| Summary: | 碩士 === 國立中正大學 === 地震研究所 === 101 === Soil liquefaction is a natural hazard that we can never ignore during a large earthquake. Soil liquefaction is normally occurred at somewhere near the surface, while the sandy soil is loose and having higher level of ground water. Soil liquefaction can potentially cause the surface constructions subsiding, inclining or collapsing, and damage the shallow buried light structures and lifelines. Soil spurts to the surface will affect crops in the farmland as well. This study utilized the P-wave refraction method and the multichannel analysis of surface waves (MASW) method to obtain the variation of the near surface P-wave and S-wave velocities in a particular site in southern Taiwan, where liquefaction occurred in 1946 and again in 2010. The purpose of this study is to investigate the correlation between the velocities variations of the seismic waves near surface and the liquefaction within and outside the liquefaction area. Totally, seven survey lines were deployed; results of the study show that velocities of the P-wave and S-wave are directly related to the area with soil liquefaction phenomena. For the areas not having liquefaction, velocities of the P-wave and S-wave are almost the same in the horizontal direction, but varied vertically from the ground surface down to the depth of 18 m. However, within the liquefaction area, the velocities of P-wave and S-wave in the horizontal directions are not varied significantly within 5 meters beneath the surface; major variances of the P-wave and S-wave velocities appear at between 5 and 18 meters below the ground surface. Within the soil liquefaction area, the velocity of S-wave is low; however, the P-wave velocity is higher in contrast. In addition, because of the saturated water content, variations of the P-wave velocity in the horizontal direction remain the same below the depth of 8 m. For the area not having liquefaction seen on the surface, velocity of the S-wave below the depth of 8 m is similar to that regions having liquefaction in the horizontal direction, which inferred that the region would have liquefaction under the surface within the entire area of all liquefied positions. Although evaluating the potential of occurring soil liquefaction in a large earthquake was commonly conducted by using an engineering method. In this paper, we show that the potential of soil liquefaction can be evaluated by using the velocities variations of seismic waves as well. In addition, the seismic method can be applied more efficiently to a broader region.
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