Three Dimensional Velocity Structure and Tectonic Features of Armutlu Peninsula

Armutlu Peninsula is located on the Marmara Region in north-western part of Turkey. North Anatolian Fault Zone (NAFZ) is one the most active tectonic structure of the Turkey and also extends across the North of Turkey. Armutlu Peninsula, located on the South-eastern part of the Marmara Region, limited by two branch of NAFZ and significantly affected by this tectonic activity. Especially micro-earthquake activity is rather high in the peninsula. The region has very complex tectonic structure as well as it's seismic activity. The Peninsula also characterized by thermal areas. To better understand the relationship among neo-tectonic features, high micro-earthquake activity and high thermal activity in the peninsula Armutlu Network (ARNET) has been established at September 2005 in and around the Armutlu Peninsula. ARNET is a local seismic network and consist of 1 borehole,1 hydrothermal station and 23 broadband and short period seismometers. In this study, three dimensional velocity structure of the peninsula has been tried to determine by tomographic inversion method to ARNET dataset. The dataset covers between September 2005 and December 2010. Before the tomographic inversion, the dataset has been rearranged. In first stage, earthquakes have been relocated with a one dimensional velocity model, which is accepted for the region. After the relocation, well distributed to the area and high quality earthquakes have been selected by considering as RMS values between 0-0.3, the azimuth gap between 0-180° and stations which has minimum 10 P observations. After the data eliminating process, 685 earthquakes used in tomographic inversion. There is no any magnitude limitation at the earthquakes. For tomographic inversion, last version of the LOTOS code, LOTOS-11 algorithm has been used. In this study, a new one dimensional velocity structure for the local area has been improved as an advantage of the LOTOS code. Than, using this one dimensional velocity model, three dimensional velocity perturbations, absolute velocity structure and Vp/Vs ratio distributions for the Armutlu Peninsula has been determined in good resolution up to 20km depth. The tomographic inversion results, parameters and resolutions have been tested by several test algorithms. After five iterations, tomographic figures show that, the earthquakes occurred in the area, located approximately 15km depth. After 15km depth, number of the earthquakes reduce rapidly. This situation supports the depth of the seismogenic zone at the area. Thermal areas, already known, on Armutlu Peninsula seen in tomographic images clearly. In the tomographic images, sudden velocity transitions have been noticed also. This is thought to be a result of complex tectonic structure and high thermal activity. As well as some new views, obtained results are in good consistence with the previous studies.