Forum for Science, Industry and Business

Sponsored by:     3M 
Search our Site:

 

‘Array of Arrays’ Coaxing Secrets from Unfelt Seismic Tremor Events

15.12.2010
Every 15 months or so, an unfelt earthquake occurs in western Washington and travels northward to Canada’s Vancouver Island. The episode typically releases as much energy as a magnitude 6.5 earthquake, but it does so gradually over a month.

New technology is letting University of Washington researchers get a much better picture of how these episodic tremor events relate to potentially catastrophic earthquakes, perhaps as powerful as magnitude 9, that occur every 300 to 500 years in the Cascadia subduction zone in western Washington, Oregon and British Columbia.

“Depending on where the tremor is, a different part of the fault is being loaded,” said Abhijit Ghosh, a UW doctoral student in Earth and space sciences, who is presenting the most recent findings Monday (Dec. 13) at the annual meeting of the American Geophysical Union in San Francisco.

Scientists discovered episodic tremor about a decade ago and have been trying to understand how it figures in the seismic hierarchy of the earthquake-prone Pacific Northwest. In 2008 on Washington’s Olympic Peninsula, UW scientists deployed an array of 80 seismic sensors that act something like a radio antenna, except that instead of bringing in distant radio waves it collects signals from tremor events. Now there are eight such arrays, each armed with 20 to 30 sensors, a complex the scientists call the “array of arrays.”

It was known that tremor events generally start near Olympia, Wash., and march slowly northward on the Olympic Peninsula, eventually reaching Canada’s Vancouver Island and running their course in several weeks.

But Ghosh has found the tremor movement to be far more complex. The source of the tremor generates streaks that travel 60 miles per hour back and forth along a southwest-northeast track. Several hours of this activity produces what shows up as bands of tremor that steadily migrate northward at a much slower speed, about 6 miles per day.

The effect is similar to someone painting a wall, with the wall representing the area where the tremor occurs and paint representing tremor streaks. Eventually the brush strokes will cover the wall.

The arrays are producing enough data for scientists to locate the precise latitude and longitude where a signal originates, Ghosh said, but more work must be done to determine precise depths. It could be that the signal comes from the same depth, about 25 miles, as the subduction fault zone, but that is unclear.

“Because the signal is very different from our garden variety earthquakes, we need new techniques to determine the source of the signal, and this is one step toward that,” Ghosh said. “With the array of arrays we should be able to see a greater quantity of clear signal, and we do. We see more tremor – way more tremor – than with conventional methods.”

Researchers have known for several years that these tremor events add to the fault stress in the Cascadia subduction zone, where the Juan de Fuca tectonic plate dives beneath the North American plate that is directly under the most populous areas of Washington, Oregon and British Columbia. The last great Cascadia subduction zone earthquake, estimated at magnitude 9, occurred in January 1700 and generated a tsunami that traveled to Japan.

The arrays are beginning to produce a better understanding of how tremor events are related to the Cascadia fault zone. For example, the southwest-northeast angle of the tremor streaks and bands matches almost exactly the angle, about 54 degrees, at which the Juan de Fuca plate meets the North American plate.

“We have already seen different types of tremor migration in Cascadia, and there might be even more,” Ghosh said. “With high-precision locating technology, we are getting a clearer picture.”

For more information, contact Ghosh at aghosh.earth@gmail.com or 404-667-7470, or John Vidale, UW professor of Earth and space sciences, at vidale@uw.edu or 310-210-2131.

Vince Stricherz | Newswise Science News
Further information:
http://www.uw.edu

More articles from Earth Sciences:

nachricht How do megacities impact coastal seas? Searching for evidence in Chinese marginal seas
11.12.2017 | Leibniz-Institut für Ostseeforschung Warnemünde

nachricht What makes corals sick?
11.12.2017 | Leibniz-Zentrum für Marine Tropenforschung (ZMT)

All articles from Earth Sciences >>>

The most recent press releases about innovation >>>

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

Im Focus: Scientists channel graphene to understand filtration and ion transport into cells

Tiny pores at a cell's entryway act as miniature bouncers, letting in some electrically charged atoms--ions--but blocking others. Operating as exquisitely sensitive filters, these "ion channels" play a critical role in biological functions such as muscle contraction and the firing of brain cells.

To rapidly transport the right ions through the cell membrane, the tiny channels rely on a complex interplay between the ions and surrounding molecules,...

Im Focus: Towards data storage at the single molecule level

The miniaturization of the current technology of storage media is hindered by fundamental limits of quantum mechanics. A new approach consists in using so-called spin-crossover molecules as the smallest possible storage unit. Similar to normal hard drives, these special molecules can save information via their magnetic state. A research team from Kiel University has now managed to successfully place a new class of spin-crossover molecules onto a surface and to improve the molecule’s storage capacity. The storage density of conventional hard drives could therefore theoretically be increased by more than one hundred fold. The study has been published in the scientific journal Nano Letters.

Over the past few years, the building blocks of storage media have gotten ever smaller. But further miniaturization of the current technology is hindered by...

Im Focus: Successful Mechanical Testing of Nanowires

With innovative experiments, researchers at the Helmholtz-Zentrums Geesthacht and the Technical University Hamburg unravel why tiny metallic structures are extremely strong

Light-weight and simultaneously strong – porous metallic nanomaterials promise interesting applications as, for instance, for future aeroplanes with enhanced...

Im Focus: Virtual Reality for Bacteria

An interdisciplinary group of researchers interfaced individual bacteria with a computer to build a hybrid bio-digital circuit - Study published in Nature Communications

Scientists at the Institute of Science and Technology Austria (IST Austria) have managed to control the behavior of individual bacteria by connecting them to a...

Im Focus: A space-time sensor for light-matter interactions

Physicists in the Laboratory for Attosecond Physics (run jointly by LMU Munich and the Max Planck Institute for Quantum Optics) have developed an attosecond electron microscope that allows them to visualize the dispersion of light in time and space, and observe the motions of electrons in atoms.

The most basic of all physical interactions in nature is that between light and matter. This interaction takes place in attosecond times (i.e. billionths of a...

All Focus news of the innovation-report >>>

Anzeige

Anzeige

Event News

See, understand and experience the work of the future

11.12.2017 | Event News

Innovative strategies to tackle parasitic worms

08.12.2017 | Event News

AKL’18: The opportunities and challenges of digitalization in the laser industry

07.12.2017 | Event News

 
Latest News

Midwife and signpost for photons

11.12.2017 | Physics and Astronomy

How do megacities impact coastal seas? Searching for evidence in Chinese marginal seas

11.12.2017 | Earth Sciences

PhoxTroT: Optical Interconnect Technologies Revolutionized Data Centers and HPC Systems

11.12.2017 | Information Technology

VideoLinks
B2B-VideoLinks
More VideoLinks >>>