تحليل فضايي آسيب پذيري سكونتگاه هاي شهري و روستايي در برابر مخاطره زلزله؛ مطالعه موردي: استان گيلان

Spatial analysis of vulnerability in urban and rural settlements against earthquake hazard Case Study: Guilan Province

پژوهش در زمينه مخاطرات طبيعي داراي سابقه اي غني در علم جغرافيا است. در ميان تمام مخاطرات طبيعي، زلزله يكي از جدي ترين آن ها است كه زيان هاي عظيم اقتصادي و مرگ ومير مردم را به بار مي آورد. كشور ايران بر روي كمربند زلزله خيز آلپ ـ هيماليا واقع شده كه يك منطقه مستعد زلزله است. از اين رو زمين لرزه هاي مخرب عظيمي در گذشته در كشور ايران روي داده است. هدف اصلي از انجام اين پژوهش تحليل فضايي ميزان خطر زلزله در سكونتگاه هاي شهري و روستايي استان گيلان است. در اين راستا از تحليل هاي فضايي در نرم افزار ArcGIS و تحليل فاصله اقليدسي استفاده شد. احتمال وقوع خطر زلزله در استان گيلان بر اساس فاصله از خطوط گسل هاي فعال و غير فعال تحليل شد. نتايج نشان داد كه40/72 درصد از مساحت استان گيلان در فاصله صفر تا 15 كيلومتري گسل هاي فعال قرار دارد و همچنين 45/64 درصد از مساحت اين استان در فاصله اي كمتر از هشت كيلومتر تا گسل هاي غير فعال قرار دارند. تحليل خطر زلزله در نقاط شهري استان گيلان براساس خطوط گسل فعال حاكي از آن است كه 18 نقطه شهري در پهنه با خطر بسيار بالاي زلزله و 14 شهر در پهنه با خطر بالاي زلزله قرار دارند. براساس مطالعات انجام شده 20/57 درصد از جمعيت نقاط شهري در پهنه با خطر بالاي بسيار بالاي زلزله (80 تا 100 درصد) ساكن هستند. تحليل خطر وقوع زلزله در نقاط شهري استان گيلان براساس گسل هاي غير فعال حاكي از آن است كه، 20 نقطه شهري با جمعيت نسبي 25/44 درصد در پهنه با خطر بسيار بالاي زلزله ساكن هستند. مطالعات انجام شده در زمينه نقاط روستايي استان يلان براساس گسل هاي فعال نشان داد كه از مجموع 2925 سكونتگاه روستايي، 1350 روستا با جمعيت نسبي 24/90 درصد در پهنه با خطر بسيار بالاي زلزله ساكن هستند. تحليل خطر زلزله در نقاط روستايي استان گيلان براساس فاصله از گسل هاي غيرفعال نشان داد كه 1679 روستا در پهنه با خطر بسيار بالاي زلزله قرار دارند. در پايان پژوهش پيشنهاد هايي در راستاي مقابله با خطر وقوع زلزله ارائه شد.

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). 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) 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). 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:1.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 2.Prevention of formation of suburbs and towns on southern and northern parts of Gilan because these parts are really vulnerable to earthquake 3.Prediction of temporary accommodation in central Gilan because this part is less vulnerable to earthquake 4.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 5.To hold training courses in rural and urban parts of the mentioned province to make residents prepared for earthquake and for emergency evacuation 6.To prioritize reformation of old and historical buildings in Rasht because Rasht is mostly laden with old buildings which are really vulnerable to earthquake.