Seismotectonics of the Bitlis–Zagros Fold and Thrust Belt in Northern Iraq and Surrounding Regions from Moment Tensor Analysis WATHIQ ABDULNABY, 1 HANAN MAHDI, 2 NAZAR M. S. NUMAN, 3 and HAYDAR AL-SHUKRI 4 Abstract—Northern Iraq represents part of the convergent plate boundary between the Arabian and Eurasian plates. The collision zone between these two plates is manifested by the Bitlis–Zagros Fold and Thrust Belt. This belt is one of the most seismically active regions among the present active belts. This study intends to improve our knowledge on the seismotectonic activities in northern Iraq and the surrounding areas. To reach this goal, we used the waveform moment tensor inversion method to determine the focal depths, moment magnitudes, fault plane solutions, and directions of the principal stress axes of 25 events with magnitudes C3.5. The seismic data of these events were collected from 54 broadband stations which belong to the Kandilli Observatory and Earthquake Research Institute, the Incorporated Research Institutions for Seismology, the Observatories and Research Facilities for Euro- pean Seismology, and the Iraqi Seismological Network. Computer Programs in Seismology, version 3.30 (HERRMANN and AMMON 2004), was used for analysis. The results show that the focal depth of these events ranged from 15 to 25 km in general. The fault plane solutions show that the strike-slip mechanism is the most dominant mechanism in the study area, usually with a reverse component. The stress regime shows three major directions; north–south, northeast-southwest, and east–west. These directions are compa- rable with the tectonic regime in the region. 1. Introduction Northern Iraq represents part of the convergent plate boundary between the Arabian and Eurasian plates (Fig. 1). The Eurasian plate consists of two plates, namely, the Anatolian and Iranian plates in the north and northeast of the studied region, consecu- tively. The collision between these plates began after the closure of the Neo-Tethys Ocean in the Miocene. This collision continues to the present day (e.g. DEWEY et al. 1973;NUMAN 1997). The collision has resulted in the formation of the Bitlis–Zagros Fold and Thrust Belt that extends from Turkey and Iraq in the north to the Strait of Hormuz in the south. Geo- logical evidence indicates that the Bitlis–Zagros Fold and Thrust Belt underwent various tectonic episodes that affected different parts of the belt (FALCON 1974; STOCKLIN 1968). The Bitlis–Zagros Fold and Thrust Belt is one of the most seismically active regions among the present active belts (TATAR et al. 2004). This study intends to improve our knowledge on the seismic activities in northern Iraq and the sur- rounding areas. To reach this goal, we used seismic data from 54 seismic stations to estimate the focal depths, moment magnitudes, fault plane solutions, and directions of the principal stress axes of 25 events. We have tried to infer the prevailing mecha- nism of the fault displacements and the stress regime in the study area. Another goal of this study has been to provide a regional velocity model and pre-com- puted Green’s functions that can be used accurately to determine the moment tensor in the Bitlis–Zagros Fold and Thrust Belt in northern Iraq and the sur- rounding regions. 2. Tectonic and Structural Setting The Bitlis–Zagros Fold and Thrust Belt has two distinct trends, NW–SE (here called the Zagros Trend) between the Arabian and Iranian plates, and E–W (called the Bitlis Trend) between the Arabian 1 Geology Department, College of Science, University of Basra, Basra, Iraq. E-mail: wathiq1972@yahoo.com 2 Graduate Institute of Technology (GIT), University of Arkansas at Little Rock, 2801 South University Ave, Little Rock, AR 72204, USA. E-mail: hhmahdi@ualr.edu 3 Engineering and Applied Science, University of Duhok, Duhok, Iraq. E-mail: nazarnuman@yahoo.com 4 Department of Applied Science, University of Arkansas at Little Rock, 2801 South University Ave, Little Rock, AR 72204, USA. E-mail: hjalshukri@ualr.edu Pure Appl. Geophys. Ó 2013 Springer Basel DOI 10.1007/s00024-013-0688-4 Pure and Applied Geophysics