Introduction

Earthquakes are among the most important natural hazards and have always attracted the attention of researchers and planners due to the unpredictability of their occurrence time and the extent of human, economic, and environmental damages. Therefore, identifying vulnerable zones and determining the factors affecting earthquake risk play an important role in sustainable development planning, crisis management, and reducing the losses caused by this hazard. Heris County in East Azerbaijan Province is considered one of the areas with high earthquake potential due to its specific tectonic location and proximity to active faults in the region. Accordingly, the present study aims to estimate the earthquake risk in Heris County by utilizing GIS capabilities and modern OPA and MARCOS methods, through the integration of criteria affecting earthquake risk using spatial and descriptive data



Methodology

The current study is applied in nature, and the research method is quantitative–analytical. In this study, first, the factors affecting earthquake risk in the study area, including slope, elevation, geology, land use, distance from previous earthquake epicenters, distance from roads, distance from cities and villages, distance from rivers, distance from faults, focal depth, and seismic power, were identified through a review of relevant literature and consultation with experts. In the next step, spatial data layers corresponding to each factor were prepared in a Geographic Information System (GIS) environment. To determine the relative importance of the criteria, the Ordinal Priority Approach (OPA) was used. OPA is a method based on a linear programming model that solves group multi-criteria decision-making problems using ordinal data. Another multi-criteria decision-making technique used in this study is the MARCOS method, which has been shown in recent studies to provide high stability and reliability in complex decision-making problems. Therefore, in this research, the final earthquake risk map was generated using this multi-criteria decision-making approach.



Results and discussion

A comparative analysis of the elevation factor with the final map obtained in this study shows that vulnerable zones are distributed at elevations ranging from 1,450 to 3,082 meters. A comparison between the zonation map and the slope map also indicates that vulnerable areas are mainly located in slope classes of 5% to 80%. Regarding the distance from rivers, it can be concluded that highly vulnerable areas are distributed within 0 to 3,000 meters of river networks, where population centers in cities and villages are also generally located close to water resources. Accordingly, the cities of Heris, Khajeh, Bakhshaysh, and Zarnaq, along with 54 villages in the county, are situated within a distance of 0 to 500 meters from rivers. Land-use analysis is one of the most important criteria in earthquake vulnerability zoning, as the type of land use in each area has a direct impact on the extent of human, financial, and functional losses caused by earthquakes. In Heris County, according to land-use criteria, residential areas, agricultural lands, and rangelands constitute the largest share of areas with high and very high vulnerability.

Earthquake-related natural hazards are recognized as one of the most important factors contributing to the destruction of urban and rural settlements. In Heris , a significant proportion of residential units, particularly in villages, are constructed using traditional materials such as brick, mud, and stone, which have low seismic resistance. A comparison between the distance map of population centers and the vulnerability zoning map indicates that high-risk zones are located in close proximity to these settlements, generally within 0 to 500 meters. Regarding the distance from communication routes, areas identified with high vulnerability potential are mainly situated at relatively greater distances from roads, ranging from 2,500 to 18,000 meters. In terms of geology, it can be stated that highly vulnerable zones are mainly located in upper red formations, including gray clays with distinct layering, marls with a small proportion of siltstone, fine-grained weathered red and green sandstones with weak induration, and a small amount of micro conglomerate to conglomerate, as well as valley terraces and alluvial fans of both upper and lower levels. According to the research findings, zones with very high and high vulnerability are predominantly located within 0 to 5,000 meters of active faults.

The distance from the epicenters of past earthquakes reflects the seismic history of a region. Based on the zoning map obtained in this study, areas with very high and high vulnerability are located in close proximity to previous earthquake epicenters, particularly within a distance of 0 to 1,000 meters. Shallow earthquakes, due to their smaller depth relative to the Earth’s surface, transmit more energy to the surrounding environment and typically cause more extensive damage than deeper earthquakes. According to the results, areas with high and very high vulnerability are associated with focal depths ranging from 4 to 8 km. Furthermore, as earthquake magnitude increases, the extent of the affected area as well as the likelihood of human and economic losses also increases, leading to higher levels of vulnerability. A comparison between the earthquake magnitude map and the vulnerability zoning map shows that the high-risk zones are distributed within a magnitude range of 4.35 to 6.40 on the Richter scale.



Conclusion

The results indicate that the factors of proximity to active faults, sensitive lithological formations, proximity to previous earthquake epicenters, and urban and rural residential areas have the greatest influence on the spatial distribution of earthquake risk and the severity of earthquake-related damage. Furthermore, the final zoning map shows that the cities of Heris and Khajeh, together with 81 villages, are located within areas of high and very high vulnerability, while the cities of Zarnaq and Bakhshaysh, along with 18 villages, fall within the moderate vulnerability class. These findings indicate that a considerable proportion of the county is exposed to significant earthquake risk, highlighting the need for greater attention to urban and rural development management, infrastructure reinforcement, and earthquake preparedness.