Premium
A comparison of broadband source spectra, seismic energies, and stress drops of the 1989 Loma Prieta and 1988 Armenian earthquakes
Author(s) -
Houston Heidi
Publication year - 1990
Publication title -
geophysical research letters
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 2.007
H-Index - 273
eISSN - 1944-8007
pISSN - 0094-8276
DOI - 10.1029/gl017i009p01413
Subject(s) - seismology , intraplate earthquake , geology , spectral line , seismic moment , subduction , hypocenter , fault (geology) , physics , induced seismicity , tectonics , astronomy
Broadband source spectra of the 1989 Loma Prieta (M W = 6.9) and 1988 Armenian (M W = 6.7) earthquakes are computed at periods from 1 to 50 sec using digitally‐recorded teleseismic P body waves. The effects of attenuation, geometrical spreading, and radiation pattern are removed from the spectra of individual stations, which are then averaged. The source spectra of the Loma Prieta and Armenian earthquakes are higher for their seismic moments than the spectra of 11 intraplate earthquakes studied by Zhuo and Kanamori [1987], which in turn are 2 to 4 times larger than average spectra of interplate subduction zone earthquakes. The seismically radiated energy can be computed from the source spectrum using Haskell's [1964] formulation assuming a point source with no directivity. An Orowan stress drop can be obtained from the seismic energy and moment. The Orowan stress drops for the Loma Prieta and Armenian earthquakes are both about 20 bars, significantly higher than Orowan stress drops of recent large interplate earthquakes. There is a positive correlation between the Orowan stress drops and the estimated repeat times, consistent with the notion that mechanical fault strength increases with increasing interseismic period.