Body-Wave and Earthquake Source Studies

• Main Author: Teng, Ta-Liang
• Format: Others
• Published: 1966
• Online Access: https://thesis.library.caltech.edu/10467/2/Teng_tl_1966.pdf; 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 <https://resolver.caltech.edu/CaltechTHESIS:09282017-160405428>

<p>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.</p> <p>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.</p> <p>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.</p>