Investigating P- and S-wave velocity structure beneath the Marmara region (Turkey) and the surrounding area from local earthquake tomography

Gulten Polat,Ivan Koulakov,Nurcan Meral Özel

doi:10.1186/s40623-016-0503-4

Abstract

We investigated the crustal structure beneath the Marmara region and the surrounding area in the western part of the North Anatolian fault zone. These areas have high seismicity and are of critical significance to earthquake hazards. The study was based on travel-time tomography using local moderate and micro-earthquakes occurring in the study area recorded by the Multi-Disciplinary Earthquake Research in High Risk Regions of Turkey project and Kandilli Observatory and Earthquake Research Institute. We selected 2131 earthquakes and a total of 92,858 arrival times, consisting of 50,044 P-wave and 42,814 S-wave arrival times. We present detailed crustal structure down to 50 km depth beneath the Marmara region for P- and S-wave velocities using the LOTOS code based on iterative inversion. We used the distributions of the resulting seismic parameters (Vp, Vs) to pick out significant geodynamical features. The high-velocity anomalies correlate well with fracturing segments of the North Anatolian fault. High seismicity is mostly concentrated in these segments. In particular, low velocities were observed beneath the central Marmara Sea at 5 km depth.

Highlights

The Eurasian and Arabian–African plates apply a continuing compressional force on the Anatolian plate (Sengor and Yilmaz 1981)
In this study, we collected data from permanent and temporary stations deployed by TUBITAK during the TURDEP and Kandilli Observatory and Earthquake Research Institute (KOERI) in order to investigate the P- and S-wave velocity structure beneath the whole Marmara region and western Turkey
Our observations suggest that the local earthquake tomography (LET) has been successfully applied to measure P- and S-wave velocity variations for the whole Marmara region

Summary

Introduction

The Eurasian and Arabian–African plates apply a continuing compressional force on the Anatolian plate (Sengor and Yilmaz 1981). Another study (Karabulut et al 2003) used a 2D tomographic seismic velocity image in the eastern Marmara region along a N–S trending seismic refraction profile that traverses the Cinarcık Basin in the Sea of Marmara (see Fig. 1a) Most of these studies were based on the inversion of P- and S-wave travel time arrivals from local seismicity recorded by stations belonging to temporary and/or permanent networks. It is significant that the same algorithm was used for data processing both in the present and in the mentioned study This might suggest that for an a priori indicator of the amplitude of the velocity anomalies, it is possible to use the rms of the initial residuals.

Discussion

Findings

Conclusion