Earthquake Prediction: Absence of a Precursive Change in Seismic Velocities before a Tremor of Magnitude 3¾

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Science  20 Sep 1974:
Vol. 185, Issue 4156, pp. 1047-1049
DOI: 10.1126/science.185.4156.1047


P-wave velocities in the region near the source of a tremor of magnitude 3¾ 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.