Fault Source of Seismicity in Al-Refaei District, Southern Iraq

Abstract

Over the past two decades, the Al-Refaei district, a substantial town located in the Thi-Qar governorate in southern Iraq, has been subjected to numerous small to moderate-size earthquakes. A network of seven short-period seismic stations was installed in the Al-Refaei district to monitor seismic activity, a project that was initiated in 2014 and continued until 2018. The short-period seismic stations supplement the broadband seismic stations of the Mesopotamian Seismological Network (MPSN), which also serves this area. During the monitoring period, more than 56 earthquakes were recorded, of which 31 were detected by the short-period seismic stations and not reported by any other local or international seismic observatories. Data from the short-period and broadband seismic stations were analyzed using Geiger’s least-squares method to determine accurate locations. The relocated earthquakes delineate a possible fault source with a northwest-southeast trend. The possible fault is not related to any known or previously studied fault. 3D seismic data of the area were evaluated and further supported the interpretation of a northwest-southeast trending fault, named the Al-Refaei fault. Integration of the seismological and 3D seismic data suggests that the Al-Refaei fault is a reverse fault with a S62˚E strike direction and a 43˚ dip angle. The strike and dip of the Al-Refaei fault were calculated from the analysis of the 3D seismic data. The reverse style of faulting was derived from the composite first motion method using the seismic station records of the short-period network.