation rates are closely associated with active strike-slip faulting. Stress regime classification reveals a predominance of strike-slip (41.82%) and thrust faulting (38.18%), with minor contributions from normal faulting. A consistent pattern of lower seismic strain rates compared to geodetic strain rates suggests ongoing stress accumulation and elevated seismic hazard potential. This research introduces an innovative, grid-based approach to deformation partitioning and offers new insights into the seismotectonic behavior of an intraplate mountain belt, with broad implications for seismic hazard assessment in complex continental interiors.