Seismologists puzzle over largest deep earthquake ever recorded

Seismologists puzzle over largest deep earthquake ever recorded
This is a map showing the location of the Sea of Okhotsk. The sea is bordered by Russia and Japan. Credit: Wikipedia.

A magnitude 8.3 earthquake that struck deep beneath the Sea of Okhotsk on May 24, 2013, has left seismologists struggling to explain how it happened. At a depth of about 609 kilometers (378 miles), the intense pressure on the fault should inhibit the kind of rupture that took place.

"It's a mystery how these earthquakes happen. How can rock slide against rock so fast while squeezed by the pressure from 610 kilometers of overlying rock?" said Thorne Lay, professor of Earth and planetary sciences at the University of California, Santa Cruz.

Lay is coauthor of a paper, published in the September 20 issue of Science, analyzing the seismic waves from the Sea of Okhotsk . First author Lingling Ye, a graduate student working with Lay at UC Santa Cruz, led the seismic analysis, which revealed that this was the largest deep earthquake ever recorded, with a seismic moment 30 percent larger than that of the next largest, a 1994 earthquake 637 kilometers beneath Bolivia.

Deep earthquakes occur in the between the and , from 400 to 700 kilometers below the surface. They result from stress in a deep subducted slab where one plate of the Earth's crust dives beneath another plate. Such deep earthquakes usually don't cause enough shaking on the surface to be hazardous, but scientifically they are of great interest.

The energy released by the Sea of Okhotsk earthquake produced vibrations recorded by several thousand around the world. Ye, Lay, and their coauthors determined that it released three times as much energy as the 1994 Bolivia earthquake, comparable to a 35 megaton TNT explosion. The rupture area and rupture velocity were also much larger. The rupture extended about 180 kilometers, by far the longest rupture for any deep earthquake recorded, Lay said. It involved shear faulting with a fast rupture velocity of about 4 kilometers per second (about 9,000 miles per hour), more like a conventional earthquake near the surface than other deep earthquakes. The fault slipped as much as 10 meters, with average slip of about 2 meters.

"It looks very similar to a shallow event, whereas the Bolivia earthquake ruptured very slowly and appears to have involved a different type of faulting, with deformation rather than rapid breaking and slippage of the rock," Lay said.

The researchers attributed the dramatic differences between these two deep earthquakes to differences in the age and temperature of the subducted slab. The subducted Pacific plate beneath the Sea of Okhotsk (located between the Kamchatka Peninsula and the Russian mainland) is a lot colder than the subducted slab where the 1994 Bolivia earthquake occurred.

"In the Bolivia event, the warmer slab resulted in a more ductile process with more deformation of the rock," Lay said.

The Sea of Okhotsk earthquake may have involved re-rupture of a fault in the plate produced when the oceanic plate bent down into the Kuril-Kamchatka subduction zone as it began to sink. But the precise mechanism for initiating shear fracture under huge confining pressure remains unclear. The presence of fluid can lubricate the fault, but all of the fluids should have been squeezed out of the slab before it reached that depth.

"If the fault slips just a little, the friction could melt the rock and that could provide the fluid, so you would get a runaway thermal effect. But you still have to get it to start sliding," Lay said. "Some transformation of mineral forms might give the initial kick, but we can't directly detect that. We can only say that it looks a lot like a shallow event."

Explore further

Strong earthquake at exceptional depth

More information: "Energy Release of the 2013 Mw 8.3 Sea of Okhotsk Earthquake and Deep Slab Stress Heterogeneity," by L. Ye; T. Lay et al. Science, 2013.
Journal information: Science

Citation: Seismologists puzzle over largest deep earthquake ever recorded (2013, September 19) retrieved 15 September 2019 from
This document is subject to copyright. Apart from any fair dealing for the purpose of private study or research, no part may be reproduced without the written permission. The content is provided for information purposes only.

Feedback to editors

User comments

Sep 19, 2013
I've been connecting this little phenomenon for a long time on a laymen level, but has anyone else ever noticed that earthquakes co-relate to solar flare activity???

-large solar eruption
-time and distance traveled
-magnetic funnel concentrating an energy infusion at the poles beamed to the core
-energy infusion results in increased convection of magma material both magnetically and thermally
-eventually, an extraordinary earthquake.

.... from a laymen's intuitive perspective

any thoughts?

Sep 19, 2013
... from a laymen's intuitive perspective

any thoughts?

Yeah. Leave the thinking to experts who actually know stuff (and don't have to 'intuit'). Intuition sucks when it comes to science.

Sep 19, 2013
well I guess that settles it then .... only experts are allowed to ask the questions.

Sep 19, 2013
theory seems to often intuit connections and then testing confirms truth. please don't be an ass.

Sep 19, 2013
Oh hell... the earth farted.

Sep 19, 2013
Must be from one of those hundreds of thousands of invisible volcanoes that anti-Science Frauds are claiming pepper the earth's surface.

Sep 19, 2013
A straight question deserves a straight answer (I am surprised at Anti because he is usually polite until provoked).

Large solar eruptions do release vast amounts of energy (up to ~10^26 Joules), but even in an earth-directed blast very little of that actually couples to hits the earth's magnetic field (~10^16 Joules), and only part of that ends up in the core.

And earth's core is huge - ~1.7x10^24 kg, and it takes 450 Joules to heat a kg of iron by 1 degree. So even the full 10^16 joules would only heat it by about 0.000000000014 of a degree. Since the convection is driven by a temperature difference of thousands of degrees, this tiny increase does not make any noticeable difference to the convection.

Sep 19, 2013
Must be from one of those hundreds of thousands of invisible volcanoes that anti-Science Frauds are claiming pepper the earth's surface.

Thirty Thousand.

I calculated as few as thirty thousand volcanoes could do the trick.

We could call this theory, "20,000 'Leaks' Under the Sea".

Sep 20, 2013
only experts are allowed to ask the questions.

There is a difference between a guess (or a random jumble of disconnected things haphazardly thrown together - as in your 'theory') and an educated guess.

The difference is the education.

It's the differenc between:
"Unicorns are pretty, rainbows are pretty, therefore unicorns may cause rainbows...any thoughts?"
"I only observe rainbows when there is a light source and moisture. maybe they're connecte...let's make a test and find out"

Sep 20, 2013
thank you RealScience

Sep 20, 2013
Actually many laymen here are more educated, than so-called experts

But you may notice that those laymen haven't made any valuable contribution to human knowledge at all. So they're pretty much a waste of oxygen (from a scientific/human knowledge standpoint).
You may delude yourself into thinking your thoughts without work are worth anything. But don't think for a second that anyone shares your delusion.

Scientists are interested in stuff outside their specialization.
Curiosity is THE defining trait of a scientist, and there is no known mechanism that limits curiosity to just one field.
You will find that all scientists are interested in most anything - if you ever get up the courage to actually talk to one. (Which isn't all that hard: their e-mail addresses are on every paper they write)

The intellectual arrogance of experts may serve as one indicia of their professional blindness

They're not arrogant. They can just tell 'dumb' when it talks to them (like you).

Sep 21, 2013
@Anti -
I understand being annoyed at posters who repeatedly post the same drivel on thread after thread, often off topic, and arrogantly ignore all evidence presented against their their pet theories on the grounds that they know more than mainstream science.

In contrast chopsaw stated that he was a layman, his post was on topic, and only posted once. He presented a personal observation (and asked if others shared this observation), plus presented a hypothesis as to cause and effect, and asked for feedback.

Sep 23, 2013
Anti. Your arrogance on here does the scientific world no favours. You fail to recognise the question originally asked which illustrates your lack of understanding of human nature.
Personally it matters not a jot to me just how qualified you are. Your arrogant attitude goes a long way towards putting ordinary people off from asking what to them is both a reasonable question and at the same time knowing that it might make them sound like a jerk. But it takes courage to admit you don't know something. Especially on public forums and places like this.
About time people like you wound their necks in and stopped trying to be holier than thou towards the masses. Your not gods.
Besides us little people with no intelligence hold sway over you educated types. Or have you forgotten who deals with your shit?

Sep 23, 2013
Your arrogance on here does the scientific world no favours.

Since we're not in the science world here (but a comment section of a news aggregation site). So what?
Yeah. I rip into the occasional blockhead. But only if it IS a blockhead.
make them sound like a jerk.

Intentionally. If you want to do science then realize that this requires a modicum of perparation BEFORE asking (stupid) questions. Just to make sure they're not totally stupid. Science isn't home decoration.

Notice how I do answer most newcomers' questions (even if fraught with logical errors) reasonably, calmly, and politely.
But there is a difference between an honestly naive question based on some thought on the one hand and a dumbshit-throwing-together-of-buzzwords and calling it 'scientific enquiry' on the other.

One demands courtesy, the other demands a ding around the earhole to get the neurons to wake up.

Sep 23, 2013
@anti - this is one of those rare occasions where I disagree with you.

This is not a case where someone insists that mainstream science is wrong without even questioning whether it is instead their own interpretation or math that is wrong, and then ignoring people pointing out flaws in their reasoning or math, and then repeating the error endlessly and off-topic.

In this case the newcomer asked a question rather than making an assertion, and it was not repetitiously posted, and it was on topic. Furthermore with recent articles on volcanoes and even earthquakes (Ader, Wdowinski, etc.) being triggered (not caused) by weather, thinking that space weather might also have an influence is not totally unreasonable. And while the strength of solar flares is easy to find, finding the energy a flare dumps into earth's magnetic field was non-trivial.

Therefore I see chopsaw's post as an honest question that deserved an honest answer.

Nov 18, 2013
This will be as much fun as shooting fish in a barrel.

"'Utter, damned rot!' said the president of the prestigious American Philosophical Society.
"'If we are to believe [this] hypothesis, we must forget everything we have learned in the last 70 years and start all over again,' said another American scientist.
Anyone who 'valued his reputation for scientific sanity' would never dare support such a theory, said a British geologist."

Some of you will already recognize the quotes. Some of the rest of you may benefit from learning the context and the eventual outcome:


Please sign in to add a comment. Registration is free, and takes less than a minute. Read more