Urban planning has to perform seismic pathology of urban streets in seismic cities. Streets and roads are the most important spaces and urban elements in the cities which should be considered not only in space occupation and connecting spaces and urban activities but also in seismic vulnerability and on this basis it is planned to reduce environmental hazards and on top of earthquake-related. Many physical and functional characteristics of urban spaces and the distribution and concentration of the urban population take shape to comply with the location, capacity and function of the city streets network. Therefore, one of the most essential and the most important topics in the study of seismic cities is understanding of the relation between seismicity and urban streets through seismic vulnerability studies. This paper aims to assess factors and patterns of seismic vulnerability of urban networks with a prevention planning view in the 3rd district of Tabriz City.

This research has descriptive-analytic method and the statistical population is street network of 3rd district of Tabriz city. Data and layers of information have been prepared by documentary method and have been processed using the Delphi method and the method of ranking and rating IHWP in GIS. The main factors and indicators influencing streets vulnerability have been selected based on the eight indicators. These indicators include distance and proximity to faults, quality of buildings, the degree of closeness (width of the wall), building density, population density, the traffic service or traffic volume toward roads capacity, access to health centers and services and the land use system. The final map of seismic vulnerability has been produced by combining eight layers of information related to above mentioned indicatorsand based on it the seismic vulnerability levels and factors of the street network has been analyzed.

The final results of the seismic vulnerability of streets have been categorized in the 5 classes of vulnerability including very low, low, medium, high and very high. From total area 18.4% is estimated very low, 29.37% low, 31.77% medium, 14.21% high and 6.22% very high. Thus, taking into account the streets with medium, high and very high degree as vulnerable axes, it is concluded that 52.2% or more than half of the streets are seismic vulnerable and other half are relatively stable.

Within the vulnerable and unstable network, more than 20% of the streets are in high and very high vulnerable classes. Street network with high and very high vulnerability are mainly arterial streets with commercial and service land uses in the scale of trans-regional or secondary roads leading to artery of trans-regional which have high population density. These streets compose a high degree of closeness, increase in traffic service level, population density and land use system with the concentration of commercial, recreational and trans-regional land uses are the main causes of vulnerability. But, in the narrow streets (8 to 10 meters), the degree of closeness of arterial streets, traffic parameters and user system have increased the seismic vulnerability index. Spatial pattern of streets vulnerability has an increasing trend from East to West and from North to south. The results show Spatial intensity of vulnerable streets is located at the center of the district and on Vali Asr, Shariati, Aref and Razi Streets. Thus, the efficient and sustainable streets are located in the East of the under studied district.

The results also show that high vulnerable streets has less distance to fault and more distance from medical centers. In addition, they have high traffic and lower quality buildings and high risk land uses (electric and gas infrastructure) are located there. Since the wide streets are more often subject to less obstruction, this characteristic in seismic time cause to transfer the traffic of narrow passage to the main streets. Grid pattern of streets and frequency of intersections by slowing down the speed of the vehicle increase the volume of traffic and lead to an increase in seismic vulnerability.