A Study On The Changes Of Vulnerability To Seismic Disaster Druing The Processes Of Urbanization

Earthquake disaster is the result of interaction between earthquake and hazard-affected objects in human & social system. For the same intensity of earthquake shock, vulnerability of hazard-affected objects can amplify or attenuate the impacts of the hazard. In recent years, study on vulnerability is recognized as the central and fundamental role to disaster research. On vulnerability to earthquake, different scholars have carried on a large amount of research from different aspects, but the present situation is in the majority. To have a deep understanding about the mechanism of natural disaster, not only the vulnerability of the current hazard-affected objects but also the changes and the driving forces need to be studied. With the system and overall concept, from dynamic perspective, this paper studies the characteristics of time-space changes of vulnerability to earthquake disaster, rules of the changes of earthquake disaster risks caused by changes of vulnerability in the process of urbanization. This paper constructed the methods for analyzing the vulnerabilities of hazard-affected objects in small scale human & social system and focuses on the changes of vulnerabilities to and loss risks from earthquake of building groups. The conception of functional vulnerabilities of life-lines had been defined and how to determine the vulnerabilities. Taking traffic system and water supply system as a case study, the paper analyzed the changes of functional vulnerabilities and risks of life-lines qualitatively. The conclusions of this thesis are summarized below.(1) High-resolution Remote Sensing-based method for determining structural vulnerability was constructed. The method includes three steps:①extraction of building attributes;②method validation and precision checking;③seismic vulnerability matrix optimization.①extraction of building attributes. The analysis of vulnerabilities and risk to earthquake depend on the type and area of buildings. The cast shadows in high-resolution remote images such as IKONOS or QuickBird can reflect three-dimensional attributes on spatial position and height of buildings. By the imaging theories of cast shadow, the height of building can be calculated based on the shadow length. The calculation formula is H = M×? . The H is the height of building, the M is the length of shadow and ? is the coefficient about image parameters. The structural types can be inferred from the information about height, spatial position and shape of building. With the outline of building roof the plan area can be obtained.②method validation and precision checking. 136 random samples of buildings are investigated to verify the reliability of the method. The results of statistical analysis indicate: (ⅰ)The type of building is closely related to the number of stories. All single-storey buildings are brick-made, 96.15% of the buildings with stories ranging from two to six are brick concrete ones, 97.44% of the buildings whose stories are seven or more are reinforced concrete ones. The type of buildings can be inferred according to building stories in the study area. (ⅱ)The relative height error of 93% sample buildings is less than 20%. (ⅲ)The relative area error of 95.8% sample buildings is less than 20%. The figures indicate that this method is feasible.③seismic vulnerability matrix optimization. By optimizing and combining the standard seismic vulnerability matrix in study area and the seismic vulnerability matrix in Wenchan earthquake, this thesis received the new matrix.(2) Utilizing the above method, the building structure type and total construction area of different types are extracted in 1995, 2002 and 2009. The changes of amount and constructional vulnerabilities and risk to earthquake of buildings are analyzed from 1976 to 2009. The main achievements can be concluded as:①From 1976 to 2009, the amount of buildings exposed to seismic hazard increased significantly, especially in Peri-urban zones. The building areas in 2009 are nine times in 1976. The growth of building areas in study area is not homogeneous. In different direction the growth rate of building area has preferential direction. The east and north is the main growth direction of buildings around Tangshan urban area, the south in Fengnan town, the east and south in Kaiping town. Guoyuan town and Fengnan town have the most number of buildings and the fastest growing rate. The total area of buildings of Guoyuan town in 2009 is 15 times more than the area in 1976. The total area of buildings of Fengnan town in 2009 is 12 times more than the area in 1976.②From 1976 to 2009, in the past 30 years, the structural vulnerabilities of buildings within the Peri-urban zones have been improved obviously. There is no raw-soil and timber structure building. The buildings with strong earthquake resistance such as reinforced concrete and brick concrete buildings increased rapidly, especially the reinforced buildings; compared to the strong earthquake resistance buildings, the less earthquake resistance buildings such as one-storey brick buildings reduced. It shows that from 1976 the anti-seismic capability of buildings has improved, and their structure vulnerability decreased in study area.③From 1976 to 2009, because of the growing of buildings, damage areas and economic losses have increased significantly, when different scenario intensity earthquake occurred in the study area. But the area ratio of damage buildings to all buildings reduced gradually owing to the growth of reinforced concrete and brick concrete buildings. The risks of damage areas and economic losses are different in different towns. The risk can be divided into four levels: highest, higher, lower and low. Compared among the nine towns, Guoyuan town has the highest risks; Fengnan town and Nvzhizhai town have the higher risk; Kaiping town has the lower risk; Zhengzhuangzi town, Yuehe town, Wali town, Dazhuangtuo town and Xijiatao town have the low risk. If the Tangshan earthquake occurs in 2009, the damage areas of buildings is six times more than the areas in 1976, and the economic losses is twenty-eight times.④This thesis concludes that there are three reasons for variations of the vulnerability to seismic disaster of buildings in Tangshan study area. They are growth of population and economy, adjustment of industrial structure and processes of urbanization. And the main force is the plan of the city in urbanization. It not only determines the amount and the quality of buildings, but also has the obvious directional traction.(3) This thesis defines the functional vulnerability of life-lines: functional vulnerability of life-line means that when this life-lines system is hit by a destructive earthquake, how much the possibility of function failure will be, what the size of dependent degree of the service objects will be, and the function recover ability after the destruction. The method based on event Tree-guided techniques for analyzing functional vulnerabilities of life-lines was constructed.(4)Based on the method, the functional vulnerability changes of traffic system in Yuehe town and water system in Xijiatao town are analyzed.①With the development of the traffic system in Yuehe town, the anti-seismic capabilities of roads and bridges have been improved obviously. When the traffic system is hit by an earthquake with low intensity (for example,Ⅵdegree), it will cause a small damage to the system. And it is good for earthquake relief and reconstruction, so the development of the traffic system can decrease the risk of earthquake disaster, when the intensity is low. When the traffic system is hit by a high intensity earthquake (for example the great 1976 Tangshan Earthquake), it will cause serious damage to the system. As transportation's socio-economic functions evolved and strengthened greatly, once the great 1976 Tangshan Earthquake should return, the transportation function failure risks would increase remarkably.②With the development of the water supply system in Xijiatao town, the structural vulnerabilities of the water pipes decreased. When an earthquake with low intensity occurs in this town, it will cause a small damage to the system and the water supply system is well or can be repaired quickly. It can help reduce the secondary disasters such as fire damage. So the development of the water system can decrease the risk of earthquake disaster, when the low intensity earthquake occurred. When the great 1976 Tangshan Earthquake return, the water system will be severely damaged. As the socio-economic functions of the water supply system evolved and strengthened greatly, once the great 1976 Tangshan Earthquake should return, the water supply function failure risks would increase remarkably.③Urbanization, development of businesses and transportation in Yuehe town are the main driving forces which caused the changes of the functional vulnerabilities of the traffic system; the driving forces caused the variations of the functional vulnerabilities of the water supply system are the fast development of the water supply system and production structure adjustment.(5)The results of the thesis have the practice guiding significance for making earthquake prevention and disaster relief planning and earthquake emergency preplan.