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Title: Site classification for seismic hazard assessment in low seismicity regions
Author: Tallett-Williams, Sarah
ISNI:       0000 0004 9350 2615
Awarding Body: Imperial College London
Current Institution: Imperial College London
Date of Award: 2018
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Probabilistic Seismic Hazard Assessment of low seismicity regions has significant uncertainty due to the limited catalogue of earthquake records. Part of this uncertainty relates to the modification of ground motions by near-surface geo-materials: site amplification. If the repeatable site amplification from strong ground motion stations (SGMS) is characterised, this uncertainty is reduced. Consequently, the uncertainty demands upon safety critical infrastructure can decrease, enhancing its resilience. However, the characterisation of site amplification effects is complex. Effective parameters can be prohibitively expensive to measure, particularly if full shear-wave velocity (Vs) profiles are required for multiple sites. This thesis aims to investigate an economical method to characterise near-surface site amplification. For 15 of the UK SGMS, geological models are developed and compared to the newly established Global Vs Database. The database is used to examine relationship of Vs with geological parameters. Relationships investigated include age and origin, but were only predominant in depth and grain size. A new Site Specific Proxy probabilistically correlates these characteristics with the geological profiles, making it possible to infer a probability distribution of a time averaged shear wave velocity (Vs30) for each site. Horizontal to Vertical Spectral (HVSR) ratio testing is performed to verify these station models. This in situ method, though indeterminate, is economical and proved accurate when examined against verification testing. The HVSR testing results of the UK SGMS correlate well with the Site Specific proxy estimates, having a mean difference within 18%, which is a significant decrease from other proxy methods. A method of Bayesian updating is developed for refining the Vs30 profiles and shows that one in situ test is generally sufficient to halve the standard deviation of the Site Specific proxy method. Thus, the economical combination of the Site Specific proxy and HVSR testing is recommended for site characterisation in low seismicity regions.
Supervisor: Stafford, Peter ; Fenton, Clark Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral