Seismotectonics of the northeastern margin of the Arabian plate in Iraq

The objective of this research is to study the seismotectonics of the Bitlis-Zagros Fold and Thrust Belt in northern Iraq and surrounding regions. This was accomplished through studying the crustal seismic velocity structure, focal mechanism solutions, and stress pattern of the study area. The joint inversion of receiver functions and surface wave dispersion, the moment tensor inversion, and formal stress inversion of moment stress axes are among the methods used to study the seismotectonic patterns of the study area. Another goal of this study is to provide a regional velocity model and pre-computed Green's functions that can be used accurately to determine the moment tensor solutions for this and future research in the same study area.;The crustal structure beneath the Duhok seismic station in the northwestern part of Iraq was estimated by the joint inversion of receiver functions and surface wave dispersion. The results show that the crustal structure has three distinct discontinuities. The upper discontinuity represents the sedimentary column with a thickness around 8 km; the middle represents the Conrad discontinuity with a depth of 22 to 24 km, and the lower represents the Moho discontinuity with a depth of 40 to 42 km. This velocity model was modified and used to calculate Green's functions for northern Iraq and surrounding regions.;The waveform moment tensor inversion method was used to derive focal mechanism solutions of 65 earthquakes with magnitudes of ≥3.5 in the study area. The seismic data of these events were collected from 54 broadband seismic stations, which belong to different seismic networks. The results show that the most common tectonic regimes are strike-slip (43.94%), unspecified oblique (27.27%), and thrust (13.64%) regimes. In most cases, the strike-slip movement on fault surfaces is of left-lateral (sinistral).;The dataset of the moment stress axes (P, N, and T), which were calculated from the focal mechanism solutions, have been used to infer the regional principal stress axes (sigma1, sigma2, and sigma3) by the formal stress inversion method. The results show that the horizontal stress axes at the Bitlis-Zagros suture zone have two directions. One is perpendicular to the suture zone near the Iraq-Iran border and the second is parallel in places as well as perpendicular in others to the suture zone near the Iraq-Turkey border.