The Study of Efficiency of Street Networks in Earthquake (Case Study of Zones 1 and 5 of Tabriz Detailed Pland)

Large earthquakes usually cause huge damages to human life. Street network vulnerability makes the rescue operation to encounter serious difficulties especially at the first 72 hours after the incident. Today, physical expansion and high density of great cities, due to no attention to hierarchical street network, narrow access roads, large distance from medical care centers and location at areas with high seismic risk, would lead to a perilous and unpredictable situation in case of the earthquake. Occurrence of earthquakes with large magnitude would destroy the functionality of street networks and cause large amount of casualties and major financial damages. In Tabriz city, the areas of first and fifth zones are equal to 3327 hectares. The area of first and fifth zones is over 2844 and 483 ha respectively. According to current estimates, the population of these zones is equal to over 458939 people. In this research using 12 indexes such as: land use, width of roads, height of buildings, street inclusion, population and construction density, buildings area, quality, materials and antiquity of building, access to medical centers, distance and proximity to major faults vulnerability degree of street networks in zones 1 and 5 of detailed plan of Tabriz against the earthquake is calculated through overlaying maps and data in combination with IHWP method and GIS. The article concludes that buildings alongside the streets with high population and building density, low building quality, far to rescue centers and high level of inclusion represent high rate of vulnerability, compared with other buildings. Also highways and streets with substantial width and low building and population density hold little values of vulnerability. By moving on from east to west of the zones, the vulnerability increases. This vulnerability of streets is in high level in the central zones. Therefore, the existing street networks in the center will be unable to perform their role at the case of occurrence of earthquake.