Fracture Anisotropy Characterization and Lateral Effects from Azimuthal Resitivity Survey in Alqosh Plain- North Iraq

Abstract

Alqosh plain lies about 40 km to the north of Mosul city surrounded by several Taurus anticlines (E-W direction). The anticlines are separated by a wide syncline underlying the plain .The M-U Eocene rocks are exposed in the core of those anticlines which are overlain by Fat'ha, Injana and Meqdadya Formations. The field survey of the earth resistance measurements was carried out at three locations (Alqosh, Boawzan, Bayban) in the study area, depending upon some geomorphological, geological and geotectonic features. Three azimuthal directions are used appling Offset Wenner Array (OWA) with fifteen spacing intervals. The OWA survey was represented by cartesian and polar graphs depending on the calculated mean percentage. The results displayed pseudo electrical anisotropy representing by lateral variations at small electrode spacings, while electrical anisotropy effects are shown in large spacings.. The present study indicated varied fractures having frequencies, directions and dips that are parallel and vertical to the structural axes with vertical and medium dips. as well as, minor and medium fractures extending for several spacings. The current study showed large frequency fractures that are inclined to the fold axes especially in Alqosh and Bawzan. In addition, an inverse relationship appeared between electrical anisotropy frequencies and lateral variations in the study area.