A Study On Rapid Assessment Of Post-Earthquake Transportation Systems In Urban Agglomeration

In recent years with the rapid development of the economy and urbanization in ourcountry, a new pattern of spatial organization, urban agglomeration has appeared. Untilnow there are twelve urban agglomerations and their embryos. In these urbanagglomerations distances between cities are very small, economic relations are very close,the population density is very high, the social fortune of the unit area is much larger thanthe national average and their life systems have close interrelations. It's proved thatearthquake disasters in the urban agglomeration are more serious and they bring largereconomic loss than that in a single city. Now the existing twelve urban agglomerations andtheir embryos are most located in the 7 or 8 degree zone on the third generation map ofseismic intensity regional zonation. According to historical strong earthquake catalogs,there are many major earthquakes (Ms≥5.0) occurred within or around the urbanagglomeration areas except for the urban agglomeration in the middle Hunan province,where only one such shock happened. There are seven urban agglomeration regions withMs>7.0 earthquakes. Owing to the special characteristics of earthquake disasters inurban-agglomeration regions, the rapid development of urban agglomerations in ourcountry and their serious seismic risk, the problem of the earthquake disaster migration inthese regions must be faced and recognized. In this paper, firstly, the concept, the evolvement and the developing trend of the urbanagglomeration and the seismic risk of the urban agglomeration regions in our country arepresented, earthquake disasters happened in the urban agglomerations are summarized andthen the seismic hazard characteristics are discussed. It's suggested that the devastation oftransportation systems is the main characteristic of earthquake disasters in urbanagglomeration regions. So the chief object of this paper is to develop the rapid assessmentmethodology for the performance of the post-earthquake highway transportation networkin urban agglomeration areas in our country. The system performance measure, arealdistance-based accessibility (measure Ds), proposed by Nobuoto and Nojima is introducedin this paper. But it is not proper for the highway transportation systems in our urbanagglomerations, so measure Ds is modified. Finally the modified measure Ds is applied tothe urban agglomerations highway system in the Pearl River Delta as a case study.The results of this paper are as follows:Through analyzing earthquake disasters happened in urban agglomerations ormetropolitans, it is concluded that the hazards in these regions have the followingcharacteristics. (1) In urban agglomeration earthquakes will bring immense economiclosses and social influence. (2)When urban agglomerations are hit by a destructiveearthquake, there will be many cities exposed to disasters. However, the disaster extentsare different for cities in this region and disasters have interrelations. (3) Lifeline systemsare of most seismic frangibility and disasters in transportation systems are more serious.A traffic system is the framework to link cities in an urban agglomeration region. Itbreaks old regional division, so the economic development of the cities in an urbanagglomeration region is more harmonious. Hence the development of the urbanagglomeration region greatly depends on the traffic system. If the traffic system isdestroyed by an earthquake, not only becomes the region weaken or regional economicfunction is lost and immense economic loss and social impact are caused, but also greatdifficulties are brought to earthquake disaster fighting, evacuation of victims and regionaldispatch of succors and emergent materials.Earthquake disasters occurred in urban agglomeration regions indicate that trafficsystem devastation is the main portion of the earthquake hazards in urban agglomerationregions. It brings great impact on the short and long-term economic development. However,the transportation system plays an important role during the post-earthquake emergentrelief. So it is very necessary to develop an assessment method for intercity traffic systemperformance in urban agglomeration. This work proposes a performance assessmentmethod, measure Ds for post-earthquake traffic system suitable to urban agglomerationregions in our country. The methodological approach emphasizes simple measures thatrequire only available data on network configuration, damage, and pre-disasterorigin/destination traffic. This measure can be used to evaluate the intercity accessibility ofall cities in an urban agglomeration region in each period of post-earthquake systemdeterioration and then the spatial disparity of the accessibility in the region is demonstratedwhich is useful for the rapid intercity emergency. This measure can make quantitativeanalysis to the change of the performance restoration of each city over the course of thereconstruction period. By the application of the measure Ds to the Pearl River Deltaurban agglomeration, it is found that the value of Ds depends not only the deteriorationextent of the highway system, but also the restoration process of the system and thecharacteristics of regional road network etc. And the intercity accessibility doesn't go upsimply following the time increasing and has spatial and time disparity. The value ofDs even depends on specifical roads which are repaired and the importance of these roadsto the highway system of these cities. So from another point of view by using measureDs the incidence of the road to the improvement of the accessibility of the city can beestimated, the seismic retrofit of individual highways is prioritized after the disaster andeffective rebuilt plans are designed according the assessment result.