Subscribe free to our newsletters via your
. 24/7 Space News .




SHAKE AND BLOW
Seismologists puzzle over largest deep earthquake ever recorded
by Staff Writers
Santa Cruz CA (SPX) Sep 24, 2013


The world's largest recorded deep earthquake occurred on May 24, 2013, at a depth of 609 km in the subducting Pacific plate beneath the Sea of Okhotsk near Kamchatka, Russia, as shown in the schematic vertical cross-section above and on the map below. (Credit: diagram by L. Ye and T. Lay, map by Ye et al., Science).

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 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 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 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."

In addition to Ye and Lay, the coauthors of the paper include Hiroo Kanamori of the California Institute of Technology and Keith Koper of the University of Utah. This work was supported in part by the National Science Foundation (grant #EAR-1245717).

.


Related Links
University of California - Santa Cruz
Bringing Order To A World Of Disasters
When the Earth Quakes
A world of storm and tempest






Comment on this article via your Facebook, Yahoo, AOL, Hotmail login.

Share this article via these popular social media networks
del.icio.usdel.icio.us DiggDigg RedditReddit GoogleGoogle








SHAKE AND BLOW
Power outages, landslides after strong Guatemala quake
Guatemala City (AFP) Sept 07, 2013
Guatemala braced for more aftershocks Saturday, a day after a strong 6.5 magnitude earthquake struck the south of the country, leading to power outages and landslides. Officials said there were some two dozen aftershocks overnight, as they placed the nation on orange alert, one below the highest level red. The temblor caused cuts in power, interruptions in phone service and landslides, a ... read more


SHAKE AND BLOW
Watch Out for the Harvest Moon

Chang'e-3 lunar probe sent to launch site

Sixteen Tons of Moondust

Scientists say water on moon may have originated on Earth

SHAKE AND BLOW
Communications Tests Go the Distance for MAVEN

Curiosity Rover Detects No Methane On Mars

Robotic Arm Goes to Work on Rock Target

India unveils Mars mission spacecraft

SHAKE AND BLOW
Iran to send second monkey into space

Voyager's departure from the heliosphere

NASA study is enough to make a person want to stay in bed

Voyager 1 spacecraft reaches interstellar space

SHAKE AND BLOW
China's space station to open for foreign peers

Last Days for Tiangong

China civilian technology satellites put into use

China to launch lunar lander by end of year: media

SHAKE AND BLOW
Cygnus arrival at ISS delayed by at least 2 days: NASA

ISS Orbit to Be Raised Ahead of Crew Arrival

ISS Releases a White Stork and Awaits a Swan

Three astronauts back on Earth from ISS: mission control

SHAKE AND BLOW
Problems with Proton booster fixed

Decontamination continues at Baikonur after Proton abortive launc

Russia launches three communication satellites

Arianespace remains the global launch services leader

SHAKE AND BLOW
ESA selects SSTL to design Exoplanet satellite mission

Coldest Brown Dwarfs Blur Lines between Stars and Planets

NASA-funded Program Helps Amateur Astronomers Detect Alien Worlds

Observations strongly suggest distant super-Earth has water atmosphere

SHAKE AND BLOW
New Model Should Expedite Development of Temperature-Stable Nano-Alloys

Balkans gold rush prompts pollution fears

Environmentally friendly cement is stronger than ordinary cement

X-ray science taps bug biology to design better materials and reduce pollution




The content herein, unless otherwise known to be public domain, are Copyright 1995-2014 - Space Media Network. AFP, UPI and IANS news wire stories are copyright Agence France-Presse, United Press International and Indo-Asia News Service. ESA Portal Reports are copyright European Space Agency. All NASA sourced material is public domain. Additional copyrights may apply in whole or part to other bona fide parties. Advertising does not imply endorsement,agreement or approval of any opinions, statements or information provided by Space Media Network on any Web page published or hosted by Space Media Network. Privacy Statement