Forecasting Near-fault Ground Motion Field Of Changchun City

Earthquake is one of tremendous nature disasters, the human beings must face. For thousands of years, devastating earthquake has brought so much adversity and suffering. In the 20th century the number of people who died in earthquake has reached 1,500,000. Our country is one of the countries, have fearful earthquake. In human history, the number of earthquake, which killed more than 200,000 people, is six. Four of them have happened in China. From 1940 to 2000, the People killed in every kinds of nature disaster have reached the number 550,000, 280,000 of them dead in earthquake disaster, more than a half. In statistical, more than 90% of earthquakes are tectonic earthquake. Fault existing is the basic condition of the tectonic earthquake occurring. Fault is a common phenomenon of geological structure. It breaks the continuity and integrity of geological bodies. At the early time, people found the potential contacting between earthquake and fault. After the theory"Elastic Rebound"(Reid, 1910), was presented, people considered earthquake as a phenomenon of lithosphere motion. The motions of fault rock, which caused by outside forces, are considered as the physical essence of tectonic earthquake. People want to find the answers of two problems when they use the Earthquake Engineering attitude to research fault. One is whether the fault will cause the ground rupture, and when earthquake break out. If ground ruptures, how much is the displacement. Another one is how the fault belt and near fault ground motion field distribution. Changchun locates on an area, which has a low activity of fault, so the probability of ground break caused by fault is little. People care about the second problem, the distribution of near-fault ground motion field. The second problem is one of hotpot in researching of Earthquake Engineering. As people have more and more knowledge of earthquake disaster, near-fault ground motion field is considered more and more important. That is because near-fault ground motion field distribution is an important crucial factor of seismic motion inputting and determining the range of avoiding belt. So the researching of city fault and forecasting of near-fault ground motion field have significant theoretically and practical meaning. The paper combines some parts of China Seismic Bureau"10th 5years scheme"item,"Fault exploring and seismic hazard risk assessment of Changchun". It also researched some crucial problems, such as fault exploring, activity study, seismic hazard risk assessment and forecasting of near-fault ground motion field when given earthquake occurring on Jianshanzi-Kalun fault. In this paper, the author has finished these jobs as follow:1) The paper introduced the history and actuality of city fault research particularly. This includes fault exploring, activity age survey, seismic hazard risk assessment and forecasting near-fault ground motion field. Then the author discussed the existing problems of all the researches and methods. He also did some researches in defining and character of near-fault ground motion, and has some useful conclusion. This part is helpful to understand the method and process of forecasting near-fault ground motion field.2) Based on the view of Earthquake Engineering, the paper summarized and analyzed some data and material systemically and comprehensively for the first time, such as geological structure, neo-tectonic movement, activity of fault, et al. Then the paper concludes general evaluations about the background of seismic structure and the condition of earthquake occurring. This part is significant and helpful to comprehend the structure movement intension and seismic activity in this area.3) The author used some different ways, such as electronic method, shallow seismic exploration, ground penetrating radar and united boring section, to explore one fault, comprehensively and systemically. He finds out the fault parameters such as location, orientation and the depth of up-break point. Based on the result of exploration, this paper gets a scientific conclusion about the activity of 4 faults of Changchun city. Kaiyuanpu-Xiaochengzi fault just cuts the Cretaceous, does not cut the middle Pleistocene, so we consider it is a pre- Quaternary fault. Jianshanzi-Kalun fault, Nanhu-Shangjiawopu fault and Yitonghe fault cut through the Cretaceous, and disturb the weathered crust, and create some scarps. So can't eliminate the possibility of these faults have active in early Quaternary. Aim to the safety, we consider these 3 faults are early Quaternary fault. This part has accumulated abundant of data about fault exploring and activity study in buried region. It has practical meaning.4) The paper assessed the aimed fault seismic hazard risk. The paper concludes that the maximal potential earthquake of Changchun region is Ms 6.0, by the repeat rule of historical earthquake and the similarity rule of seismogenic structure. We acquired the seismic moment and the magnitude upper limited of potential earthquake of aimed fault, by experiential formula. As we know that Changchun has little record of earthquake and it's fault is inactive, correspondingly. We choose Poisson model to research the future seismic risk of aimed fault. According to the research result, the Jianshanzi-Kalun fault is the most dangerous one of aimed fault in Changchun city. In this part, the paper advanced a new method of seismic risk assessment, which will be used in estimate of early Quaternary fault. The new method is a reference for the region where fault is not distinct active.5) The paper combined two methods, 3-D finite element analysis and parallel computing, to calculate the ground motion of Jianshanzi-Kalun fault. We gathered 1518 bore data and arranged 19 shallow seismic exploration profiles to established the underground structure 3-D model, which concludes many parameters such as location, shear wave velocity, poisson ratio, density, et al. We acquired the source parameter and established the source model by experiential formula. We calculate the 3-D long-period ground motion by 3-D finite element analysis. We invert low-frequency ground motion by 1-D underground medium model. We compose the high- frequency and low-frequency ground motion to broad- frequency ground motion. We acquired near-fault ground motion time-history by calculating 1-D soil non-linear seismic response. We forecast the near-fault ground motion field and acquire the seismic spectrum, by ground motion time-history. This part not only can help us to further know near-fault ground motion, but also is impending needed by engineering aseismatic design. The paper consults some part of China Seismic Bureau"10th 5years scheme"item,"Fault exploring and seismic hazard risk assessment of Changchun". Some conclusions in this paper have evaluated by expert group of China Seismic Bureau. The major ones have been adopted by the engineering report. In the coming years, fault exploration is not only an engineering mission, but also a researching work, about engineering aseismatic in city. This job is more useful to alleviate the seismic hazard in city. The result of this paper can used to guide the city layout, aseismatic layout, land use and the site choose of important engineering of Changchun city.The paper points out some problems in researching and gives some advise for the further research. As we should know, the methods of calculating and forecasting ground motion are not perfect. Some of them are tentative. As the researching in this field progress, this result, forecasting near-fault ground motion field, will be considered, more and more valuable. As my knowledge is limited, there are maybe some faults and mistakes in the paper. Hope you to correct me when you find one.