Physical Vulnerability Assessment of Urban Fabrics against Earthquake by RADIUS Method (Case study: Shiraz City, 3rd Municipal District)

1. Introduction
Iran is being crossed by several major fault lines that cover at least 90% of the country and it is a seismic prone region. The country has been host to a long series of devastating earthquakes that have resulted in heavy casualties and damages. Due to the geographic location of Iran (located on an earthquake belt of Alps- Himalaya) many natural disasters occur annually. The Iranian plateau is subject to most types of tectonic activity, including active folding, faulting, and volcanic eruptions. It is well known for its long history of disastrous earthquake activity. During the last several centuries various regions in the country have experienced destructive earthquakes. Not only these earthquakes have killed thousands, but they have also led to waste of valuable natural resources. Since 1900, at least 126,000 fatalities have been resulted from earthquakes in Iran. The expansive infrastructures, along with the high population density make cities highly vulnerable to the severe impacts of natural incidents. So, the need for evaluating and visualizing the vulnerability of urban areas becomes a necessity.
Shiraz, which is one of the biggest urban areas, is located in the south part of Iran. This city is more than 4000 years old. Shiraz lies in Fars Province, a central area for Persian civilization. Due to exposure to several active faults in and around the city the greatest risk is the risk of earthquakes. The major faults in Shiraz region and its vicinity are Sabzposhan, Kohenjan, Sarvestan and Karehbas. The 1824 earthquake had destroyed parts of the town. The 1860 and 1890 earthquakes had ruined historical buildings of this city; Shiraz was renewed and flourished again. In 1972 there was an earthquake with Magnitude of 6.9 in Ghir and Karzin with a lot of people killed and injured. There were again huge earthquake in Fars Province recently (3 years ago in Lamerd and 2 years ago in Shiraz) in the area. The last advices from Persia state that a severe earthquake has leveled Shiraz with the ground, and 15,000 persons perished in the ruins. So, the study aims to: a) identify vulnerabilities in the 3rd municipal district of Shiraz and the amount of physical damage can be caused by an earthquake with a magnitude of 7.4: b) determine the extent of casualties caused by the earthquake.
 
2. Materials and Methods
In order to reduce the vulnerability of Shiraz, before any planning and decision-making, it is necessary to analyze the earthquake damages based on its different conditions before its occurrence for obtaining a clear vision of probable earthquake happening and its potential consequences on the basis of simulating probable earthquake and by vulnerability maps. First step is to identify the vulnerability of urban elements with using existing models and methods. Considering the importance of urban earthquake vulnerability assessment issues in urban planning, this paper estimates the vulnerability of 3rd municipal district of Shiraz by using RADIUS method with a cell size of 1×1 km. This tool is based on three aspects: Seismicity of the area, soil conditions and structural characteristics of the buildings. By using the results of analyses in a scenario based vulnerability evaluation procedure, the priority level of various parts of the district for implementation of preventing measures are obtained. The results are presented in terms of maps of vulnerable places.
 
3. Results and Discussion
Analyses show that this district and the buildings located in this area is highly vulnerable against earthquake. If an earthquake occurs with 7.4 magnitude, over one third of the buildings will be destroyed and about 3,700 people will be died and at least 30,508 people will be injured.
In the district, development of the city is not in an orderly and planned way and people have built their houses without following the current regulatory framework that ensures good structural behavior during the occurrence of a severe earthquake. This study shows that the existing organic fabrics, irregular communicational networks and lack of proper urban equipments, make this part of the city vulnerable against earthquake.
Absence of disaster management institutions at local and central levels, lack of earthquake mitigation plan and urban development-related legislation besides low level of community preparedness and public awareness have not only intensified the rate of conversion of the city into a hazardous zone but have also resulted in loss of the opportunities to build safer community in newly developed areas. Thus, the results of these evaluations can be used to figure out the management and urban programs needed to reduce injuries and fatalities.
           
4. Conclusion
Many models are presented to analyze and evaluate the seismic vulnerability of cities; and various researches have been done. In those works conducted inside the country the investigated area was not small. Flexibility of the proposed analytical model makes it usable for urban settings, without any limitation. Therefore, in this issue it is better to use RADIUS models, because the applied models should be compatible with the study area conditions. RADIUS model have the advantages. Within the use of this viewpoint to codify earthquake scenarios and estimate probable damages it is possible to have the best perceptions about earthquake and the meter of risks that we are facing with. Furthermore, damage amplitude and the susceptible area in city will be determined. However, this has some defects. Lattice in the RADIUS software is stable and done as an equal square. Creation wrongs are the bound and appropriate Un lattice in the studied area and always this part of information in the borders of area not enter correctly to the software. In the whole RADIUS model due to rapid represention of result in the short period of time, for the area that the exact and complete information is not available it is a suitable model for estimating damages of earthquake.For the current condition in most of the Iranwhere don’t have GIS information it can be a good model for estimation of earthquake damages.