Abstract
Premonitory changes in seismic wave velocity and regional seismicity were successfully detected for the Izu-Hanto-oki, Japan, earthquake of 1974,M=6.9. Premonitory variation in gushing rate of hot springs, being consistent with the results of the seismological studies, suggests that the dry dilatancy model is favorable for the pre-seismic process of the present earthquake. The precursor time observed 9±1.5 years is in fairly good agreement with current magnitude-precursor time relations. The longer axis of the anomalous area is three times as large as the linear dimension of the fracture zone. Absence of significant pre-seismic upheaval of the crust seems to be attributed to the strike-slip nature of the focal mechanism.
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