تحلیل فضایی آسیب‌پذیری سکونتگاه‌های شهری و روستایی در برابر مخاطره زلزله مطالعه موردی: استان گیلان

The field of natural hazards research has a rich history in geography, appropriately so because it involves conflicts between physical processes and human systems. Natural events occur without direct human effect and endanger his social life. Events that enforce average annual up to 150000 human damages and more than 140 milliard dollars financial damages on counties and especially developing countries. Among all the natural disasters, the earthquake is one of the most serious ones. It brings tremendous economic losses and deaths of people, as well as the enormous effects on the harmonious and continuous development of society. Iran is an event ism country in the world. In this field look at the recent decades earthquakes statistics that reveal average once in every five years. Gilan province is located in south western of Caspian Sea in mountainous area of Talesh and central Alborz range that endure many earthquakes up today. The most ancient earthquake ever occurred in this area refers to Marlik civilization which is located near Rudbar – Rostam Abad. One of the recent earthquake in the 20th century in this area is Rudbar earthquake in 21 Jun 1990 with magnitude Ms = 7.7 Richter that caused many destruction. In one hand according to complex tectonic of central Alborz and in the other hand locating Gilan in the south west of Caspian sea that demonstrate many seismic activities, it illustrates as a result that this area is one of the active high potential seismic area of Iran. The current study is aimed at investigating the earthquake vulnerability of rural and urban settlements of Gilan province. To this end, Euclidean distant analysis and raster overlay have been conducted in GIS. To run the procedure, the first step is to calculate distance (pixels in 86 m dimension) between province and active and inactive fault line based on Euclidean analysis distance in Arc Map. The next step is aimed at standardizing the calculated distances using Raster Calculator Command. The, zoning of earthquake vulnerability of Gilan into five zones (based on active/inactive faults) is the primary goal. As a matter of fact, standardization leads to fuzzy maps. Standard score (distance) is calculated by dividing each score by sum of the scores. The next step tries to categorize zoning map and to translate Raster map into vector one in order to calculate the area of each risk category. Finally, overlay of urban and rural layers base on zoning map may help us analyze seismic hazard urban and rural regions of Gilan province. Results have shown that 40.72 % of total area of Gilan province are in 15 km distance from active fault. Also, 21.51 % of total area of Gilan province are in 15 to 30 km distance from active fault. Additionally, 64.45 % of total area of Gilan province are in less than 8 km distance from inactive fault (Table 1).   Table 1. Seismic hazard zonation according to faults Probability of earthquake hazard Distance to fault lines Relative area Active Faults Passive Faults Active Faults Passive Faults Very low risk 0-20 60-76 32-42 7.29 1.42 Low risk 20-40 45-60 24-32 13.82 3.96 Medium risk 40-60 30-45 16-24 16.66 8.13 High risk 60-80 15-30 8-16 21.51 22.04 Very high risk 80-100 0-15 0-8 40.72 64.45 sum - 100   According to seismic hazards due to active faults, 18 cities out of 51 urban regions are severely vulnerable to earthquake. Accordingly, 67.20 % of Gilan urban population are located at high-risk zone. Seismic hazard zoning map based on active faults have indicated that 20 cities are highly vulnerable to earthquake. (Table 2)   Table 2. Investigating the risk of earthquake in urban areas of Guilan province Probability of earthquake hazard urban Settlement Population (2011) Relative population frequency (percent) Active Faults Passive Faults Active Faults Passive Faults Active Faults Passive Faults Very low risk 0-20 3 1 135846 17106 1.14 9.07 Low risk 20-40 6 4 86133 144021 9.62 5.75 Medium risk 40-60 10 8 739095 754968 50.43 49.37 High risk 60-80 14 18 380908 273137 18.24 25.44 Very high risk 80-100 18 20 155188 307938 20.57 10.37 sum 51 1497170 100   Seismic studies on rural settlement of Gilan province have indicated that 1350 rural out of 2925 rural residences are severely vulnerable to earthquake because they are near to active faults. These regions are the habitat of 24.9 % of the total rural population. Zoning map based on inactive faults have shown that 1679 rural regions are vulnerable to earthquake (Table 3).   Table 3. Probability of earthquake hazard in rural settlements Probability of earthquake hazard Rural Settlement Population (2011) Relative population frequency (percent) Active Faults Passive Faults Active Faults Passive Faults Active Faults Passive Faults Very low risk 0-20 162 42 54240 30236 5.51 3.07 Low risk 20-40 379 147 183718 92018 18.68 9.35 Medium risk 40-60 481 291 255412 176183 25.96 17.91 High risk 60-80 553 766 245392 340448 24.95 34.61 Very high risk 80-100 1350 1679 244942 344819 24.90 35.05 sum 2925 983704 100   Studies have claimed that the majority of rural and urban regions of Gilan province are severely earthquake-prone. It is due to geographic and natural features of the mentioned province. To this end, some recommendations are given: Meticulous supervision on safety of building from the stage of plan-making to administration which have to be based on engineering principles for earthquake-prone cities including Baresar, Ataqur, Asalem, Haviq, and Roodbar which are next to active faults Prevention of formation of suburbs and towns on southern and northern parts of Gilan because these parts are really vulnerable to earthquake Prediction of temporary accommodation in central Gilan because this part is less vulnerable to earthquake To equip buildings, hospitals, schools, and other buildings located in big cities including Rasht, Bandar-E Anzali, Fuman, and Lahijan with facilities required in case of earthquake To hold training courses in rural and urban parts of the mentioned province to make residents prepared for earthquake and for emergency evacuation To prioritize reformation of old and historical buildings in Rasht because Rasht is mostly laden with old buildings which are really vulnerable to earthquake