ANALYSIS OF THE AFTERSHOCK SEQUENCES OF LARGE EARTHQUAKES IN IRAN

Publish Year: 1398
نوع سند: مقاله کنفرانسی
زبان: English
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SEE08_271

تاریخ نمایه سازی: 23 آبان 1399

Abstract:

Seismic sequences are referred to as series of earthquakes in a region that occur over a certain period of time.Typically, any seismic sequence consists of a main event and its associated events: foreshocks and aftershocks. Aftershock events are associated with smaller magnitudes and with a time interval of between several minutes to severalyears after the main seismic earthquake, and their abundance decreases over time, until the rate seismicity is returned to the seismic level of the background and the process of seismic events reach a stable state (Omori, 1894). In this study, the decay of the earthquake aftershock sequences of some major earthquakes, in different tectonic regimesin the Iranian plateau such as; Rigan, Ahar-Varzaghan, Goharan, Saravan, Sefidsang and Ezgeleh earthquakes, considering different magnitudes of thresholds,Mc , are discussed based on different decay models (Utsu, 1961; Reasenberg et al., 1989; Kisslinger, 1993; Shcherbakov, 2004). After defining spatial and temporal windows based on the Gardner & Knopoff method, the graphs and parameters of each decay rate were computed and analyzed for each sequence. The decay rates of sequences were compared to the well-known models to find the best fit for each sequence. The rate of decreasing is not constant due to the changes in the threshold magnitudes. The best fit of the decay rates with the studied earthquakes data are in accordance with the threshold magnitude obtained from the Gutenberg-Richter relation. In addition, we studied thedependence of the parameters of the Omori law on the size of the threshold magnitudes. Figure 1, depicts the p and c parameters of the Omori law versus different threshold magnitudes for the studied earthquakes. We seek answer to the question if there is a correlation between the studied parameters in each time interval and the threshold magnitude? In this regard, the correlation between the , c and , b parameters for the studied earthquakes were analyzed for different time windows and presented in Figure 2.

Authors

Mahdieh LAVASANI

M.Sc. Graduate, Institute of Geophysics, University of Tehran, Tehran, Iran

Elham SHABANI

Assistant Professor, Department of Seismology, Institute of Geophysics, University of Tehran, Tehran, Iran