Abstract
In this study, the decay of earthquake aftershock sequences of some major earthquakes in different tectonic regimes in the Iranian plateau is discussed. The studied earthquakes are Rigan [2010], Ahar-Varzaghan [2012], Goharan [2013], Sefidsang [2017] and Ezgeleh [2017]. The spatial and temporal windows are considered based on the method proposed by Gardner and Knopoff [1974] to compute decay parameters for each sequence. The decay rates of sequences were compared to well-known models to find the best fit for each sequence. The results showed that the modified Omori is the best fit for Ahar-Varzaghan and Ezgeleh sequences, for Rigan and Sefidsang sequences the modified Omori and the Kisslinger ones found as the best fits. The values of the p parameter of the Reasenberg and Shcherbakov models were larger compared to the Omori model, but the parameter of the Kisslinger model was slightly smaller compared to the Omori one. The c parameter showed an inverse relation to the threshold magnitude. The correlation between the p and c parameters and also the and the Gutenberg and Richter (G-R) parameters were investigated. In addition, we made use of a graphical method to analyze the seismic sequence of the Ezgeleh earthquake during 13 months after the main event. The graphical method was successful to estimate the occurrence of an event with an approximate magnitude of M=6.4 in the sequence.
Highlights
Seismic sequences are referred to as a series of earthquakes in a region that occur over a certain period of time
We examined the impact of different values of threshold magnitudes and the behavior of their aftershock sequences is compared with different decay models; Omori [1894] which later modified by Utsu [1961], Reasenberg and Jones [1989], Kisslinger [1993] and Shcherbakov et al, [2004]
Our study shows that the Kisslinger or the modified Omori models are the best-fitted decay rates to the aftershock sequences of selected large earthquakes in Iran
Summary
Seismic sequences are referred to as a series of earthquakes in a region that occur over a certain period of time. Gasperini and Lolli [2009] performed a comparison between decay rate models in Southern California and Italy based on the modified Omori model, the modified Kisslinger model and the band limited power law. More recent studies on the spatial and temporal analyses of the distribution of aftershock sequences carried on in different parts of the world; Wiemer and Katsumata [1999], Bayrak and Öztürk [2004], Öztürk et al [2008], Nuannin et al [2012] and Öztürk and Şahin [2019]. Ansari [2017] studied the spatial and temporal seismicity parameters, stress state and seismic energy of the Shonbe earthquake sequence. The first primary and secondary aftershocks are proposed for the most recent sequence of Ezgeleh 2017, applying a graphical method proposed by Riga and Balocchi [2016]
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