An investigation into earthquake ground motion characteristics in Japan with emphasis on the 2011 M9.0 Tohoku earthquake

Author

Hadi Ghofrani, The University of Western OntarioFollow

Degree

Doctor of Philosophy

Program

Geophysics

Supervisor

Gail Marie Atkinson

Abstract

In this integrated study, ground-motion characteristics of one of the most devastating earthquakes in history, the 11^th March 2011 Tohoku-oki earthquake (moment magnitude (M) 9.0), are investigated. The investigation centers on developing empirical and simulated-based ground-motion prediction models for this earthquake. These models allow prediction of expected ground motions from large interface (mega-thrust) earthquakes and estimation of their variability due to variability in input parameters, specifically source characteristics (e.g. slip distributions), propagation path, and site effects.

This research work can be divided into two main parts. In the first part, the influence of regional geologic structure, in particular the attenuation effects of seismic wave amplitudes with distance while traveling through a volcanic arc region (fore-arc versus back-arc attenuation), is empirically evaluated using regression analysis of Fourier amplitude spectra (FAS) of well-recorded Japanese events. It is concluded that the separation of fore-arc and back-arc travel paths results in a significant reduction in the standard deviation (“sigma”) of ground motion predictions (by as much as 0.05 log10 units). The distinction between fore-arc and back-arc attenuation has important implications for hazard analysis in subduction regions.

In the second part, the ground-motion characteristics of the 2011 Tohoku earthquake are investigated. First, site response in Japan is thoroughly characterized using thousands of surface and borehole recordings. Site amplification effects are found to be very strong at most sites, often exceeding a factor of five. It is concluded that the large observed ground-motion amplitudes at high frequencies during the Tohoku event are mainly due to the prevalence of shallow-soil conditions in Japan that amplified higher frequencies.

A stochastic finite-fault model was used to simulate average response spectra of the Tohoku earthquake, for comparison with observed ground motions. The simulation results show that use of a source model comprised of several rupture asperities produces ground motions that are in good agreement with the observations at both high- and low-frequency ranges, and also provides an accurate description of the temporal characteristics of observed ground motions. The calibrated model for the 2011 Tohoku earthquake can be utilized to predict ground motions for future large events in other regions, such as the Cascadia region of North America, by suitable modifications of the regional attenuation and site parameters.

Recommended Citation

Ghofrani, Hadi, "An investigation into earthquake ground motion characteristics in Japan with emphasis on the 2011 M9.0 Tohoku earthquake" (2012). Electronic Thesis and Dissertation Repository. 887.
https://ir.lib.uwo.ca/etd/887