More Big Quakes in Chile

These are probably aftershocks, but I got these e-mails from the USGS about an hour ago:

Magnitude 7.2, Libertador O'Higgins, Chile 3/11/10 14:39:48 UTC
[This has since been revised down to magnitude 6.9.]

Magnitude 6.9, Libertador O'Higgins, Chile 3/11/10 14:55:30 UTC
[This has since been revised down to magnitude 6.7.]

Magnitude 6.0, Libertador O'Higgins, Chile 3/11/10 15:06:03 UTC

Aftershocks may continue for years after a quake in some cases, but these are strong. I couldn't say for sure whether these are indeed aftershocks or this is a new section of the fault breaking. Not my area of expertise, but I'll post a link if I can find anything on that after my class this morning.

What I'm finding strange about these earthquakes (aside from the third, which doesn't have first motion data and hence no focal mechanisms/moment tensors yet) is that they are not compressional, as you'd expect from the proximity to the subduction zone off of the Andes mountains. They are extensional. I'll have to look into this more after class as well.

As a note, revisions to magnitude are common as more seismograph stations worldwide pick up tremors from an event. The more data we have, the better we can characterize the motions and strength of the event.