Centroid single force inversion of seismic waves generated by land slides,
Kawakatsu, H.
J. Geophys. Res., 94,
12363-12374, 1989.
Abstract
The Centroid Moment Tensor (CMT) waveform inversion method
of Dziewonski et al. [1981]
is modified to analyze long period seismic waves generated
by ``single force'' events such as the gigantic landslides associated with the
1980 eruption of Mt. St. Helens.
We refer to the method as Centroid Single
Force (CSF) inversion.
As the result of the inversion we obtain the spatio-temporal centroid
and three components of a vector we call the CSF vector, which is the
seismic point source representation of a landslide and whose
direction is the opposite of the direction of sliding.
The scaler magnitude of the CSF vector
measures the overall size of the landslide and
is given by MCSF =MD, where M is the mass of the
sliding object and D is the sliding distance.
We apply CSF inversion to the long period surface waves generated by
the 1980 Mt. St. Helens event, the 1975 Kalapana earthquake,
and the 1974 Mantaro landslide,
using seismograms from the GDSN, IDA and HGLP networks.
The CSF solution for the St. Helens event is remarkably consistent
with the actual geological observations and
proves the efficacy of CSF inversion.
The CSF solution for the Kalapana event does not fit the overall waveforms
better than the CMT solution does.
However, because the CMT solution does not explain the observed Love wave
radiation pattern, it may be necessary to invoke a combination of
both types of mechanism for this event.
Although the geometry of the CSF solution (the direction of the force)
for the Mantaro event is consistent with the actual landslide,
MCSF is about 5 times smaller than that expected
from the mass and travel distance of the landslide estimated by geological
observations.
This discrepancy may suggest either the relatively aseismic nature
of this landslide
or that the total volume of the slide was overestimated.
By analogy to single station CMT inversion, single station CSF inversion
also appears to be stable and useful.