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Tensor
2012-Apr-11, 06:36 PM
Via USGS there was a magnitude 8.6 earthquake (http://earthquake.usgs.gov/earthquakes/eqinthenews/2012/usc000905e/) off the coast of Norther Sumatra at UTC 8:38 today. Estimated depth was 14 Miles. A magnitude 8.2 earthquake (http://earthquake.usgs.gov/earthquakes/eqinthenews/2012/usc00090da/) struck at 10:43 UTC within three and a half degrees lateral and above the first. Depth for the second one was estimated at 10 miles. Location of the first quake was at 2.31 North, 96.03 East. Location of the second was at .77 North, 92.45 East. Tsunami watches were originally issued, but latter cancelled.

geonuc
2012-Apr-11, 07:16 PM
The moment tensor solutions (beachballs) for both earthquakes indicate strike-slip movement, which does not generate tsunamis.

dgavin
2012-Apr-11, 07:48 PM
There was aloso a 6.0 much further west in the india ocean as well. This looked to occur at a spot where there is a very isolated undersea mountain.

Tensor
2012-Apr-11, 09:01 PM
The moment tensor solutions (beachballs) for both earthquakes indicate strike-slip movement, which does not generate tsunamis.

I was going to edit to add the strike-slip part, but I got called away before I could. Thanks.

Trebuchet
2012-Apr-11, 11:23 PM
Still must have been very scary for people who lived through the 2004 event.

Ara Pacis
2012-Apr-12, 08:16 AM
It's been a busy day for earthquakes. There was also a 5.9 near Oregon, a 6.5 on the west coast of Mexico and as of an hour ago, a 6.9 in Baja California. Or maybe that's not busy as such things go.

geonuc
2012-Apr-12, 08:59 AM
I was going to edit to add the strike-slip part, but I got called away before I could. Thanks.

No problem. I was online shortly after the first quake happened and checked the USGS site. They already had the beachball posted, so I knew there was no tsunami threat. So, that got me to thinking about the inevitable warning that would be issued. Sure, a big temblor off the coast of Sumatra will scare a lot of people, but the science and infrastructure behind determining movement along the fault is fairly robust, and as we saw here, provides fairly quick answers.

Tensor
2012-Apr-12, 02:53 PM
It's been a busy day for earthquakes. There was also a 5.9 near Oregon, a 6.5 on the west coast of Mexico and as of an hour ago, a 6.9 in Baja California. Or maybe that's not busy as such things go.

Some big astronomical alignment, I'm thinking. OH, I can't do this with a straight face. :rofl:

Rhaedas
2012-Apr-12, 03:06 PM
Some big astronomical alignment, I'm thinking. OH, I can't do this with a straight face. :rofl:

It's true. Something is always aligned with something.

Wouldn't the ones on the US/Mexico West Coast be indirectly tied together? Maybe one causing the other that was under stress to slip?

Tensor
2012-Apr-13, 02:42 AM
It's true. Something is always aligned with something.

Wouldn't the ones on the US/Mexico West Coast be indirectly tied together? Maybe one causing the other that was under stress to slip?

Yeah, it's very possible. You relieve stress on one section, it can increases stress on another, which then releases the stress with another earthquake. Doesn't mean it always happens, but the chance is there. After looking at dgavin's list on quakes this week (in the other thread), it appears that many of the strong quakes are either related or aftershocks of the first quake in each area.

dgavin
2012-Apr-13, 07:56 PM
Yeah, it's very possible. You relieve stress on one section, it can increases stress on another, which then releases the stress with another earthquake. Doesn't mean it always happens, but the chance is there. After looking at dgavin's list on quakes this week (in the other thread), it appears that many of the strong quakes are either related or aftershocks of the first quake in each area.

I would go so far as saying, that it's startign to look remotly possible that they are related(aftershocks) to the sieries of now three Mega-Thrust earth quakes. Each one of those reduced the diameter of the planet by a number of meters, which puts additional stress on the entire pacific plate over all.

This incresed stress also may increase the chances slightly of a Mega-Thrust event along the subduction area's that have not yet had one in recent millenia.

The following is the predicted range of magnitudes of mega-thrust events based on remaining locations.

Juan-de-Fuca Subduction zone: Mag 8.0 - 9.7
Aleutian Trench Subduction zone: Mag 8.5 - 10.5*

* The Aleutian Trench does not appear to have regular mega-thrust events as the other subduction regions do, because of the steep angle the pacific plate dives under there (a 45 degree angle). An event here would be extreamly unlikely. However it is possible that the last large event there caused the pacific plates change of direction some 80mill years ago, evidenced by the the sudden turn seen in the path of the chain of mountains from the hawaii hot spot. If the entire span of the Aleutian subduction region releases at once (some 3200km) it would be a mag 10+ event, enough energy to jostle the pacific plate itself around, possibly altering it's direction of travel again.

geonuc
2012-Apr-13, 08:37 PM
The shift in Pacific plate motion, as evidenced by the 'bend' in the Hawaii-Emperor seamount chain, may have been caused by plate reorganizations elsewhere in the Pacific. Such as a spreading ridge being overrun or the start of a subduction. I've not read anything suggesting it might have been because of movement at the Aleutian trench. But maybe.

Ara Pacis
2012-Apr-17, 11:38 AM
A 6.7 quake near Valparaiso, Chile and a 6.8 near Papua-New Guinea.