عنوان مقاله [English]
On average, an earthquake with the force of 6 magnitude of the Richter scale hits Iran every year and a 7.0 earthquake strikes the country every ten years. The fact that urban areas face serious damages due to these natural disasters makes it clear that a crisis plan is quite necessary. City is a multi-layered structure consisting of closely related physical and non-physical components (functional, spatial, and social) with two levels of interaction among them. Providing a clear understanding of the consequences of hazards and evaluating vulnerable urban areas seem to be a necessary step toward decreased vulnerability to natural hazards. This will be definitely reached through policy making, making the right decisions and taking the right actions. The present study seeks to analyze zoning and vulnerability of Kermanshah metropolis in regard to possible earthquakes. Findings of the present study can be used to prepare an appropriate plan for the future of this city. The present study also explains physical, social and natural components, and uses a combination of these components to prepare different quantitative models and the necessary indicators (basic studies). It also attempts to provide methods of implementing these models and indicators (operational methods). And finally it seeks to prepare a hazard map to facilitate the identification of critical areas and impenetrable residential zones in Kermanshah metropolis, while determining optimal directions for future physical-spatial development of Kermanshah based on seismic risk zone. This is achieved through a new approach using Analytic hierarchy process.
GIS and multi-criteria decision making methods are used in the present study for seismic zoning of natural, physical, social, and economic dimensions of Kermanshah. To reach this end, statistical, non-statistical and online sources were used and necessary maps were collected from relevant organizations and departments. In general, 1, 25000 topographic maps (AutoCAD Versions), Parcel maps of the 2016 census, land use maps showing the present situation (AutoCAD Versions), and etc. were used in the present study. Except for parcel map which was prepared in Shapefile (a well-known format prepared in ARCGIS software) and thus ready for GIS analysis, other layers were prepared in CAD format and had to be edited, revised, and then converted to Coverage format and Shapefile for final editing in GIS models. It is noteworthy that many of these maps were completed and edited by the authors. Then, maps required for each cluster were standardized using the classification method. Related weights and pairwise comparison matrix were defined for each cluster using scientific resources.
Results and Discussion
Due to the large number of sub-indicators used in the present study, each indicator was rated and graded separately. Results indicate that Kermanshah metropolitan area enjoys a desirable status regarding the economic indicator since69.6% of the city lies in the low vulnerability range of this indicator. Regarding the social indicator, the city is in an unfavorable status since56.6% of its area lies in a very high vulnerability range and only a small percentage of the city area (1.5%) lies in the low vulnerability range. Regarding the physical indicator, 57% of the city lies in the medium vulnerability range and 33.2% in the low vulnerability range. Regarding the natural indicator, 55.4% of the city lies in the medium vulnerability range, 36.5% in the high vulnerability range, 1.8% in the very high vulnerability range, and 6.3% in the low vulnerability range. The unfavorable status of the social indicator is due to the presence of areas facing high or very high levels of vulnerability. Findings of the economic indicator imply the distribution of an economic class with an average income in the city. Regarding the physical indicator, about 30% of the city area is covered by old vulnerable settlements constructed with unsustainable materials in direct contrast with urban planning rules. These areas require improvement, reconstruction, and renovation. Regarding the natural indicator, Kermanshah and its neighboring cities are built on earthquake fault lines. Dealing with this situation requires strengthening and modernization of old urban contexts, increasing permeability of arterial roads, development of non-physical spaces, making a greater use of empty spaces, and building new residential spaces (brownfield lands). Findings indicate the significant role of natural factors (including proximity to earthquake fault lines), physical factors (old contexts, inefficient materials, and etc.), and above all, lack of engineering supervision in the present constructions of the city. Land uses facing earthquake hazards in Kermanshah include residential (about 16% located in the very high vulnerability range), road network (about 15% located in the very high vulnerability), and emergency operation, military and medical centers. This will definitely jeopardize any rescue operation in possible future earthquakes.
Earthquake and its related devastating mechanism constitute a very complex process in which various factors play a role. These factors can reduce destructive effects of earthquakes on urban settlements. High population density, patterns of spatial distribution, vast man-made environment and different characteristics and conditions of its constructions have made analyzing the situation if not impossible (without computer and advanced software), quite difficult. The present study has analyzed different indicators and sub-indicators, and introduced inappropriate status of physical elements, inefficient road network, overcrowded and worn-out urban fabric in the city center, high density, and inappropriate distribution of open and green spaces in the city as the key factors resulting in increased vulnerability of land uses in the current zoning of the city. Due to the close relationship between damages of an earthquake and proximity to earthquake fault lines, development of a physical-spatial model in Kermanshah metropolis before the occurrence of future earthquakes seems necessary. Results indicate that in case rules and principles of urban planning are followed, endogenous and horizontal development of the city toward southern and northwestern direction seem to be logical. Furthermore, considering factors such as slope, slope direction and the east-west direction of faults, development of the city toward west or east is not recommended unless principles of urban planning and reinforcing is completely followed. Rough and rugged topography of the northern and northeastern parts of the city is also another obstacle to the physical development of the city in these directions. Therefore, physical-spatial development in the southern and southwestern direction, along with infill and endogenous development according to the potential of the city are recommended