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 Turbulence creates ice in clouds
08.11.2019 | Leibniz-Institut für Troposphärenforschung e. V.

nachricht Manganese nodules: project on environmental impact during deep sea mining
08.11.2019 | Jacobs University Bremen gGmbH

All articles from Earth Sciences >>>

The most recent press releases about innovation >>>

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

Im Focus: New opportunities in additive manufacturing presented

Fraunhofer IFAM Dresden demonstrates manufacturing of copper components

The Fraunhofer Institute for Manufacturing Technology and Advanced Materials IFAM in Dresden has succeeded in using Selective Electron Beam Melting (SEBM) to...

Im Focus: New Pitt research finds carbon nanotubes show a love/hate relationship with water

Carbon nanotubes (CNTs) are valuable for a wide variety of applications. Made of graphene sheets rolled into tubes 10,000 times smaller than a human hair, CNTs have an exceptional strength-to-mass ratio and excellent thermal and electrical properties. These features make them ideal for a range of applications, including supercapacitors, interconnects, adhesives, particle trapping and structural color.

New research reveals even more potential for CNTs: as a coating, they can both repel and hold water in place, a useful property for applications like printing,...

Im Focus: Magnets for the second dimension

If you've ever tried to put several really strong, small cube magnets right next to each other on a magnetic board, you'll know that you just can't do it. What happens is that the magnets always arrange themselves in a column sticking out vertically from the magnetic board. Moreover, it's almost impossible to join several rows of these magnets together to form a flat surface. That's because magnets are dipolar. Equal poles repel each other, with the north pole of one magnet always attaching itself to the south pole of another and vice versa. This explains why they form a column with all the magnets aligned the same way.

Now, scientists at ETH Zurich have managed to create magnetic building blocks in the shape of cubes that - for the first time ever - can be joined together to...

Im Focus: A new quantum data classification protocol brings us nearer to a future 'quantum internet'

The algorithm represents a first step in the automated learning of quantum information networks

Quantum-based communication and computation technologies promise unprecedented applications, such as unconditionally secure communications, ultra-precise...

Im Focus: Distorted Atoms

In two experiments performed at the free-electron laser FLASH in Hamburg a cooperation led by physicists from the Heidelberg Max Planck Institute for Nuclear physics (MPIK) demonstrated strongly-driven nonlinear interaction of ultrashort extreme-ultraviolet (XUV) laser pulses with atoms and ions. The powerful excitation of an electron pair in helium was found to compete with the ultrafast decay, which temporarily may even lead to population inversion. Resonant transitions in doubly charged neon ions were shifted in energy, and observed by XUV-XUV pump-probe transient absorption spectroscopy.

An international team led by physicists from the MPIK reports on new results for efficient two-electron excitations in helium driven by strong and ultrashort...

All Focus news of the innovation-report >>>

Anzeige

Anzeige

VideoLinks
Industry & Economy
Event News

High entropy alloys for hot turbines and tireless metal-forming presses

05.11.2019 | Event News

Smart lasers open up new applications and are the “tool of choice” in digitalization

30.10.2019 | Event News

International Symposium on Functional Materials for Electrolysis, Fuel Cells and Metal-Air Batteries

02.10.2019 | Event News

 
Latest News

Theoretical tubulanes inspire ultrahard polymers

14.11.2019 | Materials Sciences

Can 'smart toilets' be the next health data wellspring?

14.11.2019 | Health and Medicine

New spin directions in pyrite an encouraging sign for future spintronics

14.11.2019 | Materials Sciences

VideoLinks
Science & Research
Overview of more VideoLinks >>>