تحلیل فضایی خوشه‌های آسیب‌پذیر بافت کالبدی شهر گرگان در برابر زلزله (با استفاده از آمار فضایی )

نوع مقاله : مقاله علمی پژوهشی

نویسندگان

1 دانشیار جغرافیا و برنامه ‏ریزی شهری دانشگاه اصفهان

2 دانشجوی دکتری جغرافیا و برنامه‏ ریزی شهری، دانشگاه اصفهان

چکیده

زلزله یکی از خطرناک‏ترین، مخرب‏ترین، و غیرقابل پیش‏بینی‏ترین مخاطرات طبیعی شهری به‏شمار می‏آید. طبق اعلام سازمان مدیریت بحران کشور، 78درصداز مساحت کشور در محدودة خطر لرزه‏خیزی بالا قرار دارد و 10درصداز تلفات انسانی ناشی از بلایا در نتیجة زلزله است. استان گلستان جزو استان‏های رده دوم خطر زلزله و در ردة خود اولین استان پُرخطر است. بر همین اساس، هدف از پژوهش حاضر سنجش و تحلیل مکانی خوشه‏های آسیب‏پذیر بافت کالبدی شهر گرگان در شرایط بحرانی به‏منظور تعیین نقاط نیازمند مداخلة فوری است. پژوهش حاضر از نوع کاربردی و روش بررسی آن توصیفی-تحلیلی است. جامعه آماری شامل مرزهای جغرافیایی شهر گرگان براساس سرشماری سال 1395 است. برای تعیین پهنه‏های آسیب‏پذیر از مدل‏هایی نظیر ANP و VIKOR استفاده شده است. برای تحلیل فضایی خوشه‏های آسیب‏پذیر بافت کالبدی نیز از آمارة فضایی Getis-Ord بهره گرفته شده است. یافته‏های پژوهش نشان‏دهندة آن است که شاخص مصالح ساختمانی با وزن 452/0 و شاخص ریزدانگی (مساحت قطعات) با وزن 126/0‏ به ترتیب بیشترین و کمترین تأثیرگذاری را در ارزیابی آسیب‏پذیری بلوک‏های شهر گرگان دارند. همچنین، بیشترین میزان آسیب‏پذیری از لحاظ کالبدی مربوط به مناطق مرکزی و جنوبی و حاشیه‏های شرقی و تا حدودی غربی شهر گرگان است. تحلیل Hotspot به طور واضح شکاف بین مرکز و جنوب را با سایر مناطق شهر گرگان نشان می‏دهد. درواقع، پهنه‏های آسیب‏پذیر شهر گرگان عمدتاً بر بافت‏های تاریخی و مناطق حاشیه‏نشین منطبق است.

کلیدواژه‌ها

موضوعات


عنوان مقاله [English]

Spatial Analysis of Vulnerability Clusters in Physical Texture of Gorgan City against Earthquake, Using Spatial Statistics

نویسندگان [English]

  • Ali Zangiabadi 1
  • Abdorreza Dadbood 2
1 Associate Professor, Faculty of Geography and Planning, University of Isfahan
2 Ph.D. Student of Geography and Urban Planning, University of Isfahan, Isfahan, Iran
چکیده [English]

Introduction
Earthquake is one of the most natural hazards for cities, being dangerous, destructive, and unpredictable. According to Iranian Crisis Management Organization, seventy eight percent of the country's surface is in high seismic risk area, with 10% of human-caused mortality related to earthquakes. Golestan Province, the second-ranked province in this regard, always faces earthquake hazard, located in the first high-risk areas. In general, four main theories are related to cities’ vulnerability: first, the human ecology theory that has emphasized the unbreakable bonding of biophysical processes and social processes; second, the theory of political economy, which has integrated macro and micro perspectives, providing a better analytical framework for complexity and dependence comprehensive understanding of vulnerability-causing factors; third, the theory of community-oriented compatibility, which is based on identification, assistance, and implementation of community-based activities strengthening the capacity of local people to adapt to life in a risky and unpredictable situation; and fourth, resilience which is the capacity or ability of the community to predict, prepare, and respond quickly against the effects and consequences of disaster. According to the country's Crisis Management Organization, 78% of the country lie in high-risk seismic areas with 10% of human losses coming from earthquake-related disasters. Golestan Province belongs to second-ranked provinces facing earthquakes in Iran, being first in terms of the high risk from such disasters. Results from several surveys show that 840 earthquakes have been registered in Golestanwith many regions of the province susceptible to landslides. Seismic zoning maps has shown that Golestan Province has four zones, regardless of the effect of alluvial deposits. They include areas with very high, high, medium, and low seismic hazard. Gorgan, the capital city of this province is located in very very high and high areas. Accordingly, this research tries to measure and make a spatial analysis of vulnerability clusters in physical textures of Gorgan in critical conditions in order to determine immediate intervention. However, seismic zoning maps for seismic rock placement, based on the background of accelerated shifts of earth's powerful movement for the return period of 475 and 2475 years show that regardless of the effect of alluvial deposits Golestan Province has four zones, areas with high, high, medium and the city of Gorgan is low in many areas.
Methodology
The current research was an applied one, its method being descriptive-analytical. It investigated the determinant criterion of physical texture vulnerabilitydegree in Gorgan in terms of five criteria, namely number of floors, fineness, buildings’ age, and therir materials. Once this criterion got evaluating and converted to comparable and standard scales, it was used from Analytic Network Analysis (ANP) to determine relative weight of each criterion. Indicator prioritization was done according to expert opinions and indicators’ evaluation. Finally, the blocks were classifiedwith VIKOR Model in terms of their vulnerability, resulting in the physical vulnerability map of building units at the urban blockslevel of Gorgan city. Then, vulnerable spatial clusters analysis of Gorgan city was carried out via the Getis-Ord model.
Results and Discussion
Results from the study show that the highest and lowest effective factors for vulnerability assessment of the Gorgan city blocks were related to the index of building materials with a weight of 0.425, and the index of pettiness with a weight of 0.126, respectively. Based on VIKOR Model results, the highest degree of physical vulnerability could be seen in the central and somewhat southern parts of Gorgan. Also, the eastern and western regions and somewhat north of the city fared better with regard to this index. The Hotspot analysis clearly showed the gap between the center, the south, and the margins of the eastern and western regions with other parts of Gorgan. As a result, the central and southern regions as well as the margins of the eastern and western regions of Gorgan were in an inappropriate situation in terms of vulnerability during the earthquake. At the same time, the northern, western, and eastern parts of the city suffered less damage during the earthquake, thanks to their buildings’ physical characteristics.
Conclusion
Researches like Ródenas et al. (2018), Rusydi et al. (2017), Ianoș et al. (2017), Kushe et al. (2017), Mehraban Motlagh and Motamedi (2018), and Paivastehgar et al. (2017) have emphasized zoning of vulnerable sites in cities such as Palu, Bucharest, Karonga, Shiraz, and Imamzadeh Hasan, Tehran. However, the present study  focused on spatial analysis of the vulnerable zones of Gorgan, simultaneously determining their clusters. At the same time, this research did not overlook focusing on vulnerability zoning as well. The comparative analysis of vulnerability in Gorgan indicated that the central region had less residential units than the peripheral region of Gorgan. Buildings in the central part were more ancient. The periphery buildings had higher elevation than the center. Also, peripheral buildings were better in terms of access to passages, being wider than the central parts of the city. In general, the buildings in the peripheral parts proved to be less vulnerable than the central ones. In this regard, it is suggested to 1) establish crisis management centers and emergency services in the west and east of the city, 2) prevent congestion especially in hazardous areas, 3) open roads, and 4) give incentives to worn-out buildings regeneration by both the government and the municipality.
Through comparative analysis of vulnerability in Gorgan, it can be concluded that the central area has less residential units than the periphery of the city. Older buildings are more in the central part, while those in the periphery have higher elevation. Also, peripheral buildings are better off in terms of access to passages.

کلیدواژه‌ها [English]

  • Vulnerability
  • Vulnerable clusters
  • earthquake
  • Physical texture
  • Gorgan City
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