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TIME-DEPENDENT SEISMICITY ALONG THE NORTH ANATOLIAN FAULT ZONE

G. F. Karakaisis

Abstract

The time-dependent seismicity along the North Anatolian Fault Zone (NAFZ, 38В°-42В°N, 23В°-42В°E) is examined by means of the Decelerating-Accelerating Seismic strain release (D-AS) model. The model relies on observations of decreasing Benioff strain release several years before a strong earthquake, in the vicinity of the fault to be ruptured (seismogenic region), and increasing strain release in a broader area around this fault (critical region). Both patterns are manifested by moderate magnitude earthquakes (preshocks), which occur in distinct space, time and magnitude windows. For the needs of this study, a recently compiled earthquake catalogue of the broader area of NAFZ is used. This catalogue is produced by combining information of regional and international seismological centers and is homogeneous in respect to the magnitudes of earthquakes as they are all expressed in the moment magnitude scale (original or equivalent after a proper converting procedure). The purpose of this work is twofold. Firstly, as a blind test, an attempt is made to identify decelerating and accelerating seismicity patterns prior to strong earthquakes that occurred during the last 15-20 years and, secondly, to search for such patterns which may probably be associated with future strong earthquakes. Specifically, all mainshocks with M?6.0 which occurred in the examined area during 1999-2016 were considered and a grid search (grid step: 0.2В°) was performed aiming at identifying precursory patterns (decelerating-accelerating seismicity) which may had started several years before their occurrence (e.g. since 1990). We found that several of the target earthquakes (including the 1999 Izmit event) had been preceded by decelerating seismicity. Such seismicity is currently observed in two regions; this phenomenon may foreshadow the generation of strong earthquakes there. The results of such a research can be used as input for time-dependent seismic hazard assessment in the studied area.

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DOI resolver: doi.org/10.5593/sgem2018/1.1/s05.127

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