Featured Research

from universities, journals, and other organizations

Seismologists puzzle over largest deep earthquake ever recorded

Date:
September 19, 2013
Source:
University of California - Santa Cruz
Summary:
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, the intense pressure on the fault should inhibit the kind of rupture that took place.

The May 24, 2013 Mw 8.3 earthquake beneath the Sea of Okhotsk, Russia, occurred as a result of normal faulting at a depth of approximately 600 km (portion of USGS poster).
Credit: U.S. Geological Survey

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 earthquake. 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 transition zone between the upper mantle and lower mantle, from 400 to 700 kilometers below the surface. They result from stress in a deep subducted slab where one plate of 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 seismic stations 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."


Story Source:

The above story is based on materials provided by University of California - Santa Cruz. The original article was written by Tim Stephens. Note: Materials may be edited for content and length.


Journal Reference:

  1. L. Ye, T. Lay, H. Kanamori, K. D. Koper. Energy Release of the 2013 Mw 8.3 Sea of Okhotsk Earthquake and Deep Slab Stress Heterogeneity. Science, 2013; 341 (6152): 1380 DOI: 10.1126/science.1242032

Cite This Page:

University of California - Santa Cruz. "Seismologists puzzle over largest deep earthquake ever recorded." ScienceDaily. ScienceDaily, 19 September 2013. <www.sciencedaily.com/releases/2013/09/130919142152.htm>.
University of California - Santa Cruz. (2013, September 19). Seismologists puzzle over largest deep earthquake ever recorded. ScienceDaily. Retrieved September 19, 2014 from www.sciencedaily.com/releases/2013/09/130919142152.htm
University of California - Santa Cruz. "Seismologists puzzle over largest deep earthquake ever recorded." ScienceDaily. www.sciencedaily.com/releases/2013/09/130919142152.htm (accessed September 19, 2014).

Share This



More Earth & Climate News

Friday, September 19, 2014

Featured Research

from universities, journals, and other organizations


Featured Videos

from AP, Reuters, AFP, and other news services

Raw: Wildfires in CA Burn Forest Asunder

Raw: Wildfires in CA Burn Forest Asunder

AP (Sep. 18, 2014) An out-of-control Northern California wildfire has nearly 2,800 people from their homes as it continues to grow, authorities said Thursday. Authorities said a man has been arrested on suspicion of arson for starting the fire on Saturday. (Sept. 18) Video provided by AP
Powered by NewsLook.com
Raw: Elephant Undergoes Surgery in Tbilisi Zoo

Raw: Elephant Undergoes Surgery in Tbilisi Zoo

AP (Sep. 18, 2014) Grand the elephant has successfully undergone surgery to remove a portion of infected tusk at Tbilisi Zoo in Georgia. British veterinary surgeons used an electric drill to extract the infected piece. (Sept. 18) Video provided by AP
Powered by NewsLook.com
Raw: Scientists Examine Colossal Squid

Raw: Scientists Examine Colossal Squid

AP (Sep. 16, 2014) Squid experts in New Zealand thawed and examined an unusual catch on Tuesday: a colossal squid. It was captured in Antarctica's remote Ross Sea in December last year and has been frozen for eight months. (Sept. 16) Video provided by AP
Powered by NewsLook.com
Man Floats for 31 Hours in Gulf Waters

Man Floats for 31 Hours in Gulf Waters

AP (Sep. 16, 2014) A Texas man is lucky to be alive after he and three others floated for more than a day in the Gulf of Mexico when their boat sank during a fishing trip. (Sept. 16) Video provided by AP
Powered by NewsLook.com

Search ScienceDaily

Number of stories in archives: 140,361

Find with keyword(s):
Enter a keyword or phrase to search ScienceDaily for related topics and research stories.

Save/Print:
Share:

Breaking News:
from the past week

In Other News

... from NewsDaily.com

Science News

Health News

Environment News

Technology News



Save/Print:
Share:

Free Subscriptions


Get the latest science news with ScienceDaily's free email newsletters, updated daily and weekly. Or view hourly updated newsfeeds in your RSS reader:

Get Social & Mobile


Keep up to date with the latest news from ScienceDaily via social networks and mobile apps:

Have Feedback?


Tell us what you think of ScienceDaily -- we welcome both positive and negative comments. Have any problems using the site? Questions?
Mobile: iPhone Android Web
Follow: Facebook Twitter Google+
Subscribe: RSS Feeds Email Newsletters
Latest Headlines Health & Medicine Mind & Brain Space & Time Matter & Energy Computers & Math Plants & Animals Earth & Climate Fossils & Ruins