IS the closest fault the dangerous fault? Case Study Saveh City

the study area of this study is located in central iran and part of the Urmia-Dokhtar volcanic belt.  It is the oldest rock in the region, depending on the median eocen. there are several earthquakes in this area caused numerous earthquakes. in general, an earthquake risk analysis study consists of several steps that will be addressed in this chapter. Two basic parts are important here. first, the recognition of tectonic Source that includes the recognition of seismic Source and knowledge of their main characteristics.  these features can include length, distance, dip and dip direction, Siesmic potential, active faults, quaternary deposits. The second part deals with the seismic activity of the region. in this part, we identify and analyze the seismic status of the region as we identify prehistoric earthquakes (benefiting from the historical data of seismology). Such investigations resulted in the identification of valuable information, such as the  Siesmic rate of Gutenberg- Richter coefficients, and  seismic pattern. finally, the combination of these two parts in the form of a comprehensive model is modeled as the seismic model and can be considered as input data Research Method.

 in this study, advanced EZ - Frisk software has been used for analyses. since in such studies it is necessary to apply at least a suitable  Atteniuation relation. regard to features and geological conditions,  tectonics and Siesmotectonic of this area  in Iran,  have finally used four new generations to calculate the seismic velocity parameters of the region by considering equal weight for each relationship. the probabilistic approach for determining the Siesmic parameters of this study is the probabilistic approach of risk analysis. in the PSHA method, using probabilistic models from Siesmic Source (point, line, path, or region), the maximum amount of seismicity values of the  pick Ground Acceleration is calculated while using probabilistic models from  Siesmic Sourse (point, line, path, or region).

 Important faults of this area are Alborz, Kushke-e-Nosrat, Indes, qom – Zefreh, and Ipak. the Ipak fault over 100 km, along with east - west, is the most active element of  Siesmotectonic in this range. The earthquake event of 1962 with magnitude 7.2 has occurred as the largest instrument event in the region, relating to the activity of the Ipak fault. Alborz fault, 2 km distance, is the closest Siesmotectonic element to the  Saveh city. this fault has overturned the from south east on quaternary deposit. according to the explanations that have been studied in the study section, the PSHA diagram for the Saveh city is calculated based on Fig. 3. therefore, the 0.22 acceleration for Saveh city is evident in the period of 475 years. The most probable magnitude during the 475  year period is 5 / 5 and at a distance of approximately 21 km. the results clearly show that although Alborz fault is located near the middle of the Saveh city, it is not the main factor in the production of earthquakes for this city and produces only 8.5 percent of total risk. Instead of the Kushk-e-Nosrat and Indes, respectively, at 18 and 21 km, respectively, have 90 % of the risk for the  Saveh city.

 It was thought that the acceleration was the result of Alborz Fault that is almost from the middle of the Saveh city . therefore, the risk separation calculation was performed to determine the validity of this issue. but it was found that the main factor in the earthquake production was not for the city. After magnitude-distance deaggregation analysis, it is clear that the Indes fault with 21 km distance from Saveh city create the 45.12% of hazard within its activity. In fact the controlling earthquake at 475 year return period is associated with Indes fault.