An Assessment of Safe Boundary in Urban Area in Relation with Seismic Vulnerability Case Study: Cities of Yazd province

Irregular expansion of cities without considering the faults locations and directions, increases the possibility of placing cities on seismic zones, which in case of earthquake occurance, creates great financial and human damages. Therefore, specifying the safe boundary in urban areas and its observation canbe effective in reducing earthquake damages.Creating the facilities and services including fire station, police station and therapeutic and sanitation centers become more difficult, costly and time consuming by physical spread of the cities. This paper is an applied research which with respect to the cities and faults locations, aimed to determine safe boundary of the cities in relation with seismic vulnerability. The under  study area is Yazd cities. Firstly the geology and seismic situation and then the population and urbanization features have been studied.
Finally using two different methods namely, A) using available standards (faults safe boundrary with minimum and maximum standard range300-1000 m) B) Using data of the last 100 years regarding the  location of cities and radius distance from probable earthquakes, the safe urban boundary has been determined.
Research findings show that: the main part of Yazd province is located in areas that are at low and medium risk of earthquake. The southern, eastern and north-eastern cities are at high risk of earthquake. In Nedoshan, Harat, Marvast, Taft, Bahabad, Deyhouk and Eshghabad, appointment of urban safe boundraty should be taken into more consideration. According to urbanization study 21.74 percent of cities and 7.63 percent of population in Yazd province are located  at areas with high risk of earhquake .Population forecast show that urban centeralization in Yazd province is increasing. Therefore vulnarabal population will increase. With regard to distance radius from faults and  probable earthquakes and with respect to  historical earthquakes, the whole of Yazd cities are located  at proper radius, but this does not mean that the province cities are secure against earthquake,  because the first method(available standards), proofed its contrary. Also this study showed that relying only on the earthquake historical data (seismici data of the last 100 years) does not surely secure the safety of cities against earthquake.