Body-Wave and Earthquake Source Studies

Citation

Teng, Ta-Liang (1966) Body-Wave and Earthquake Source Studies. Dissertation (Ph.D.), California Institute of Technology. doi:10.7907/9VPH-AN84. https://resolver.caltech.edu/CaltechTHESIS:09282017-160405428

Abstract

The present work concerns a study on the radiation and propagation of seismic body waves. Based on a reformulated seismic ray theory and supplemented by the results of several associated boundary value problems, a method of body wave equalization is described which enables the extrapolation of body-wave fields from one point to another.

Applications of the above method to studies of earthquake source mechanism and earth's structure, specifically its anelasticity, are presented. The findings for two deep-focus earthquakes can be summarized by: (1) a displacement dislocation source, or an equivalent double couple, can generally explain the observed radiation fields, (2) the source time functions can be explained by a build-up step (1 - e ^-t/τ)H(t), and τ appears to be longer for larger earthquakes, (3) the total energy calculated from equalized spectrums is: for the Banda Sea earthquake (M = 6-1/4 - 6-3/4), E = 1.01x10²² ergs; and for the Brazil earthquake (M = 6-3/4 - 7), E = 2.56x10²³ ergs.

From the spectral ratios pP/P and P/P, it is found (1) that the upper 430 km of the mantle has an average Q_ɑ = 105, (2) that Q_ɑ increases very slowly until depth of about 1000 km, and (3) that Q_ɑ rises rapidly beyond a depth of 1000 km, remains a high value in the lower mantle and drops sharply toward the core-mantle boundary.

Thesis Files