Seismicity and recent stress regime of Diyala City, Iraq–Iran border

Abstract

Diyala city is one of the most seismically active cities in Iraq. It is located in the northeastern part of Iraq at the Iraq–Iran border. In this study, the seismic history of Diyala during 10 years (2004–2014) has been studied. Three seismic catalogs, which are the EMSC, IRIS, IRSC, were used to study the seismic history of the study area. From the seismic history, six seismic swarms were recognized; these are: January 2005, September 2008, June 2009, August 2009, November 2013, and August 2014. In order to study the stress regime in the study area, focal mechanism solutions of eight earthquakes were collected from the GCMT catalog. Most of the focal mechanism solutions of earthquakes in the study area, that have magnitude 5 and more, indicate reverse movements formed by compressional forces. The study area has faults with different lengths and directions. However, the fault that is responsible of earthquakes with magnitude 5 and more is a reverse fault with strike direction equals 314°, dip direction equals 224°, and dip angle equals 64°. The attitudes of the principal stress axes at that fault surface are: σ1 18°/232°, σ2 10°/139° and σ3 69°/022°. In fact, this fault represents the northwestern part of longer fault, which is Badra-Amarah fault that extends from Amarah city in the southeastern to Mandali city to the northwestern. It is the most seismically active fault in Iraq.