Electronic Thesis and Dissertation Repository

Thesis Format

Integrated Article

Degree

Doctor of Philosophy

Program

Civil and Environmental Engineering

Supervisor

Hong, Hanping

Abstract

The latest version of the Chinese seismic hazard map (CSHM) (i.e., fifth-generation CSHM) was developed based on the delineated seismic source model, which is defined based on geological and seismological information but also with some subjectivities. The results of the CSHM were presented in terms of peak ground acceleration (PGA) and peak ground velocity. No maps for spectral acceleration (SA) are given. This is partly due to the ground motion models (GMMs) to predict SA for mainland China are unavailable. The unavailability of the GMMs for SA results in the lack of uniform hazard spectra (UHS) that is important for structural seismic design.

There is a gap in the development of the new GMMs and seismicity models for Chinese seismic hazard mapping. This thesis is focused on the evaluation of the seismic hazard and the development of the uniform hazard spectra for mainland China. For the evaluation, a set of GMMs applicable to mainland China is developed by applying the so-called projection method. This method projects the GMMs developed for a reference region with a large number of historical records to a target region where the actual ground motions are scarce. For the projection, the NGA-West2 GMMs developed for California are considered for the reference region, and different regions in mainland China are considered as the target regions.

Rather than using the delineated seismic source model, smoothed seismic source regions based on the historical catalogue and spatial smoothing techniques are considered. Moreover, an analysis is carried out to assess the completeness of the historical Chinese earthquake catalogue. Two smoothed seismic hazard models for mainland China are obtained. The first one is based on cluster analysis and spatial smoothing by considering that a seismic magnitude-recurrence is applicable to a cluster, so the smoothing is carried out for the annual earthquake occurrence rate. The second one considers that the magnitude-recurrence relation is spatially varying, which is obtained by carrying out the smoothing by considering the earthquake magnitude (i.e., the smoothing the cumulative event count as a function of magnitude).

The CSHMs for mainland China are assessed using the newly projected GMMs, which could be used to predict the PGA and SA and the spatially smoothed seismicity models. A parametric investigation is carried out by considering different combinations of GMMs, magnitude-recurrence relations, and smoothed source models. The logic tree approach is used to represent the combinations. The newly developed CSHMs are presented in terms of PGA and SA. In addition, the uniform hazard spectra are developed for different locations within mainland China. A comparison of the newly developed seismic hazard maps to that of the fifth-generation CSHM indicates that they exhibit similar trends, although there are differences in the estimated return period values of PGA. A comparison of the normalized UHS to the standardized design spectrum in Chinese design codes is presented, indicating that the standardized design spectrum is conservative for short and long natural vibration periods.

Summary for Lay Audience

The seismic hazard maps are used as the basis to recommend seismic loads for structural design in codes and standards. The most recent Chinese seismic hazard map (CSHM) (i.e., the 5th generation CSHM) has been released. The map presents the estimated peak ground acceleration for a specified probability of exceedance per year. The estimated peak ground acceleration uses the delineated seismic source zones (the considered regions is delineated based on different seismic belts), magnitude frequency distribution relations, and ground motion models (GMMs) that estimates the ground motion for given earthquake events and distance. The presented study is focused on these three aspects of the modelling and assignments in order to assess seismic hazard for mainland China to study the adequacy of the reported seismic hazard by the 5th generation CSHM. New sets of the GMMs to predict the peak ground acceleration and spectral acceleration for different regions in mainland China are developed by using the projection method and based on the GMMs developed for the U.S. Spatially smoothed source models based on the historical earthquake catalogue, instead of using the delineated seismic source model, are proposed and examined. Besides, the use of spatially smoothed seismicity allowed the development of regional or site-dependent magnitude-recurrence relations.

By using the newly developed seismic source models, GMMs, and magnitude-recurrence relations, the seismic hazard mapping for mainland China is carried out using numerical simulation techniques. In addition, the site-dependent uniform hazard spectra (UHS), which are currently unavailable for mainland China, are developed. An extensive comparison of the resulting hazard map with the 5th generation CSHM is carried out. In general, the results for the peak ground acceleration are in agreement with that given by the 5th generation CSHM, although there are differences. The comparison of the UHS with the seismic design spectra recommended in Chinese structural design codes indicates that the latter can be conservative or unconservative depending on the fundamental natural vibration period of the structure.

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