P- and SV-Wave Corner Frequencies over Low-Loss Paths: A Discriminant for Earthquake Source Theories.

摘要

Seismic data recorded at Jamestown, California, provide P- and SV-wave spectral corner frequencies for 18 trans-Sierra Nevada events in the range 3.2 < or = M sub L < or = 4.0. The ratio R of P- to SV-wave corner frequency was 0.96 + or - 0.17 for these events, which sample a wide range of source azimuths and focal mechanisms. Assumptions of a flat far-field source spectrum and frequency-independent attenuation in the 1-20 Hz band lead to Q sub beta not less than 480. This discrepancy indicates that R may be an extremely useful source-model discriminant, its variation indicating that different models need be applied to different source regions. R may lead to a clearer understanding of the physical processes associated with earthquakes; for example, the only source models that predict a value of unity for R at all azimuths are those in which the corner frequency measures the time duration of motion at the source, thus indicating that this duration is as long as the rupture propagation time across the source.