| AbstractRetrieving source
characteristics for moderate-sized earthquakes in sparsely instrumented
regions has been made possible in recent years, through the modeling of
waveforms at regional distances. The techniques used in such studies
model waveforms successfully at long period, using Green's functions for
simple 1D crustal models. For small earthquakes (M < 4), however,
long-period signals are usually noisy, and modeling short-period
waveforms requires refined Green's functions such as used in the
empirical Green's function (eGf) approach. In this article, we present a
new technique that generates such Green's functions by perturbing
individual generalized ray responses calculated from a 1D model. The
model is divided into blocks, and velocities in the blocks are allowed
to vary, which shifts the arrival time of the individual rays similar to
conventional tomography. The amplitudes of the rays are perturbed
independently to accommodate local velocity variations in the structure.
For moderate-sized earthquakes with known source mechanism and time
history, the velocity variation in each block and the amplification
factor for individual rays can be optimized using a simulated annealing
algorithm. The resulting modified Green's functions, pseudo Green's
functions (pGfs), can be used to study the relative location and
characteristics of neighboring events. The method is also useful in
retrieving 2D structure, which is essentially waveform tomography.Return to Table of
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