Earthquake Hazard ZONING by Fuzzy Logic in Dehek Area (South Khorasan)

In Southern Khorasan Province (East of Iran), due to the operation of active faults (North-South, East-West and North-West-South-east faults), we see earthquakes with different magnitudes. To reduce damage, it is important to determine areas with high seismic potential. Although accurate prediction of this great natural hazard is not possible definitively, it is possible to determine the probable location of the occurrence of an earthquake so the zoning necessity is apparent. The reliability of this map largely depends on the quality of available data, the scale of the study, the choice of a method and the proper modeling. Examples of these methods are using the AHP method and fuzzy logic. The study area is located in the Sistan structural province, which studies the active faults in this area along with the earthquakes that occurred, indicating that the area is tectonically active. Dehek fault with the northwest-southeastern direction is one of the branches of the western Neh fault and continue to southeast and reaches at Ismail Abad dextral. Investigation of seismotectonic maps (Porkermani, 1997) suggests that this area has high seismic potential and there have been many earthquakes in this area. Based on studies on earthquake density, length of faults in the region, magnitude of earthquakes and earthquakes acceleration, East of Iran has high seismic potential.
Methods and

In this study, six parameters were used including: seismic moment, seismic acceleration, iso- intensity of fractures, distance from faults, strength of units and depth of alluvium maps. Zoning studies indicate that seismic moment and seismic iso acceleration play the most important role in the occurrence of earthquakes in the region. Then the resets were examined by fuzzy logic method and finally the results of the study were analyzed in most seismic hazard maps.
Results and Discuss: In the classic logic, for weighting each factor, parts that are approximately similar in terms of other features and change the agent are considered, and by observing changes in this factor and according to expert opinion, the effect of this on the occurrence of earthquake is compared to the region of factors exclusively.
Weighting is based on knowledge and judgment of the undergraduate. The results of these comparisons were introduced as a matrix to the Expert selection software. At the outlet, the weight of each parameter was determined. Among the factors, the seismic Moment parameter of the highest weight and the lowest absolute weight of the alluvial depth parameter were determined.
In the fuzzy method, the normalization of the frequency ratio of each map using the Expert selection software then the degree of fuzzy membership was determined based on the normalized frequency ratios in the Idrisi software environment. Then, the maps prepared on the basis of fuzzy operators were overlapped in ARC GIS software and final output was prepared as zoning map. Output maps obtained on the basis of fuzzy operators show that . Output maps based on fuzzy algebraic (sum) is highly adapted to the fact that 20, 28, 26, 16 and 10 percent of the region is of very low, low, medium, high, and very high risk classes.

In this zoning, firstly, the factors influencing the creation of earthquakes were provisioned and prioritized. Among the factors, the seismic torque parameter had the highest weight, the erosion parameter, and the depth of alluvium. The low weight of the erosion and alluvial factors is due to the fact that most of the high-seismic focus area in the region at a focal depth of less than 12 km is due to the performance of the underlying faults, so the impact of these factors is low. Based on the seismic acceleration parameter, the acceleration that the Dehek fault enters the villages of that area is 0.58 gravitational gravity. According to the Fuzzy algebraic operator function, about 70% of the decay area is in a very high risk area. Also according to the community map, 100% and according to the fuzzy share map, 15% of the district is in high and very high risk classes. Finally, in the fuzzy zoning map to a radius of 150 km, the greatest risk of earthquakes around the Nehbandan, Sahl Abad, Dehek, Chahar Farsakh, Ardakoul and Mazhan faults is at high risk.