عنوان مقاله [English]
In this study, Seismic Hazard zoning was probed by studying seismogenic zones and earthquake data in a 150 km radius around the Fars province boundaries in the Zagros seismotectonic zone. Zagros is one of the most seismically active parts of Alpine-Himalayan seismic belt. Fars province located at latitude of 27.2° – 31.42° and longitude of 50.42° – 55.36°, respectively. In this study, seismotectonic zone was determined based on the location of interest, faults strikes, seismic records, and geological structure.
In the first step of process, an earthquake catalogue of the instrumental and historical earthquakes was prepared by assimilating them to a uniform magnitude type (Mw) from 8th century until September 2016. Then, by using the Uhrhammer (1986) and Gardner and Knopoff (1974) methods in 1974, aftershocks and foreshocks were eliminated from the catalogue to have main earthquakes only. After the elimination of aftershocks and foreshocks, 2181 earthquakes remained as the main earthquakes in catalogue and their completeness magnitude was calculated by ZMap software. Afterwards, it was tried to recognize all the active faults around the sites; therefore, 23 area sources were introduced within the studied area from faults, historical and instrumental earthquakes. After introducing area sources, seismic parameters such as beta and lambda were calculated for each part using Kijko software. Similarly, space distribution function portion of each source was calculated. In addition, the results of six magnitude studies utilizing step method carried out by Mousvai et al. (2014) was used in this paper. In the deterministic approach, Pick Ground Acceleration (PGA) over bedrock was computed using two attenuation equations, Campbell and Bozorgnia (2008) and Boor and Atkinson (2008), using a MATLAB software for Fars province. Besides, in the probabilistic approach, PGA and pick ground velocity, PGV, were calculated using the same values in the attenuation equations that were used in the deterministic method using OpenQuake, one of the distinguished programs in seismic hazard analysis to determine the PGA on bedrock. The probabilistic approach was carried out on a grading area using a 10 km zonation map. PGA was calculated and covered 63% and 10% probability of exceedance in one life cycle of 50 and 475 years were presented, and hazard curves were calculated for 50 and 475 years using OpenQuake software. Probabilistic study resulted maximum PGA values in the periods of 50 and 475 years to be 0.23 g and 0.6 g respectively .These maximum PGA values centered on Kazeroon. After Kazeroon, Shiraz and Lamerd have the highest levels of hazard risk of cities in Fars province. Moreover, using the deterministic approach and the two attenuation equations, the obtained maximum PGA values fell between 0.68 g and 0.75 g. Finally, the results were compared with previous studies like Hamzeloo (2005), Ghafory-Ashtiany (1999) and Mousavi (2014).