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7.6 magnitude earthquake south of Philippines
Earthquakes Hit Southern Philippines; No Damage : NPR
i am sure a bunch more stories will be popping up
Between 2004 and 2014, 18 earthquakes with magnitudes of 8.0 or more rattled subduction zones around the globe. That's an increase of 265 percent over the average rate of the previous century, which saw 71 great quakes, according to a report to the annual meeting of the Geological Society of America this week in Vancouver, British Columbia.
It’s clear that recent "great" earthquakes "triggered" related major quakes, says study author Thorne Lay, distinguished professor of earth and planetary sciences at the University of California, Santa Cruz. “If we look at all earthquake magnitudes, the past 10 years is not unusual in terms of the rate of events; the rate increases are just seen for events with magnitudes larger than 7.5 or so," he said. "This suggests that great events were ‘catching up’ on the plate boundary motions in several regions with fortuitous similar timing.” And by fortuitous, Lay means that he thinks it’s just coincidence that all those big earthquakes happened over the last 10 years.
Related quakes strike along same faults
So Lay isn’t suggesting that an earthquake in Japan or Sumatra is going to trigger a big one in the Cascadia subduction zone, the line along the coasts of Washington, Oregon and northernmost California where the oceanic plates dive under the continental plate. But, he says, a big earthquake at one end of a subduction zone might trigger others further down along the same fault. “This happened in Sumatra, where the great 2004 event activated the adjacent 2005 event, and those two activated a slightly more distant 2007 event,” he said. So what does that mean for the Cascadia subduction zone? “The offshore fault appears to be fully locked up by friction, with strain building up until the next large earthquake rupture releases it,” Lay says.
The Cascadia subduction zone, stretching from British Columbia to Northern California.
But nobody can predict exactly when that might happen, or what it will be like. “The last 10 years have been interesting for seismologists because we have learned that great subduction zone earthquakes occur in many different ways and there do not seem to be any simple rules to predict the kind of behavior to expect,” says Peter Shearer, a professor of geophysics at the Institute of Geophysics and Planetary Physics at the Scripps Institution of Oceanography at the University of California, San Diego. “Thus we can’t reliably assess at this point whether the Cascadia subduction zone will eventually break mostly in a single giant earthquake or a series of large earthquakes.” He said more study of past Cascadia quakes and those elsewhere, along with analysis of the recent crop of great quakes, might lead to better predictions.
Every 500 years ... or so
