The collective synchronization of great earthquakes

Charles G. Sammis, & Stewart W. Smith

Submitted 2012, SCEC Contribution #1668

Nature letters do not have abstracts - Here is the lead paragraph:

A plot of great earthquakes (magnitude Mw>8.0) since 1900 shows periods of enhanced activity: roughly between 1900-1910, 1950-1965, and from 2005 to the present1,2 (Fig.1). The significance of these temporal clusters has been questioned for two reasons: 1) the periods of increased activity could be Poisson clusters in a random distribution, and 2) no plausible physical mechanism has been proposed to explain worldwide temporal clustering3,4. Here we show that by representing great earthquakes as a system of coupled non-linear relaxation oscillators, we can explain the observed temporal clustering as a consequence of the collective synchronization of their seismic cycles. The coupling mechanism comes from recent observations that the seismic waves from a great earthquake can trigger an episode of slow slip on the deep extension of a distant fault5,6. If two large faults interact such that an earthquake on one produces deep creep on the other (and vice-versa) and if this creep loads the more brittle shallow layers of the fault thereby advancing it seismic cycle, we will show that their seismic cycles can become synchronized. Although it has been observed that great earthquakes can trigger seismicity at great distances7,8, we emphasize that the mechanism proposed here does not involve the direct triggering of distant earthquakes, but rather a more subtle coupling through deep creep that modifies the seismic cycles to produce an emergent alignment of their cycles and, thereby, the observed temporal clustering.

Citation
Sammis, C. G., & Smith, S. W. (2012). The collective synchronization of great earthquakes. Nature, (submitted).