Seismic zoning of Ardabil city using deterministic hazard analysis and fuzzy system

Zoning and seismic hazard analysis is a powerful tool with useful and valuable information for decision-making. In this study, seismic zoning of Ardabil city on the seismic bedrock level was studied using deterministic hazard analysis method, and fuzzy inference system. The purpose of earthquake hazard analysis is to estimate the strong ground motion parameters in a time period and in a specific site. In all steps of seismic hazard analysis, there are uncertainties that make inevitable use of appropriate methods in seismic hazard assessment. Fuzzy logic is known as a reliable method to evaluate seismic hazards with reliable results in a short time with a simple and flexible process. Iran is one of the most earthquake-prone countries in the world where cities severely suffered during this natural phenomenon. The city of Ardabil with the coordinates of 38.25 North and 48.30 East, is the center of Ardabil province and is located in the northwestern part of Iran. Due to its location among several important active faults with a background of numerous historical destructive earthquakes, its seismicity and hazard analysis seems to be necessary. For this purpose, all the active faults located within a radius of 150 km from the city center along with their seismic history were studied and 20 potential seismic sources were selected for seismic hazard analysis. In the present study, seismic hazard zoning analysis of the Ardabil city is first performed by the conventional deterministic method by meshing the whole area under study with dimensions of 1000 × 1000 meters; then it is performed using the fuzzy inference system for the centers of each mesh, and the results are compared. In deterministic seismic hazard analysis (DSHA), 5 attenuation relationships were used to determine the peak ground acceleration (PGA) and the site-specific response spectrum for the center of each mesh. According to the results obtained by DSHA method, the value of horizontal PGA varies between 0.24g and 0.43g, while using the fuzzy inference system it varies between 0.25g and 0.43g. As a result, the maximum horizontal PGA in this area can be suggested about 0.43g. According to the results obtained from both methods, source No. 3, for which the Bozqoush fault is its main active fault, can be considered the main source potentially causing destructive earthquakes in the future compared to the other sources. Moreover, this source is located at a very close distance to Ardabil city. As well, in general, it can be concluded that the western parts of the city are more prone of sever earthquakes compared to the other parts of the city, and therefore, it is better to build important buildings and infrastructures in areas with lower PGA (eastern parts of the city) and encourage the politicians to urban development to this direction in the future. This study clearly confirms that new techniques such as fuzzy methods can be used to improve and develop the seismic hazards analysis.