Peru-Chile Could Experience Megathrust Quake as Six Quakes Over 6 Mag Strike Area

Menedes567
True American, do you think something unprecedented is going on with plate movement activity of the Nazca plate rubbing against the South American Plate at a rate much more faster and violent than before? I don't have much expertise on this area of study in terms of geology, so I would like to ask for your insight and opinion.

Well first, the Nazca plate is subducting underneath the South American Plate. And "unprecedented" to scientific minds isn't necessarily unprecedented to me. In fact, I have suggested here before in a thread long ago that this could be possible. I mean if, just IF, something like a major movement of the plate were to occur all at once- and it was to slide some 500 meters further under SA all at once- what would be the likely precursors?

Well, look at that pic above I just posted. We'd likely see seismicity at varying points, shallow, mid, and deep, all along the fault length and at depths corresponding to the slab depth profiles. And well- just look at that pic. Like that. Or worse. In other words, we'd probably see the pressure releases from these quakes all over the plate interface at depth as it began to move.

Now really, it would be pretty far fetched to suggest such a thing. But I am a pretty far fetched kinda guy. No, I don't think it will happen. But I contend it could. And I contend this is the kind of activity we'd see if it were going to.

Update: fault still moving, and quakes just keep happening over and over, like there's no stopping it.

reply to post by muzzy

Especially the opening lines, where you said:

Ha! you were right about it leading to a big one!,

but I'd hold back on calling it a MEGATHRUST quake.

I know you were responding to TA, but I'd also like to know why you don't really agree with calling it a megathrust event. Do you have data about the mechanisms involved that tell you it was something other than the kind of thrust faulting that is generally defined as "megathrust"? If so, I think we'd be interested to know what, in your opinion, it actually was.

reply to post by TrueAmerican


You are not the only one worried about a larger quake, TA. There are a few seismologists warning of just that--you're in good company.

More aftershocks and even a larger quake could not be ruled out, said seismologist Mario Pardo at the University of Chile.

From NBC news
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This from a Cornell professor:

The fault that triggered a magnitude 8.2 quake off the northern Chilean coast was overdue for a significant earthquake, and an even more powerful temblor could be in store, said Rick Allmendinger, a Cornell University professor of earth and atmospheric sciences.

Allmendinger goes on to say:

“It’s probably not big enough to have released all of the energy that had been stored up along that locked plate boundary for the last 140 years or so,” Allmendinger said. “Is this the Big One for that area? Or was it a foreshock to a presumably an even bigger earthquake?”

www.latimes.com...

www.latimes.com...
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And from CalTech:

"This magnitude 8.2 is not the large earthquake that we were expecting in this area," said Mark Simons, a geophysicist at Caltech in Pasadena, California. "We're expecting a potentially even larger earthquake."

From CNN

Hmm, well that 5.8 in Panama is now curious. I suppose if the Nazca Plate is mad at the world and is going to move, we should start seeing more quakes along its western, northern, and southern edges too. This means the East Pacific Rise and the Chile Rise. So I guess we'd better keep an eye out for those. Pull a thirty day at USGS, and you will see that some have indeed occurred there.

I really don't think that's going to happen. Of course no one thought Japan would happen either. Not there where it did.

Southern Chile Coast and Northern Peru Coast will no doubt react to the stress redistributions from this 8.2. It might be a while.

reply to post by JustMike

OK, lets call it a MEGATHRUST quake then.
its the MEGA bit that threw me, now I look it up its what they call these offshore thrust faults, magnitude has nothing to do with it.
Sorry for the mix up.
To me MEGA means HUGE, 8.2 is BIG, but not HUGE.
HUGE to me is 8.7+, especially if it is on land

There was just a 6.4. That can't be a good sign that an aftershock went up in intensity from the previous ones:

earthquake.usgs.gov...

hearing about a 7.4 about 15 mins ago...is this accurate?

that is a lot of activity!

reply to post by Salamandy


It's just been upgraded to a 7.8:

earthquake.usgs.gov...



This is not good....

reply to post by _BoneZ_


i dont know crap about earthquakes but this is like counting contractions for a pregnant woman.

sooner or later the big deal is coming.

has the Nazca plate called it's doctor yet to see if it should go to the ER? only time will tell...

Just got home right now, opened up my rig and seeing the S-waves all over the place. I warned against a high 7, and there it is. This is NOT good. That just broke the rules again. At this point, the people of Chile had better watch the hell out and prepare. An 8.8+ is possible soon.

Aww man. This sucks. I am so sorry peoples of Chile and Peru.

EDIT: Even at 7.6 after the downgrade, that STILL breaks the rules. Likely it is a foreshock now. Never can tell for sure. But damn. Just damn.


EDIT2: And what's really going to suck is if it hits at night. Because the tsunami it's going to cause will be coming in the dark. *Shakes head.*

If these are foreshocks in Chile, what the hell would the big humdinger look like ?!

Japan's foreshocks were in the upper 6's before the 9.0 hit...

the biggest aftershock of the M8.8 in 2010 was M6.9 according to University of Chile (GUC) scroll upwards from the Blue icon 2010 on the left menu on this interactive map Chile 2000-2012 M6+
so this 7.6Mw is way out of proportion to the standard aftershock for a 8.2Mw
doesn't look good.

reply to post by muzzy


damn, if we've even got muzzy saying this don't look good... Then maybe that's cause...

This don't look good!

I guess he finally emerged from his eternal skepticism.

Another 6.2 aftershock...or foreshock... or wtf. I just don't know anymore. It's all running together now. The fault is agitated beyond belief as I watch this in spectro. Jesus.

Northern Ecuador and Columbia...lookout. That lone quake off Panama. Something about that in the midst of all this... Dunno. It seems the whole plate interface is reacting to this. What's in store next is anyone's guess. But my eyes are glued. And I gotta get to sleep sometime tonight. wtf.

TA, the one thing that keeps me interested in monitoring the data on earthquakes is the surprises, there always seems to be something out of the norm just around the corner
I seem to have missed the 30th's data on this graph, so disregard the gap there please. I'll do it again from scratch in the morning to make sure there haven't been any revisions.

(click image for larger version, opens in new tab/window)

reply to post by muzzy


Thanks for the graph. You noticed where EMSC is placing the epicenter of that 7.6, compared to where USGS is placing it? I mean that's a pretty radical difference. Like a 40 km or more difference. EMSC has it out at sea.

Guys, do you we could see a repeat of the 9.5 quake back in 1960?

reply to post by TrueAmerican

GUC are offshore too, to the SE of the main cluster of previous events.
www.sismologia.cl...
-20.517, -70.439

reply to post by muzzy

Thanks for your reply, Muzzy.

I take your point on what we generally think if we hear of a "megathrust" quake. Most of us think of something huge -- perhaps even bigger than that 8.2 Mw. To be honest, I suspect even the top professionals think along the same lines when they're looking at real events. I was asking mainly because many readers place a lot of stock in the opinions of the "quake geek" members like PuterMan, TrueAmerican, yourself and a few others -- and for good reason. So I was just making sure that you're all on pretty much the same page from the standpoint of the technical definition. Nothing more than that.

reply to post by JustMike


Well I agree it is one of the smaller megathrust quakes. But an 8.2 Mw out at sea directly on the Peru-Chile Trench thrust fault is by definition, a megathrust quake. But fine, if a 9+ happens, I'll agree to call it a SUPER megathrust quake. How's that?

reply to post by TrueAmerican

Yes. So would I. I also think the pros in the business would be thinking along the same lines as you guys. I was just asking for clarification because you and Muzzy know a lot more about this stuff than I do.