Earthquake frequency statistics, and probabilistic seismic hazard in southern California and New Zealand

摘要

Probabilistic Seismic Hazard Analysis (PSHA) is the subject of this dissertation. Chapters 1 to 4 address aspects of earthquake frequency statistics and fault mechanics, and investigate methods for evaluating PSH models. Chapter 5 incorporates the results of the earlier chapters to construct the first national PSH maps for New Zealand that consider both geological and seismological data.;In Chapters 1, I examine whether the magnitude-frequency distributions for individual faults are described by the Gutenberg-Richter relationship log(n/yr)=a-bM (n/yr is the number of events per year of magnitude M), or the characteristic earthquake model, in which the recurrence rates of the largest earthquakes are greater than the rates predicted with the Gutenberg-Richter relationship. I find that the distributions are generally described by the characteristic earthquake model. In Chapter 2, I examine whether the discrepancy between the seismicity rates predicted from the Working Group on California Earthquake Probabilities PSH model for southern California and the historical seismicity rate is statistically significant, and find that it is not. In Chapter 3, I identify the factors that are responsible for the largest differences between recent PSH maps produced for southern California by different workers. They are; the proportion of predicted earthquakes that are distributed away from the mapped faults, the maximum magnitude defined for a fault, and whether geodetic data are used to predict earthquake rates. In Chapter 4, I contribute to the development of precarious rocks as a field criteria to test the predicted ground motions of PSH models, by examining whether or not the site conditions at precarious rocks are equivalent to the "engineering rock" site conditions assumed in the PSH models. I find that the site conditions are equivalent to "engineering rock".;In Chapter 5, I undertake the first national PSHA of New Zealand that combines geologic and historical seismicity data. I identify a zone of high PSH that extends from the southwestern end of the country to the northeastern end, along the faults that accommodate most of the relative plate motion between the Australian and Pacific plates. Wellington city lies within this belt of high PSH.