Abstract
For the last two decades, the District of Al-Refaei, southern Iraq, experienced several small to moderate size earthquakes that seem to be clustered in a relatively small area. The initial locations of these earthquakes from the available local and international bulletins show scattered events without any clear structural patterns. A seven-elements seismic array was installed for the period 2014 to 2018 to monitor this activity. Each element of the array consists of three-component Geospace GS11d high-frequency (4.5 Hz) geophone, a solar system power source, and telemetry communications system to transmit data to a central recording station. During the period of monitoring, the array recorded more than 56 earthquakes having a range of magnitude between 1.5 ML to 4.7 mb. Large number of the low magnitude earthquakes were not detected by other monitoring agencies; however, they were recorded by the array. Fifty-six of the most clearly recorded earthquakes were screened for relocation and analysis. Out of the 56 screened earthquakes, 35 were detected by the array alone. The majority of the selected earthquakes having their initial locations within the array. This improves the relocation process and increase accuracy. The relocated earthquakes express a clear pattern of a linear feature which strikes in the northwest-southeast direction. The direction of the newly inferred pattern coincides with the general tectonic setting of Iraq as it is parallel to Zagros suture zone and the general stress regime of the Arabian Plate. The depth of the relocated earthquakes ranges from about 3.9km to 8.9km. This indicates that these earthquakes occur along a shallow subsurface fault that was not mapped before.
Highlights
Al-Refaei district, southern Iraq, located 80 km north of Nasiriyah City and 300 km south of the capital city, Baghdad
The logical interpretation of such linear feature is that it represents a moderately active fault that is capable of generating swarms of events every few years with some are large enough to cause structural damage
Error ellipse in kilometers may calculated for each event using the Root Mean Squares (RMS) values. 53 out of the 56 relocated earthquakes show error ellipses less than 500 meters (Fig.7)
Summary
Al-Refaei district, southern Iraq, located 80 km north of Nasiriyah City and 300 km south of the capital city, Baghdad. The study area is located between 30.45 – 32.50 latitudes and 45.00 – 47.00 longitudes. The area is agricultural in nature which relies on Al-Gharraf River for irrigation. The area is relatively well-populated by many cities including Al-Neser, Qalat Suker, Al-Fajer and Al-Hay (Fig. 1). The study area, located within the Mesopotamia Plain which is a part of the Arabian Plate, currently under a compressional and uplift stress regime. The Arabian Plate drifted to the northeast and collided with the Iranian micro-plate creating the Zagros-
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