Analysis Of Ground Motion Attenuation Relationship And Its Uncertainty In Chi-chi Aftershock

Strong ground motion is the major reason to destroy the structure of civil engineering in earthquake engineering. As the basis of earthquake prediction, engineering anti-earthquake and post-earthquake relief, ground motion attenuation relationship and its uncertainty have a significant influence on seismic hazard analysis. In recent years, to study the influence of main shock and aftershock sequence on structures becomes hot point. Only main earthquake is taken to consideration in the existing analysis of earthquake response and anti-earthquake design. Due to the effects of accumulated damages of structures, aft ershock is often the key factor caused collapse of constructions. The current study fruits mainly concentrate upon the main earthquake, but the study of aftershock is less, especially the aftershock sequence. For comprehensive consideration of the effects of aftershock on structures, it is necessary to design appropriately parameters of ground motion and study on the attenuation relationship of aftershock. Since earthquake sequence refers to a series of earthquake which occur in narrow room, their mechanisms may have some connection with each other or similar earthquake backgrounds. It is worthy for adequate consideration for the impacts of uncertainty of ground motion attenuation relationship in the same area and the same hypocentral region. There are in Taiwan Chi-Chi earthquake rich records of strong ground motion, among which the scale of earthquake sequence is astonishing, especially the number of aftershock sequence, promoting the study of the attenuation relation ship and uncertainty of aftershock.In this paper, a database is established based on the ground motion record of Chi-Chi aftershock of Taiwan, the random effect method is used for the statistical regression of ground motion attenuation relationship of the database, the ground motion features of Taiwan and the influences of different factors on the ground motion are obtained by the analysis of attenuation result and decomposition of error, so as to provide reference and basis for reduction of the uncertainty of ground motion attenuation relationship model more reasonably. The contents and conclusions of the research are as follows:(1) By acquiring the hypocenter information and site data of stations, the ground motion database of Chi-Chi aftershock of Taiwan is established and the basic features of the ground motion of Taiwan are analyzed. Considering CB08 model in NGA program, it is found in the study of applicability from propagation path, hypocenter features and response spectrum that the existing regression results of CB08 model are higher compared with the ground motion record of Chi-Chi aftershock, which cannot reasonably reflect the unique geologic structure of Taiwan and the directivity effect of wave propagation path.(2) Using the ground motion data of Chi-Chi aftershock of Taiwan, the ground motion attenuation relationship is established by random effect method and the regression results are analyzed and compared. Generally, the results of the research provide certain reference to the small and moderate earthquakes, but the result is smaller for large earthquakes.(3) Applying the regression results of ground motion to the seismic hazard analysis and using uncertainty correction, it is found the ground motion exceedance probability curve changes greatly before and after correction and the exceedance probability is improved significantly after correction, especially embodied in the low probability stage.(4) The ground motion data of single site and single path of Chi-Chi aftershock sequence are used for the uncertainty study of attenuation relationship, the model error is of systematical decomposition and quantitative analysis according to the different ground motion influencing factors and the research results are compared with other results. By reducing the error items, the uncertainty of the model can be reduced significantly.