Electronic Thesis and Dissertation Repository

Thesis Format

Integrated Article

Degree

Master of Science

Program

Geophysics

Supervisor

Molnar, Sheri E

Abstract

Seismic site effects arise from local geologic and topographic conditions, and modify incident earthquake ground motions at a site. Understanding variability in seismic site conditions is necessary for accurate assessment of seismic hazard. The microtremor horizontal to vertical spectral ratio (mHVSR) method is a cost-effective and non-invasive method to measure the site’s filtering effect in terms of an amplification frequency spectrum. Using a large, compiled database of mHVSR measurements from the Metropolitan Vancouver area, the impact of acquisition and processing parameter choices on the computed mHVSR is investigated. A robust processing algorithm is developed to batch process high-quantity mHVSR datasets. Products related to seismic microzonation hazard mapping, such as a regional map of the site fundamental frequency and the suite of unique mHVSR amplification spectra in the region are provided. This thesis exemplifies the practicality of using the mHVSR method for seismic site characterization.

Summary for Lay Audience

The ground shaking resulting from an earthquake can vary significantly between two proximal sites for the same earthquake. This variability is a result of variations in the local geologic and topographic conditions at a site, which act as a filter for the input ground motion and can modify characteristics of the incident motion such as amplitude, frequency, and duration. It is important to develop an understanding of how these site conditions vary throughout a region, and how incident earthquake motions are affected by these variable conditions so that the distribution of seismic hazard in an area can be accurately assessed. The microtremor horizontal to vertical spectral ratio (mHVSR) method has applications in providing estimates of parameters that are related to the ground motion modification experienced at a site. The method involves recording omnipresent microtremors using a three-component seismometer. Using a large database of single station microtremor measurements from the Metropolitan (Metro) Vancouver area, experimental setup and data processing decisions were studied to investigate their impact on the processed mHVSR result. A framework of suggestions is presented to aid future practitioners in carrying out effective surveys, as well as a novel processing algorithm, particularly well-suited for processing large datasets. The mHVSR database from Metro Vancouver was processed using this novel algorithm, and the processed results were used to extract parameters and create maps and other tools to aid in understanding the variability of site response in the region.

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