Attenuation in the Western Great Basin
Final rept. 1 Oct 1984-30 Jun 1985
MACKAY SCHOOL OF MINES RENO NV SEISMOLOGICAL LAB
Pagination or Media Count:
In comparing teleseismic P-wave delays in the vicinity of the Central Nevada Test Site in Hot Creek Valley, NV, with P-delay data over a wider region in the Great Basin, we found that upper mantle speeds under Hot Creek Valley stations are higher than the average for the Great Basin as a whole, but lower than those beneath Pahute Mesa. These observations indicate that the caldera complex in Hot Creek Valley may have a high speed root similar to that proposed to exist beneath the Silent Canyon caldera at Pahute Mesa. In constrast, the Hot Creek Valley anomaly is not as strong as the Pahute mesa anomaly. The shadow zone caused by the Pahute Mesa structure is much more pronounced and consequently magnitudes of Pahute mesa explosions can be underestimated relative to the magnitude of Hot Creek Valley explosions of similar yield. Spectral amplitudes for 24 events of the Mammoth Lakes earthquakes sequence have been determined for the frequency range 0.1-10.0 Hz, including the M sub L 6 earthquake at 1450 UT on May 27, 1980. We have found nothing in the spectra of this event nor in the spectra of the aftershocks to distinquish them from spectra of tectonic earthquakes. However, the spectra themselves do not distinguish between various possible explanations for the non-double-couple source mechanism observed in moment tensor inversion and first motion data for the largest events of the Mammoth Lakes earthquake sequence. Journal reprints are included as appendices.