A slow earthquake sequence on the San Andreas fault

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EARTHQUAKES typically release stored strain energy on timescales of the order of seconds, limited by the velocity of sound in rock. Over the past 20 years, observations and laboratory experiments have indicated that capture can also occur more slowly, with durations up to hours. Such events may be important in earthquake nucleation and in accounting for the excess of plate convergence over seismic slip in subduction zones. The detection of events with larger timescales requires near-field deformation measurements. In December 1992, two borehole strainmeters close to the San Andreas fault in California recorded a slow strain event of about a week in duration, and we show here that the strain changes were produced by a slow earthquake sequence (equivalent magnitude 4.8) with complexity similar to that of regular earthquakes. The largest earthquakes associated with these slow events were small (local magnitude 3.7) and contributed negligible strain release. The importance of slow earthquakes in the seismogenic process remains an open question, but these observations extend the observed timescale for slow events by two orders of magnitude.
Publication type Article
Publication Subtype Journal Article
Title A slow earthquake sequence on the San Andreas fault
Series title Nature
DOI 10.1038/383065a0
Volume 383
Issue 6595
Year Published 1996
Language English
Larger Work Type Article
Larger Work Subtype Journal Article
Larger Work Title Nature
First page 65
Last page 68
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