Charactristic Of Long Period Microtremor And Its Application In Seismic Hazard Prevention

Shear wave velocity (Vs) of soil is one of the key parameters used in seismic engineering and geotechnical engineering; which is an important parameter in evaluation of dynamic properties of a site. It is well known that the micro tremor observation is one of the most convenient methods to investigate the dynamic characteristics of the surface ground for no need of man-made explosion source which caused by human activities such as traffic vibrations and environmental noise from storm and ocean waves. The micro tremor is a kind of geophysics prospecting and drilling information, which is of abundant intention such as the information of soil site and engineering geological condition and so on.As the long period microtremor signal is very faint, which range can reach only a few microns, it is needed a widely frequency band, high sensitive and low noise detector to obtain the collect high fidelity effective wave data. Since the major source of the microtremor signal to reach exploration depth up to tens of meters is the ocean wave, storm and such natural phenomena, For the, it is easy to obtain strong signal in Japan and the coastal area in China. However, it is needed to discuss whether an effective long period microtremor signal can be obtained in mainland which far away from the ocean in Chinese, where the geological and environmental condition changes a great deal. Also, the research about microtreomor signal's properties including the strongest and the weakest signals and the spectrum feature needs to be discussed urgently.Based on the detailed describe of the present status and the problems on the microtremor survey, long period microtremor survey and microtremor array survey, using microtremor observation principle and choosing the area from coastal region to the part far away from coastline with several comparison points setting on the coastal region and the intermediate area, a series of regular long-term continuous long period microtremor survey and a great number of single points microtremor survey are conducted. Chinese inland area's microtremor signal are observed and studied. The measurement method of long period microtremor survey, equipment and parameter selection, data quality guarantee measures and long period microtremor properties and its application in the site predominant characteristic evaluation are discussed. The variation of characteristics of microtremor from coast to inland areas is clarified, especially the variation of the long period microtremor. The spectrum stability of the microtremor is evaluated. Detailed information about thickness of sediment layers and the lateral variation are revealed, with the comparison to the microtremor survey's applicability in the coastal area and inland areas.In the aspect of the long period microtremor survey's application in earthquake and disaster prevention, there are many works have been done. First, based on the east-west microtremor survey data in Shanghai, single point spectrum analogy method is used for the east-west cover soil distribution inversion in Shanghai. It is compared to previous large scale underground survey data, and the underground survey application of the long period microtremor survey is valued. Then, understanding the long period microtremor feature in Chinese wan area, we carry out array microtremor survey in allusion to the coastal city Shanghai. In addition to this, array microtremor survey method and its analytical method is detailed discussed, also the applicability that using the array microtremor survey method to calculate underground shear wave velocity distribution.