We bring you the latest in our ongoing coverage of earthquakes. To recap what’s happened recently: An magnitude 8.8 earthquake – one of the largest earthquakes ever recorded – struck Chile on February 27. A magnitude 7.0 earthquake devastated Haiti on January 12, killing upwards of 200,000 people. And in the meantime (as we reported earlier), scientists’ fears that the Haiti quake forewarns increased seismic activity seem to have been realized. In light of the Chile quake, too, reports of the hundreds of small tremors that have been rocking Yellowstone National Park over the past few weeks are more troubling. As if all this wasn’t enough, the United States Geological Survey is reporting that it recorded a magnitude 3.8 earthquake in northern Illinois (see also the NY Times article) – an area normally free of seismic activity.
One question on everyone’s mind, then, is this: are the Chile and Haiti earthquakes in any way related? The answer is this:
They may have the same parent. Most seismologists agree that the
Haitian quake didn’t cause Saturday’s event in Chile. Earthquakes occur
when the stress on a tectonic plate overcomes the friction holding it
in place. The last stress-relieving earthquake at this location in
Chile occurred in 1835. Since then, friction has held the edge of the Nazca plate in place while the rest of it slid 10 to 12 meters underneath the neighboring South American plate.
As a practical matter, that displacement was the sole cause of
Saturday’s earthquake. But displacement isn’t the only thing stressing
a tectonic plate. Tides, dammed-up rivers,
and pressure from other shifting plates can play a supporting role.
Major earthquakes may shift plates slightly and thus increase the
stress along fault lines. If another earthquake was poised to happen at
some point soon, the added stress from a first quake could serve as a
catalyst. While the Haitian earthquake really wasn’t big enough to have
that effect in Chile, some seismologists believe the much stronger
Sumatran quake of 2004–and maybe even the 1960 Chilean quake, the most
powerful ever recorded–may have set the stage for both of them.
Unsettling (forgive the pun – it’s probably not appropriate, to be honest). You can read more here.
Edit: Update: I neglected to mention that the Chile quake altered the earth’s axis and shortened the length of the day.
Pretty insightful post. Never thought that it was this simple after all. I had spent a good deal of my time looking for someone to explain this subject clearly and you’re the only one that ever did that. Kudos to you! Keep it up