Abstract
We present a method for rapid, high-frequency seismogram calculation
that makes use of an algorithm to automatically generate an exhaustive
set of seismic phases with an appreciable amplitude on the seismogram.
The method uses a hierarchical order of ray and seismic-phase generation,
taking into account some existing constraints for ray paths and some
physical constraints. To compute synthetic seismograms, the COMRAD
code (from the Italian: "COdice Multifase per il RAy-tracing Dinamico")
uses as core a dynamic ray-tracing code. To validate the code, we
have computed in a layered medium synthetic seismograms using both
COMRAD and a code that computes the complete wave field by the discrete
wave number method. The seismograms are compared according to a time-frequency
misfit criteria based on the continuous wavelet transform of the
signals. Although the number of phases is considerably reduced by
the selection criteria, the results show that the loss in amplitude
on the whole seismogram is negligible. Moreover, the time for the
computing of the synthetics using the COMRAD code (truncating the
ray series at the 10th generation) is 3-4-fold less than that needed
for the AXITRA code (up to a frequency of 25 Hz).
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