عنوان مقاله [English]
Spatial Analysis of Vulnerability Clusters in Physical Texture of Gorgan city against Earthquake Using Spatial Statistics
Earthquake is one of the most natural hazards dangerous, destructive and unpredictable of the city. According to the country's Crisis Management Organization, 78% of the country's surface is in high seismic risk area and 10% of human-caused mortality is due to earthquake disasters. Golestan province, except the second-ranking provinces, is the earthquake hazard and in its category the first high-risk area. In general, four main theories are related to the vulnerability of cities. First, the human ecology theory that has emphasized the unbreakable bonding of biophysical processes and social processes. Second, the theory of political economy, which have integrated macro and micro perspectives and provides a better analytical framework for complexity and dependence comprehensive understanding of vulnerability-causing factors. Third, the theory of community-oriented compatibility, this theory is based on Identification, assistance and the implementation of community-based activities that have strengthen the capacity of local people to adapt to life in a risky and unpredictable situation. Fourth, Resilience which is the capacity or ability of the community to predict, prepare, respond and quickly against the effects and consequences of disaster. According to the country's Crisis Management Organization, 78% of the country's area has placed in high-risk seismic zone and 10% of the human losses resulting from the disaster is as a result of the earthquake. Golestan province is among the second-ranking provinces of the earthquake hazard and in its category is province first of high risk. The results of the surveys show that 840 earthquakes have been registered in Golestan and many areas of the province are susceptible to landslide. Seismic zoning maps has show that Golestan province has four zones, regardless of the effect of alluvial deposits. These zones have included of areas with very high, high, medium and low of seismic hazard. Gorgan has located in very very high and high areas. Accordingly, the aim of present research is measurement and spatial analysis of vulnerability clusters in physical texture of Gorgan city in critical conditions in order to points determination of immediate intervention.
Seismic zoning maps for seismic rock placement, based on the background of the accelerated movement of the earth's powerful movement for the return period of 475 and 2475 years, show that regardless of the effect of alluvial deposits, Golestan province has four zones, areas with high, high, medium and The city of Gorgan is low in many areas.
Materials and methods
The current research is applied and its method is descriptive-analytical. Determinants criteria of physical texture vulnerability degree in Gorgan were investigated in five criteria including of number of floors, fineness, age of buildings and materials. After evaluating the criteria and converting them to comparable and standard scales, has been used from Analytic Network Analysis (ANP) for relative weight determination of each criterion. Prioritization of the indicators was done according to expert opinions and evaluation of the indicators. Finally, blocks have been classified with the VIKOR model in terms of vulnerability and was produced the physical vulnerability map of building units at the urban blocks level of Gorgan city. Then, was carried out vulnerable spatial clusters analysis of Gorgan city through the Getis-Ord model.
Results and discussion
The results of the study show that the highest and the least effective factors in the vulnerability assessment of the Gorgan city blocks were related respectively to the index of building materials with weight (0/425), and the index of pettyness with a weight (0/126). Based on the results of the VIKOR model, the highest degree of physical vulnerability is related to the central and somewhat southern parts of Gorgan. Also, the eastern and western regions and somewhat north of the city have a better status in this index. The Hotspot analysis shows clearly the gap between the center, the south and the margins of the eastern and western regions with other parts of the city of Gorgan. As a result, the central and southern regions and the margins of the eastern and western regions of Gorgan are in an inappropriate situation in terms of vulnerability during the earthquake. At the same time, the northern, western and eastern parts of the city have less damage during the earthquake due to the physical characteristics of the building
Researches such as Ródenas et al(2018), Rusydi et al (2017), Ianoș et al (2017), Kushe et al(2017), Mehraban Motlagh and Motamedi (2018) and Paivastehgar et al (2017) has focused on the zoning of vulnerable sites in cities such as Palu, Bucharest, Karonga, Shiraz and Imamzadeh Hasan Tehran. However, the present study has also focused on spatial analysis of the vulnerable zones of Gorgan and the determination of clusters. At the same time, this research has not neglected to focus on vulnerability zoning. The comparative analysis of vulnerability in Gorgan indicate that the central region has less residential units than the peripheral region of Gorgan. Buildings in the central part are more ancient. The periphery buildings have a higher elevation than the center. Also, peripheral buildings are better in terms of access to passages and are wider than the central part of the city of Gorgan. In general, the buildings of peripheral parts are less vulnerable than the central part of the Gorgan city. In this regard, the following suggestions have been made: The establishment of crisis management centers and emergency services in the west and east of the city, preventing congestion, especially in hazardous areas, opening roads and giving incentives to worn-out buildings regeneration by the government and the municipality.
By comparative analysis of vulnerability in Gorgan, it can be concluded that the central area has less residential units than the periphery of the city of Gorgan. Buildings in the central part of the old age are more. The periphery buildings have a higher elevation than the center. Also, peripheral building buildings are better off in terms of access to passages
Keywords: Vulnerability, Vulnerable clusters, Earthquake, Physical texture, Gorgan city.