The Role of Geoelectrical DC Methods in Determining the Subsurface Tectonics Features. Case Studies from Syria

Abstract

The tectonic and faulted zones are characterized by a pronounced change in rock physical properties, where the application of geophysical methods allows directly detecting and delineating such zones. The geoelectrical DC methods are the most appropriate for characterizing the tectonic and faulted zones. Different DC configurations have been developed for the location of tectonic and faulted zones, such as combined resistivity profiling, (Mares et al., 1984). In the last few years, a large number of high-resolution seismic reflection surveys have been conducted ( e.g., Williams et al.,1995; Palmer et al., 1997; Van Arsdale et al., 1998 to provide information on Quaternary fault geometry and timing. For very shallow investigation, ground-penetrating radar (GPR), which can bridge the gap between high-resolution seismic surveys and trenching, has been applied by Cai et al. (1996) in the San Francisco Bay region. Although, the GPR yields a highresolution picture down to 4 to 6 m, but the high number of GPR reflections and diffractions resulting from complex sedimentary and tectonic features does not usually permit an unambiguous location of fault, (Demanet et al. (2001). However, when the fault is delineated by other geophysical methods, the interpretation of GPR data gives valuable information on the deformation pattern close to the fault and its position. At the border of Nevada and California, Shields et al. (1998) have used several geophysical techniques (seismic reflection, magnetic, and electromagnetic) to locate the extension of the Parhump Valley fault zone. Demanet et al. (2001) have also applied various geophysical techniques (electrical profiling, electromagnetic, GPR, seismic reflection) along the Bree fault scrap (Western border of the Roer Graben) in order to locate and image an active fault zone in a depth range between a few decimeters to a few tens of meters. These acquired geophysical data are considered as a reconnaissance tool prior to trenching. Parrales et al., 2003 has executed a site investigation by using combined geophysical methods in a faulted area in Managua, Nicaragua. A mapping of active capable faults by high resolution geophysical methods has been carried out by Chwatel et al., 2005, where several examples from the Central Vienna basin were provided. Caputo et al., 2007, 2003 have characterized