Earthquake prediction: Absence of a precursive change in seismic velocities before a tremor of magnitude 3 3/4

Abstract

P-wave velocities in the region near the source of a tremor of magnitude 3 3/4 were constant to within 2 percent for 41 days before the event; no evidence of a precursive change in velocity was found. Observations of S-wave velocities and the ratio of P-wave to S-wave velocities also showed no precursive changes. In recent studies, premonitory changes in body-wave velocities of about 10 percent and having a duration of 2 to 3 weeks have been reported for crustal earthquakes of this size.