Whether last weekend's 6.5 magnitude temblor off the coast of Northern California's Humboldt County and the Haiti earthquake two days later are linked is yet to be determined. Seismologists now widely recognize that a large earthquake in one place can trigger another vulnerable fault thousands of miles away. Yeats calls it the "pulling the buttons off your shirt" idea—by releasing tension on one stressed point, the force shifts and can rupture another "locked" point. "You pull one button off," he said, "and the next one is ready to go." A paper published last October in Nature reported the large 2004 seismic events near the Indonesian island Sumatra that spurred the devastating Indian Ocean tsunami had an impact on the San Andreas fault in California.
In the meantime, seismologists will be watching Haiti closely, Blanpied noted in the USGS podcast, and they expect to see aftershocks for days to come. The largest aftershocks so far have already rumbled in at magnitude 5.9, and more could strike at any time.
And Yeats is not convinced that this latest quake at Haiti is the most severe one the Caribbean is likely to see in the near future. "It's not the big one," he said in a January 13 follow-up interview. He added he is now worried that a larger one could hit other cities in the region, such as Santa Domingo in the Dominican Republic or Kingston, Jamaica. The Caribbean Plate, he noted, is "just sort of sitting there while the North American and South American plates move" west (due to sea floor spreading in the Atlantic). But the next big earthquake could be years or decades from now, he said. "We're good at placing these forecasts and probabilistic terms on a geological time scale, but we're not good at putting it at scales that matter to you and me." And even probability forecasts can turn out to be wrong. The southern San Andreas was pegged as likely to produce a major earthquake before this one was, he noted.
Read more about these hazards in ScientificAmerican.com's In-Depth Report on earthquakes.