Evaluation of tectonic activity effect in the Zagros fold and thrust belt by seismic/geodetic moment rate ratio

In this study, an improved picture of the ongoing crustal deformation field for the Zagros as an evolving foreland fold and thrust belt is presented by using an extensive combination of geodetic and seismic analysis. The significant amount of oblique Arabia–Eurasia convergence is currently absorbed within the Zagros. Part of the total available energy is used in seismic deformations and part of it is stored in faults as potential energy. The remaining energy is consumed by the creeps and aseismic processes. Estimation of moment rate is comparatively reckoned as a new method for investigation of tectonic activities rate in different regions. In this research, geodetic moment rate (based on the GPS data) and seismic moment rate (based on the historical and instrumental earthquake data) are estimated for Zagros block in S-SW of Iran. Each approach has its own limitations. In all parts of the Zagros belt, the maximum estimated moment rate belongs to geodetic moment rate which is almost equal to 7.441×1019 Nm/yr. The seismic moment rate in Zagros belt is almost equal to 3.438×1018 Nm/yr. In this study, different parts of the Zagros Mountain range are investigated using three methods (structural, tectonosedimentary and 1°×1° grid) and the results are compared and analyzed. The seismic moment rate of simply-folded belt, high Zagros and Khuzestan plain are 1.56 × 1018 Nm/yr, 1.45 × 1018 Nm/yr and 6.24 × 1016 Nm/yr, respectively. It means that the maximum (minimum) released energy belongs to simply-folded belt (Khuzestan plain). In Izeh, Central Lorestan, interior Fars and Bandar Abbas hinterland sub-zones, the maximum amount of energy has been released during the earthquakes. The ratio of the seismic moment rate to geodetic moment rate is near 0 (0.0429) which indicates that the aseismic processes dominate the deformation, or stress accumulation is underway which can increase the level of the seismic hazard. Such aseismic deformation is probably related to the presence of the weak evaporitic Hormuz Series that prevents the occurrence of very large aseismic motion. According to the values of geodetic moment rates in the Zagros sub-zones and based on the value of the released seismic energy in the north and northeast part of the study area, it seems that in the future, the most of the seismic potential energy and seismic hazard are in the southeastern part of Zagros belt in Fars and Bandar Abbas hinterland and a part of Khuzestan sub-zone. Our study has implications for better comprehending the current seismotectonic pattern of Zagros fold and thrust belt as an evolving deformation area.