[Skywise]

M8.0 - 99km NW of Iquique, Chile

Pacific Tsunami Warning Center

National Data Buoy Center

Brian

[Island Chris]

Brian has it pretty well covered. Is subduction great quake, and 2.1 m tsunami already reported in northern Chile.

Chris

[Island Chris]

The area of the quake had many foreshocks, including a M6.7 on March 16, 2014 (2 weeks ago). That M6.7 had foreshocks. The M6.7 had a gently NE-dipping plane, so likely on or associated with the subduction megathrust. The dip direction of the M8.2 is just a bit north of east, so pretty different, but when a fault is that flat, maybe the dip direction is not really such a difference in orientation (plus, the focal mechanisms may be a bit off, or the rupture of one or both of them could be complex).

A reminder that the Tohoku (Japan) M9.0 had a M7.4 foreshock a few days ahead.

Chris

[Island Chris]

There was a M7.6 aftershock; focal mechanism is thrust presumably on the same subduction megathrust as the mainshock. When you scroll down on the focal mechanism for the mainshock and for the aftershock, you get a rupture model including contours every 5 seconds of the rupture propagation, and amount of slip:

http://earthquake.usgs.gov/earthquakes/e...nite-fault

The main shock rupture looks to be about 250 km-long and 150 km-wide. The maximum slip was over 6 meters, but in a small area. I recall that the maximum slip for the M9 Tohoku quake was ten times more.

The text below is interesting, from:
http://www.washingtonpost.com/world/the_...story.html

(I saw it earlier elsewhere).

Chris


"And seismologists warn that the same region is long overdue for an even bigger quake.

“Could be tomorrow, could be in 50 years; we do not know when it’s going to occur. But the key point here is that this magnitude-8.2 is not the large earthquake that we were expecting for this area. We’re actually still expecting potentially an even larger earthquake,” said Mark Simons, a geophysicist at the California Institute of Technology.

"Nowhere along the fault is the pressure greater than in the “Iquique seismic gap” of northern Chile.

“This is the one remaining gap that hasn’t had an earthquake in the last 140 years,” said Simons. “We know these two plates come together at about 6, 7 centimeters a year, and if you multiply that by 140 years then the plates should have moved about 11 meters along the fault, and you can make an estimate of the size of earthquake we expect here.”

The USGS says the seismic gap last saw quakes of more than magnitude 8 in 1877 and 1868."