| Site condition governed distribution of strong ground motion and earthquake damage significantly. The studies on this issue have been important in the areas of engineering seismology and seismology for decades. Many problems on ground motion are associated with in the lack of site condition information of the observation stations. To detect3D subsurface Vs structure of engineering site by observing microtremors, must be a powerful tool for development in this subject of Earthquake Disaster and Seismic. In this thesis, the exploration and imaging of the3D subsurface Vs structure by means of microtremors approaches are studied. The main achievements are summarized as follow. The general characteristics of site microtremors spectrum and distributed regularity are studied based on a large number of site tests and analyses in city district. The data indicate that the thickness of cover layer and soil stratification will influence microtremors spectrum and distributed regularity directly. The foundation soil layer could be regarded as a system, waves transmitted from different seismic origin travel in this system, then, the response will be different as the soil foundation structure changed. So in different areas, analyzing of the characteristics of the microtremors spectrum, certainly get a different result. This phenomenon has been verified by several site investigations. It is very important to collect the microtremors data in large place with a high density to use to do our study on the ground character of the predominated period and exploration and imaging of the3D subsurface Vs structure. It will be adopted in the work of the seismic zoning and the construct quakeproof designing. Besides, it is expatiated that the development of the theory and the actuality of the research on the microtremors. This paper also describes the microtremors observation instrument, the selection of the observation time and the observation Place and the Principle of the observation line selection. Kinds of the analysis method are expounded and summarized and it makes a compared all round Presentation of the microtremors method. |
