MEASUREMENTS OF THE STRAIN FIELD ASSOCIATED WITH EPISODIC CREEP EVENTS ON THE SAN-ANDREAS FAULT AT SAN-JUAN-BAUTISTA, CALIFORNIA

Over the past 6 years, repeated strain steps recorded on a tensor stra inmeter installed close to the San Andreas fault trace at San Juan Bau tista in California correlated closely with episodic creep events regi stered on a nearby creepmeter. The strain events were remarkably simil ar in character, were of about 1 hour duration, and were followed with in hours to days by creep events of 2-6 days duration. The episodic sl ip of a source region from 200 m to 500 m in depth and at most a few k ilometers in length is consistent with the observed strain and creep d ata. We postulate that the additional stress transferred to this regio n by the Loma Prieta earthquake is giving rise to an increased rate of accumulation of shear strain around a locked patch beneath the creep source region, thus accounting for the increased frequency of the cree p/strain events following the Loma Prieta earthquake.