Seismic clustering in the Sea of Marmara: Implications for monitoring earthquake processes

Abstract

Quantifying regional earthquake cluster style is essential for providing a context for studies of seismicity patterns and earthquake interactions. Here, we identify clusters of seismicity in the Sea of Marmara region of the North Anatolian Fault, NW Turkey, using a recently derived high-resolution seismicity catalog and the nearest-neighbor earthquake cluster approach. The detected earthquake clusters are utilized for (1) determining spatial distribution of mainshock and aftershock rates and estimating the proximity to failure on different fault segments, (2) identifying fault sections having earthquake repeaters, and (3) finding areas with enhanced foreshock activity. About 6%, 70% and 24% of the events are identified as foreshocks, mainshocks and aftershocks, respectively, with the largest concentration of aftershocks and foreshocks located along the Western High and the Cinarcik Fault, respectively. The method successfully identifies regions where previous studies reported earthquake repeaters as indicator for fault creep and suggests additional repeater areas in the Gulf of Gemlik. The largest proportion of mainshocks with associated foreshocks and aftershocks are along the Western High and Cinarcik Fault segments, potentially indicating that these segments are closer to failure and have increased susceptibility to seismic triggering. Continuing studies can contribute to monitoring possible preparation phase of a large (M > 7) earthquake in the Marmara region near the Istanbul Metropolitan region.