Baisch, S., Bokelmann, G. H., 2001,
Seismic waveform attributes before and after the Loma Prieta
earthquake: Scattering change near the earthquake and temporal
recovery, Journal of Geophysical Research 106, 16323-16338
During 1987 to 1995 several clusters of nearly identical seismic events
(multiplets) occurred near the Loma Prieta source region. These multiplets allow
us to
investigate and demonstrate spatial and temporal changes in seismic wave character
associated with the 1989 Loma Prieta main shock.
For seismogram pairs, we use a moving window technique to compute
coherencies depending on lapse time and frequency.
Post-Loma-Prieta events have reduced coherencies with pre-Loma-Prieta
events
in a spatially limited region close to the Loma Prieta hypocenter,
while other paths remain nearly unaffected.
These changes gradually recover within a time interval of five years
after the Loma Prieta earthquake.
A possible explanation for the time dependence
are coseismically opened cracks which cause scattering increase for wavefields after
the Loma Prieta event.
Postseismic relaxation processes such as crack healing, fluid diffusion or
after-deformations lead to progressive closure of these cracks
with time after the main shock. Thus the scattering properties of the
local crust
approach the pre-main-shock state.
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