Temporal properties of aftershock sequences of large earthquakes in Iran - Analysis of primary and secondary aftershocks of the Ezgeleh sequence

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.

SEISMIC PERFORMANCE OF SCHOOL BUILDINGS IN 2017 EZGELEH EARTHQUAKE, IRAN

Due to the high number of students and the possibility of a high death toll during an earthquake, school buildings are considered as highly important structures in most of today’s seismic codes. The constituents of the structures of these buildings including the load bearing walls and the steel/ concrete components have to be designed so that they are at least capable of life-safety structural performance in the face of strong earthquakes. Meanwhile, due to their significant effects on the response of the structure, the performance of load-bearing and infill walls is particularly important. Observations from educational facilities after the Ezgeleh earthquake of November 12th, 2017 have revealed that the school buildings with unconfined load-bearing wall structural system located in near and far fields of the earthquake have sustained the highest level of damage. Schools with steel and reinforced concrete (RC) structural systems have fared much better in terms of seismic performance and damage. In this study, in addition to the specifications of the 2017 Ezgeleh earthquake, the structural systems and the infill walls used in the educational facilities in the earthquake – affected areas are introduced. Then, the performances of different school buildings with varying structural systems located in the far and near fields of the earthquake were investigated. The results obtained from field observations have been summed up and presented.