Changes of Transmission Waves due to a Single Fault

Effects of Fault Geometry on Transmission Waves

Abstract

In this paper, we focus on the effects of “an extensive single fault” on transmission waves. We first briefly review the studies with this concern. The effects of faults on seismic waves have received relatively little attention either theoretically or experimentally. Nevertheless, a number of theoretical and experimental works have been carried out mainly by N. G. W. Cook and his colleagues at the University of California, Berkeley. A theory for the reflection and transmission coefficients has been proposed and it has successfully explained experimental observations. As an example of this kind of study, we present our recent results of experimental work in which P- and S-waves with known wavelength were transmitted across a fault. The fault consists of evenly spaced square contacts, the size and the height of which were artificially controlled. We found that the transmissivity of the waves is solely determined by the ratio of the contact size to wavelength. The smaller the ratio is, the larger the amplitude of first arrival is for both P- and S-waves. We propose a mathematical model based on the stiffness of the fault. By comparing the transmission coefficients calculated by this model with the observed ones, we found that the model is not applicable if the ratio of contact size to wavelength is larger than 0.25. In this case, the amplitude of transmitted waves is found to be proportional to the real contact area.