Investigating crustal structure of the Marmara region using local tomography and seismic anisotropy anisotropy methods

Abstract

The crustal structure underneath the Marmara region was investigated by uti lizing local tomography and shear wave splitting methods in this study. These regions have high seismicity and are thus of serious importance to seismic risks. The first part of the research was based on travel-time tomography utilizing local moderate and microseismic events occurring in the study area recorded by the Multi-Disciplinary Earthquake Research in High-Risk Regions of Turkey project and Kandilli Observa tory and Earthquake Research Institute. We had chosen 2,131 seismic events and 92,858 arrival times in total, comprising of 50,044 P-wave and 42,814 S-wave arrival times. The mapped earthquakes were gathered in the segments of the fault that has high seismicity. Low velocities were observed beneath the central Marmara Sea at 5 km depth. Also, the 2006 Mb =5.3 Manyas-Kus Golu (Manyas) earthquake had been ret rospectively “stress-forecasted” utilizing changes in time-delays of seismic shear wave splitting to evaluate the time and magnitude at which tension-modified microcracking reaches fracture criticality within the stressed volume where strain is released. We observed that clear decreases in delay-times before the impending event, especially at the station GEMT are consistent with the anisotropic poroelasticity (APE) model of fluid-rock deformation, but we could not observe similar changes at other stations sur rounding the main event. The logarithms of the duration of the tension accumulation are proportional (self-similar) to the magnitude of the impending event. Although time and magnitude of the 2005 Manyas earthquake could have been stress-forecasted, as has been recognized elsewhere, shear wave splitting does not appear to provide direct information about the location of impending earthquakes.