Method for rapid high-frequency seismogram calculation

We present a method for rapid, high-frequency seismogram calculation that makes useof an algorithm to automatically generate an exhaustive set of seismic phases with anappreciable amplitude on the seismogram. The method uses a hierarchical order of rayand seismic-phase generation, taking into account some existing constraints for raypaths and some physical constraints. To compute synthetic seismograms, the COMRADcode (from the Italian: ‘‘COdice Multifase per il RAy-tracing Dinamico’’) uses as core adynamic ray-tracing code. To validate the code, we have computed in a layered mediumsynthetic seismograms using both COMRAD and a code that computes the completewave field by the discrete wave number method. The seismograms are comparedaccording to a time–frequency misfit criteria based on the continuous wavelettransform of the signals. Although the number of phases is considerably reduced bythe selection criteria, the results show that the loss in amplitude on the wholeseismogram is negligible. Moreover, the time for the computing of the synthetics usingthe COMRAD code (truncating the ray series at the 10th generation) is 3–4-fold less thanthat needed for the AXITRA code (up to a frequency of 25 Hz).