Structure and seismo-tectonic investigation of the Sarigol- Buldan region, Western Anatolia, by using gravity and seismicity data

Abstract

The parameter b (commonly referred to as the b-value) is one of the most significant seismic parameters to describe the seismicity of an investigated region. In this study, the structural framework of the Sarigol- Buldan region located in the intersection area of the western Anatolian graben system in Turkey was investigated by using seismicity and gravity data. As known, western Anatolia is one of the most seismically active regions of the Anatolian plate. Therefore, seismic activity in this region is very high. Analysis of the Bouguer gravity data enabled to define the shallow subsurface structure of the study area. Results from the gravity analysis indicated that the sediment basement depth varied from 0.1 km and 2.1 km. We also detected many NW-SE, E-W, and NE-SW trending lineaments that may be faults or fractures, and the NW-SE trending the Denizli basin lies to the east of the Alasehir basin. We observed that the findings from this analysis seem compatible with the regional geological trend. In addition to this, the seismicity of the region was analyzed by using the frequency-magnitude distribution to find out the seismic hazard risk. The most useful way in the analysis of the seismic hazard studies is to reveal the location of the earthquake boundary, which produces devastating big seismic events because such studies make it possible to forecast the location of possible future earthquakes and improve seismic hazard maps. The b-value for this study region was estimated by using the maximum likelihood method. Variations in the b-value were observed, which range from approximate to 0.2 to 2. A higher b-value was detected in the Buldan horst and surrounding area. In contrast to this, lower b-values were observed in the northeast part of the interaction region between the Denizli and the Alasehir grabens. The positive Bouguer anomaly values as high as +10 mGal and low b-values in the north-eastern part of the study region were interpreted as indicating a thinner crustal root. In comparison, negative Bouguer anomaly values were observed in the Alasehir and the Denizli grabens. Also, in these grabens, intermediate to high b-values were found. This suggests that there is a relation between gravity anomaly and b-value. This relation is strongly related to the normal faulting mechanism existing in the region.