On the Application of Surface Wave Surveys for Seismic Site Response Evaluation

Abstract: In sites where earthquakes occur, the use of surface wave methods represents a convenient and effective procedure for soil characterization. In particular, Multichannel Analysis of Surface Wave (MASW) has become a popular tool in many seismic micro-zoning projects. In common practice the active MASW method is implemented using a sledgehammer source and a linear receiver spread. This method is limited to shallow penetration depths (< 30 m). In sites where thick soil formations are present, an increased exploration depth is required. However, resolving >30 m depth profiles is a challenge if using active surface wave surveys. To increase the depth of S-wave velocity models towards and beyond 30 m depth, both a powerful low frequency source and a long receiver spread are needed. However, this generally demands a significant increase in the amount of equipment and fieldwork, which often makes the implementation of surface wave surveys impossible. The main objective of this thesis is to evaluate various aspects of the implementation of surface wave surveys to obtain reliable S-wave velocity profiles for seismic site response purposes. A proposed new methodology provides a possible alternative for increasing the depth of penetration, even in the case of only a standard 24-channel seismograph being available. This allows, without sacrifice to efficiency or accuracy, the optimal use of surface wave surveys to acquire velocity profiles and reduce survey costs. In the absence of a reference down-hole or cross-hole S-wave velocity profile, a single borehole sensor deployed at multiple depths was used to derive a reference S-wave velocity model. This alternative is especially beneficial in sites where earthquakes are frequent and the site response needs to be evaluated. This novel system provides a velocity model that can be used to test the reliability of inverted S-wave profiles obtained from surface wave surveys.