Frequency content analysis of the probable earthquake in Kopet Dagh region—Northeast of Iran

This paper aims to describe a probabilistic frequency analysis procedure to develop seismic hazard maps of Kopet Dagh region in north and northeast of Iran which with mostly shallow earthquakes is a high active seismic area. The existence of Khangiran super gas reservoir increases the importance of this region. By application of the probabilistic methodology of Cornell, an extensive numerical analysis based on several deterministic and probabilistic indices, the frequency content of ground motions recorded during seismic events were carried out by EZFRISK computer code, Matlab programming environment, and generated graphical user interface C# computer code. In this paper, definition of a seismotectonic model of the whole region based on geologic, tectonics, and seismic information the potential seismic sources introduced and their seismic characteristics were determined. Among the different applied attenuation relationships, the proposed one by Ambraseys et al. (J Earthq Eng Struct Dyn 25(4):371–400, 1996) was considered and the results are expressed in a series of contour maps of expected PGA for 63 % probability. The elimination of fore and aftershocks and also put some abilities such as capability for result exporting in several format which can be defined by user for other mathematical generic curve fitting tools were carried out by a generated code in Matlab programming environment. Obtained hazard maps indicated that maximum accelerations will be occurred in northwest-central trend which has a well matching with Quchan-Robat and Esfarayen-Robat Gharabil faults. The relevant frequency analysis showed that form 0.1 to 10 Hz, PGA directly increased by frequency and then up to 20 Hz with a sharpen shape, decreased by frequency increasing. The trend continues by gradual reduction up to 100 Hz. Maximum acceleration will be occurred in the basement in frequency content of 10 Hz.