Two Improvements In Urban Earthquake Risk Assessment And Risk Management

Urbanization is a sign of expeditious progress in the human society with characters such as high population, prosperous business, dense buildings, convenient transportation systems and perfect infrastructures. During some destructive earthquakes occurred in or near cities in recent years, it is revealed that the vulnerability in urban areas increases with the quick steps of urbanization. The vulnerability there depends not only on the potential direct damage such as damages of engineering structures and infrastructures, losses of property and the death or injury of victims, but also on the potential indirect damage such as interruption of business, reduction of output, induced fires and emotional stress on victim families. Urban Earthquake disaster management has been the emphasis of the prevention and mitigation of earthquake disaster, its content is more abundant and methods are more complex than before, and its measures are updated time after time. It must be more and more prominent that the application of financial instruments to the prevention and mitigation of earthquake disaster, while the management system is moving from planned pattern to market pattern after China entered WTO. In this paper, two key strategies in earthquake risk assessment and risk management for urban areas are studied. One is ground motion based vulnerability evaluation method for buildings which needs to be solved urgently in earthquake risk assessment in China. The other one is financial instruments, such as insurance, reinsurance and catastrophe bonds (cat bonds in brief), combined with engineering earthquake risk evaluation which must be faced in earthquake risk management after China entered WTO.This paper consists two main parts which are related with each other in general sense and independent in details. In the first part, the characteristics of seismic hazard in urban areas and the development trend of the earthquake risk assessment and risk management in China and abroad are summarized, and the purpose and the content of this paper are expounded. The evolution and the state of the art of vulnerability evaluation are reviewed, the existing problems in this field in China are pointed out, and the urgent requirement to develop a ground motion based vulnerability evaluation method combined with domestic earthquake damage experience is emphasized. The vulnerability evaluation procedure of HAZUS99 which is widely adopted in the United States and world wide is introduced in briefly. Then the general technical frame of the first part is illuminated as follows:by means of the form of HAZUS99, the earthquake action is expressed by demand spectra and the capacity of buildings is described by capacity curve. The probability of being or exceeding a given damage state of buildings by a given ground motion intensity is calculated from the spectral displacement corresponding to the intersecting point of the demand spectrum and the capacity curve, the median value of spectral displacement at which the building reaches the threshold of the damage state and the standard deviation of natural logarithm of spectral displacement of the damage state. Finally, a set of fragility curves are constructed for 5 damage states. To combine it with the virtue of valuable earthquake damage experience accumulated in China and stored in damage matrix, an inversion strategy is designed to search seven ratios of 4 spectral displacements of buildings to the median values of spectral displacements of 4 damage states by the criteria of the convergence of the values of the standard deviations of the natural logarithm of the spectral displacements of four damage states as the objective function, a hybrid procedure integrated the Simplex with the Generic Algorithm is adopted and the program is updated for this purpose from an existing one. To illustrate and validate the method developed in this paper, 4 spectral displacements of buildings corresponding to 4 intensities, 4 median values and 4 standard deviations of natural logarithm of spectral displacements...