Introduction
The occurrence of destructive earthquakes has been the cause of many human and financial losses in Iran. With the development of urbanization and construction activities in the vicinity of active faults, the risk of earthquakes has been increasing in recent centuries. Studying the risk of earthquakes and its consequences is an important research field that can be implemented using Geographic Information System (GIS) (Jena et al., 2020). According to the definition, risk is the product of three parameters: hazard, vulnerability, and exposure. The hazard may be potentially harmful to people, property, infrastructure, economic activity, and even the environment, all of which are categorized as elements or assets at risk. Population, buildings, essential facilities, and critical infrastructures can be mentioned among the important elements at risk that should be considered in the risk analysis. Vulnerability describes the characteristics and conditions of a community, system, or asset that expose it to the damaging effects of a hazard. Many GIS-based seismic risk models have been proposed. The Karmania Hazard Model (KHM) is one of these models. Hassanzadeh et al. (2013) presented the KHM to assess the seismic risk of Kerman City.
In this study, KHM was combined with probabilistic seismic hazard analysis in order to benefit from the advantages and capabilities of the PSHA in KHM. In this way, the capability of the proposed method to provide realistic analyses of earthquake risk will be improved. The proposed method has been tested in Behbahan Urbun dacay. To this end, we calculated the earthquake risk in the urban decay and prepared the seismic risk maps of the area.
The study area
Historical data shows the occurrence of destructive earthquakes in the Behbahan region. These earthquakes have destroyed the old Behbahan region (Arjan) and left many losses. Following this earthquake, the village of Behbahan, which was located at a distance of about 8 kilometers from Arjan, gradually welcomed the people and turned into a settlement and prosperity, which finally showed itself as a Behbahan city in history in the 8th century. The occurrence of frequent earthquakes and the location of numerous small and large faults in the surrounding area of Behbahan show the seismic potential of this city (Zolfegharifar and Bosak, 2016).
According to the 2015 census, Behbahan city has a population of about 122,604, of which 12,551 (about 10%) live in the worn texture of the city. Also, most of the commercial activities of the city are located in this sector. The total area of the residential part of the city is 22.3 km2and the area of worn texture is 1.7 km2 (7.6% of the area of the urban area).

Methodology
In this research, the basis of risk calculation is based on the KHM. For this purpose, the acceleration of the ground on the bedrock will be determined by combining the KHM and the PSHA (Cornell-McGear approach). The site effects are considered by a well-known method on the acceleration of the bedrock and the acceleration on the ground surface is determined. Then, the acceleration is applied to the buildings and the damage limits are determined based on the fragility curves. Finally, according to the population living in each building, the Loss of human life is estimated. The proposed method includes three main steps, as follows :
- Earthquake risk analysis considering the local site effects (seismic hazard microzonation)
- Determining the vulnerability of buildings and facilities
- Investigating the exposure (people and assets)


Analysis, Results and discussion
The maximum acceleration (PGA) in the region was calculated using Open Quick software. The average estimated value of PGA for the 475-year return period of Behbahan city is equal to 0.32. Also, the average estimated value of PGA for the 2475-year return period of Behbahan city is equal to 0.49.
For most building types, the default HAZUS values assume that 10 out of 100 people in the collapsed part of the building will be killed immediately (over 80% damage) and another 5 out of 100 people will be trapped without rapid rescue and immediate treatment ( general condition damage Greater than 60 %) do not survive. These values are based on a variety of general building configurations and the assumption that even with a collapse, most at-risk occupants will be able to exit the structure. In cases where collapse failure is expected to crush or bury building occupants under heavy construction debris (such as concrete or masonry), users should modify the loss rate. In such cases, the loss rate for general damage above 60% should be increased by a factor of 2 (for localized collapse including heavy debris) to 5 (for complete pancake collapse of floors) (Hazus, 1999).
Based on HAZUS, in the damage above 80%, road closure, and the heavy debris, the minimum amount of casualties for high damage is multiplied with a factor of 2 (i.e., 30% of the residents) and for complete damage with a factor of 5 (i.e., 75% of the residents). In the design and severe earthquakes, it is estimated that more than 3765 and 9413 people are killed, respectively.


Conclusion
For a return period of 475 years, the acceleration on the bedrock is between 0.294g and 0.391g (compared to 0.3g for the 2800 standard). For the return period of 2475 years, this acceleration is in the range of 0.439g and 0.618g. The results of the risk analysis show that for the planned earthquake, about 45% of the buildings will be completely damaged and other existing buildings will also reach the category of severe damage. In a severe earthquake, all the buildings in this section will be completely destroyed. According to the residents of the area, the casualties in the design earthquake are 3,765 and in the severe earthquake are 9,413.