Forum for Science, Industry and Business

Sponsored by:     3M 
Search our Site:

 

Some large Pacific Northwest quakes could be limited in size by their location

14.11.2003


Large, deep earthquakes have shaken the central Puget Sound region several times in the last century, and nerves have been rattled even more often by less-powerful deep quakes. New University of Washington research suggests the magnitude of these temblors might depend on just where beneath the Earth’s surface they occur.



Events such as the 2001 Nisqually earthquake and large quakes in 1965 and 1949 happened in what is called the Wadati-Benioff zone, an area deep below the surface where the Juan de Fuca tectonic plate is sliding eastward beneath the North American plate. The two plates first meet on the ocean floor off the coast of Washington, Oregon and British Columbia.

If it turns out that such earthquakes are confined to the uppermost part of the Juan de Fuca plate, in its crustal layer, that means the magnitude of such quakes probably is limited to about 7, said Kenneth Creager, a University of Washington Earth and space sciences professor. However, the plate’s crust is only about 3 miles thick, and the cold mantle layer that lies just beneath is much thicker, so a quake that occurs in both layers, in theory, could reach a magnitude of 8, he said.


For a more-detailed examination than previously possible, new tools were devised to analyze data from an experiment called Seismic Hazards Investigations in Puget Sound, or SHIPS. Leiph Preston, now a post-doctoral researcher at the University of Nevada, Reno, created the tools as part of his doctoral research at the UW.

Preston is the lead author of a paper detailing the new analysis published in the Nov. 14 edition of the journal Science. Co-authors are Creager; Robert Crosson, also a UW Earth and space sciences professor; Thomas Brocher with the U.S. Geological Survey in Menlo Park, Calif.; and Anne Tréhu of Oregon State University. The work was funded by the USGS and the National Science Foundation.

In 1998, the SHIPS experiment measured airgun explosions in Puget Sound and the Strait of Juan de Fuca. The detonations generated seismic waves that rebounded from underground structures and then were measured by 200 seismic recorders to generate a subsurface picture.

The boundary between the crust and the mantle in the Juan de Fuca plate created a natural reflector for the sound waves, Preston said, which helped establish a precise location for the boundary. When the depths of various earthquakes were superimposed, it turned out those east of the Olympic Mountains, where the reflector’s depth reaches about 30 miles, occurred mainly in the Juan de Fuca plate’s crust. Quakes west of the Olympics, where the reflector is shallower, occur primarily below it in the plate’s mantle.

"The earthquakes and the reflector are so close to each other that it’s taken us five years to be confident of this interpretation," Creager said.

The crust is largely composed of basalt, but when the plate reaches a depth of about 30 miles the basalt sheds water and is transformed into a denser rock called eclogite.

"The fluids seem to be the key, as they provide the lubricant that allows the two sides of a fault to slip past each other to produce an earthquake," Creager said.

If such an earthquake occurs both in the crust and the mantle, thus allowing it to reach a greater magnitude, it would pose a bigger risk to the heavily populated Interstate 5 corridor west of the Cascades. A magnitude 8 earthquake releases 30 times more energy than a magnitude 7 event, and even though the Juan de Fuca plate goes deeper into the Earth as it moves to the east, it also gets closer to being directly beneath the population centers of western Washington.

The Nisqually earthquake in 2001, which occurred beneath the Nisqually River delta near Olympia, measured magnitude 6.8, while the 1949 earthquake, also near Olympia, measured 7.1. The 1965 earthquake between Seattle and Tacoma registered 6.5.

Western Washington also can encounter subduction zone earthquakes, which occur infrequently offshore where the two plates come together and could perhaps measure magnitude 9. There also are major faults, such as the Seattle fault, that typically produce much shallower quakes with more pronounced shaking, so a high magnitude could bring widespread damage.

The new understanding of the nature of earthquakes in the Wadati-Benioff zone means more work like the SHIPS experiment is needed farther south, "particularly in the area of the Nisqually delta, where we have experienced these large earthquakes," Crosson said. "That will help us to understand the effects of such earthquakes on the entire region."


For more information, contact Preston at 775-784-1684 or preston@ess.washington.edu; Creager at 206-685-2803 or kcc@ess.washington.edu; Crosson at 206-543-6505 or crosson@u.washington.edu; Brocher at 650-329-4737 or brocher@usgs.gov; or Tréhu at 541-737-2655 or trehu@coas.oregonstate.edu

Vince Stricherz | EurekAlert!
Further information:
http://www.washington.edu/

More articles from Earth Sciences:

nachricht Filling the gap: High-latitude volcanic eruptions also have global impact
20.11.2017 | Institute of Atmospheric Physics, Chinese Academy of Sciences

nachricht Antarctic landscape insights keep ice loss forecasts on the radar
20.11.2017 | University of Edinburgh

All articles from Earth Sciences >>>

The most recent press releases about innovation >>>

Die letzten 5 Focus-News des innovations-reports im Überblick:

Im Focus: Nanoparticles help with malaria diagnosis – new rapid test in development

The WHO reports an estimated 429,000 malaria deaths each year. The disease mostly affects tropical and subtropical regions and in particular the African continent. The Fraunhofer Institute for Silicate Research ISC teamed up with the Fraunhofer Institute for Molecular Biology and Applied Ecology IME and the Institute of Tropical Medicine at the University of Tübingen for a new test method to detect malaria parasites in blood. The idea of the research project “NanoFRET” is to develop a highly sensitive and reliable rapid diagnostic test so that patient treatment can begin as early as possible.

Malaria is caused by parasites transmitted by mosquito bite. The most dangerous form of malaria is malaria tropica. Left untreated, it is fatal in most cases....

Im Focus: A “cosmic snake” reveals the structure of remote galaxies

The formation of stars in distant galaxies is still largely unexplored. For the first time, astron-omers at the University of Geneva have now been able to closely observe a star system six billion light-years away. In doing so, they are confirming earlier simulations made by the University of Zurich. One special effect is made possible by the multiple reflections of images that run through the cosmos like a snake.

Today, astronomers have a pretty accurate idea of how stars were formed in the recent cosmic past. But do these laws also apply to older galaxies? For around a...

Im Focus: Visual intelligence is not the same as IQ

Just because someone is smart and well-motivated doesn't mean he or she can learn the visual skills needed to excel at tasks like matching fingerprints, interpreting medical X-rays, keeping track of aircraft on radar displays or forensic face matching.

That is the implication of a new study which shows for the first time that there is a broad range of differences in people's visual ability and that these...

Im Focus: Novel Nano-CT device creates high-resolution 3D-X-rays of tiny velvet worm legs

Computer Tomography (CT) is a standard procedure in hospitals, but so far, the technology has not been suitable for imaging extremely small objects. In PNAS, a team from the Technical University of Munich (TUM) describes a Nano-CT device that creates three-dimensional x-ray images at resolutions up to 100 nanometers. The first test application: Together with colleagues from the University of Kassel and Helmholtz-Zentrum Geesthacht the researchers analyzed the locomotory system of a velvet worm.

During a CT analysis, the object under investigation is x-rayed and a detector measures the respective amount of radiation absorbed from various angles....

Im Focus: Researchers Develop Data Bus for Quantum Computer

The quantum world is fragile; error correction codes are needed to protect the information stored in a quantum object from the deteriorating effects of noise. Quantum physicists in Innsbruck have developed a protocol to pass quantum information between differently encoded building blocks of a future quantum computer, such as processors and memories. Scientists may use this protocol in the future to build a data bus for quantum computers. The researchers have published their work in the journal Nature Communications.

Future quantum computers will be able to solve problems where conventional computers fail today. We are still far away from any large-scale implementation,...

All Focus news of the innovation-report >>>

Anzeige

Anzeige

Event News

Ecology Across Borders: International conference brings together 1,500 ecologists

15.11.2017 | Event News

Road into laboratory: Users discuss biaxial fatigue-testing for car and truck wheel

15.11.2017 | Event News

#Berlin5GWeek: The right network for Industry 4.0

30.10.2017 | Event News

 
Latest News

Previous evidence of water on mars now identified as grainflows

21.11.2017 | Physics and Astronomy

NASA's James Webb Space Telescope completes final cryogenic testing

21.11.2017 | Physics and Astronomy

New catalyst controls activation of a carbon-hydrogen bond

21.11.2017 | Life Sciences

VideoLinks
B2B-VideoLinks
More VideoLinks >>>