Source properties of micro - earthquakes in eastern Marmara and their connection to the structure of the Çınarcık basın

Abstract

This study mainly focuses on the source properties of micro-earthquakes in Eastern Marmara and their connection to the structure of the Çınarcık Basin, in particular. Throughout this study, Prince Islands Real Time Earthquake Monitoring System (PIRES) Arrays data have been used, which is the closest land site locations to the North Anatolian Fault (NAF) in the Marmara Sea. Only a limited number of small magnitude earthquakes occur in the Çınarcık Basin. Therefore, earthquakes only within an epicentral distance of ~20 km to the arrays have been evaluated considering that Signal to Noise Ratio (SNR) decreases abruptly for further distances. Special methods have been developed and adapted to the PIRES in this study. In this context, advantages of the arrays have been used in all aspects. Array based cross correlation method has been developed for the optimal detection of the small magnitude events which show similarity. Using this method, a systematical search of the foreshocks and aftershocks activities has been performed. This has led to a large improvement of the detection level and revealed large number of earthquake clustering. It became possible to extract many small magnitude events that are buried in the background noise or in the coda of previous events and therefore were missed by the land stations. Since, the main target was to evaluate the performance of the surface arrays against the boreholes, various noise cancelation tools are developed based on the stacking of repetitive observations. These procedures are used for the estimations of the fracture properties of the small events inside the Çınarcık Basin. The fracture properties that have been analyzed are the seismic moment, fracture radius, stress drop, energy and occurrence statistics. Tests are performed to see if the fracture properties are changing in space and time, or show any other characteristic behavior that may be connected to a particular location in the study area. Variations are observed between the stress drop and location of the events. Similarly, foreshock and aftershock occurrence statistics seems also to vary across the Çınarcık Basin. Since, the present data is rather restricted, it is expected that the interpretations are only preliminary. The results obtained imply that this type of analysis will probably be part of the real time monitoring processes in the future, for the purpose of early warning systems.