A comparison of methods for the analysis of compressional,shear, and surface wave seismic data,and determination of the shear modulus |
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| Institution: | 1. National Sun Yat-sen University, 70 Lienhai Rd., Kaohsiung, Taiwan;2. National Chiao Tung University, 1001 Ta-Hsueh Road, Hsinchu, Taiwan;3. National Chiao Tung University, 1001 Ta-Hsueh Road, Hsinchu, Taiwan;4. Li-Jia Engineering Co., Ltd, Taipei, Taiwan;1. Hubei Subsurface Multi-scale Imaging Key Laboratory, China University of Geosciences, 388 Rumo Rd., Wuhan, Hubei 430074, China;2. Subsurface Imaging and Sensing Laboratory, China University of Geosciences, 388 Rumo Rd., Wuhan, Hubei 430074, China;3. Institute of Geophysics and Geomatics, China University of Geosciences, 388 Rumo Rd., Wuhan, Hubei 430074, China;1. Kansas State University-Geology Department, Manhattan, KS, USA;2. Kansas State University-Civil Engineering, Manhattan, KS, USA;1. Universidade da Madeira, CEris, Portugal;2. CEris, Instituto Superior Técnico, University of Lisbon, Portugal;3. TPF, Consultores de engenharia e arquitetura, SA, Portugal |
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| Abstract: | The seismic refraction method is commonly used to determine the lithology and stratigraphic geometry of geological sites. Beyond this application there is also the potential to extract additional velocity-related information such as mechanical properties of soils and rocks. However, this requires a reliable model of the subsurface velocity variations. Refraction data, P- and SH-wave first arrivals, and surface waves were analyzed using three different techniques: delay-time in combination with ray-tracing, tomography and multichannel analysis of surface waves (MASW). Results from the first two techniques were compared, which showed that sharp high-contrasting layering is best imaged by the traditional method, delay-time followed by ray-tracing. The tomographic method was unable to detect the water table in the P-wave survey but resolved near-surface gradational velocity changes. On the other hand, in the SH-wave survey the traditional method was not useful because of gradually increasing velocities, which were better suited to the tomographic method. Furthermore, to produce spatially detailed velocity-variation models the tomographic or the MASW methods are applicable. The MASW model showed somewhat lower velocities compared to the SH-refraction tomographic model and, in contrast, showed inverted velocity gradients. This study also presents a comparison between the shear moduli measured in situ, i.e. calculated from shear wave velocities, and determined using empirical relationships. The empirical relationship for sand gives higher values for shear moduli than those measured in situ. |
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