Earthquakes: How big can they get?

A simple question, it seems. Discounting the tectonic effects of a giant impact, which could shake the whole planet, just how much of a shock could be generated entirely from within the Earth? The Richter scale is open ended, though the most powerful tremor on record was about 9.5; is an 11 or 12 possible?

I know that the force of a quake depends largely on the length of the fault involved, and the longest one known is about 1000 miles. But could entire plate boundaries move?

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Entire plate boundries do move ... albeit a few cm every decade or something like that ... but they still move, I think its involved with continental drift.

If a magnitude 10 earthquake were to happen, I would think it would come from a sudden, sharp shift in the continental plates. I wouldn't know if any of the other faultlines like the San Andres fault could generate a magnitude 10 tremor under it's own power.

 

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I think there was an earthquake back in 1811 or 1812 centered in the midwest (maybe Missouri) that was so strong that it changed the course of the Mississippi river. it could have been a Mag. 10 or greater I think...........

Yob Atta

 

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8.3, moment magnitude. Still pretty strong.

 

This was centered around the town of New Madrid, Missouri, in 1812. There are still earthquakes around that area.

The Mississippi flowed backwards for several weeks, as noted by some people. Just about the only evidence you can see today directly related to the 1812 quake is a fresh-looking oxbow lake next to the town.

 

Actually, a transform fault like the San Andreas does not produce such deep-seated earthquakes as ones found in subduction zones like Chile or Japan. Earthquakes in California rarely ever exceed 8.

Earthquakes that exceed 9 already can happen a few times around the globe in a century. In the 20th, there was one in Alaska and in Chile around the 1960s. So maybe, a mag. 10 can probably occur once every several to dozen millenia. But that's only mathematical extrapolation. No evidence has ever been found of a mag. 10 quake. So to speak, they're extremely unlikely. Especially when the earth is not as hot as it once was.

 

Make that more than 10000.

 

From what I read, 90% of all earthquakes originate from tectonic plates and the other 10% comes from faultlines. That would make sense considering that the "Ring of Fire" (Pacific Basin) is among the most seismically active area in the world.

The one you're talking about, Facial, is the strongest earthquake recorded in recent history, which is the Chilean earthquake of May 22, 1960, which is estimated at magnitude 9.5 ... which also happens to be the theoretical limit of earthquake strengths due to the finite dimensions of the tectonic plates.

 

I'm sure is the earth is ever pounded by a large asteroid over 6 miles in dia., you can be sure that it will generate some very large earth quakes (maybe 10 or more) and probably wake up a couple of sleeping supervolcanos too depending on where it hits........

Yob Atta

 

I don't think that there is any doubts that a fairly large asteroid could cause a magnitude 10 or greater earthquake upon impact. But if the movements of the tectonic plates/faultlines of the planet are only to be considered without any outside force ... such as asteroid impacts and human influence ... then I don't think a mag 10 quake is possible unless the tectonic plates themselves radically changes orientation.

 

Which fault is this?! Are you talking about the whole interconnected system of mid-oceanic ridges.

Thanks mate, we've been through that in at least 2 other recent threads. I was thinking of earthquakes generated without extraterrestrial influence.

 

Yeah. Those are faults, too.

 

That sounds about right. I don't think tectonic earthquakes can ever exceed mag.10.

 

Perhaps larger terrestrial planets could have more powerful tremors than Earth. - and correspondingly more destructive, given a higher surface gravity.

@Facial: if what you're saying about the mid-ocean ridges is true, then it's theoretically possible to have a GLOBAL quake. At least, under the oceans. Although, of course, it's hard to invent a viable geological source for the energy to drive it.

 

Interesting thought... This may have happened sometime in the distant past.

 

I suspect even the theoretical limit of mag. 10 was probably reached in earth's very distant past geological past. Who knows for sure what forces were active enough to have caused it. You can never-say-never because know one knows for sure.

Yob Atta

 

They were probably rare in the entire earth's history. But you can't rule out the possibility that it happened at least once within the past 4.6 billion years.

 

Plate Boundaries, particularly Subduction zones, are the sources of infrequent, super-Earthquakes.

The worst recorded (found in the Geological records) was an upper 9, and occured because the Subduction zone of the Juan De Fuca plate and the Pacific Plate got "stuck" and for some years the plates backed-up on themselves, until finally they gave way and WHAM. Nice fat Earth Quake that hit the entire Northern Pacific with a bigger Tsunami than that pup that hit Indonesia, India and that region just this Christmas.

 

Oh also, to answer the question, a 12 is about what it would take to shatter the Earth...so you can rule out 12s on the ricter scale.

 

Sorry to pop up with some n00bish questions... First of all, correct me if I'm wrong about this:
Earthquakes happen in the regions where multiple tectonic plates meet each other, right? And that should mean that quake epicenters can only be located anywhere around these areas, right? Does it mean that there's zero possibility that an epicenter can appear anywhere in the middle of a plate (like, maybe, somewhere in the middle of India, IIRC).

And please excercise my memory: what is a subduction zone?

Oh, and one more question: Can earth's rotation do anything about earthquakes? Like, would earthquakes be more common if earth rotated faster than it actually does today?