Forum for Science, Industry and Business

Sponsored by:     3M 
Search our Site:

 

Alaskan earthquake in 2002 set off tremors on Vancouver Island

02.08.2007
Perhaps it was just a matter of sympathy, but tremors rippled the landscape of Vancouver Island, the westernmost part of British Columbia, in 2002 during a major Alaskan earthquake. Geoscientists at the University of Washington have found clear evidence that the two events were related.

Tremor episodes have long been observed near volcanoes and more recently around subduction zones, regions where the Earth's tectonic plates are shifting so that one slides beneath another. Tremors in subduction zones are associated with slow-slip events in which energy equivalent to a moderate-sized earthquake is released in days or weeks, rather than seconds.

Now researchers studying seismograph records have pinpointed five tremor bursts on Vancouver Island on Nov. 3, 2002, the result of a magnitude 7.8 earthquake on the Denali fault in the heart of Alaska.

As surface waves, called Love waves, shook Vancouver Island they triggered tremors underneath the island in the subduction zone where the Explorer tectonic plate slides beneath the North American plate. The tremors were measured by seismometers along roughly the northern two-thirds of the island.

"What we found is that when the waves pushed the North American plate to the southwest, the tremor episode turned on and when the motion reversed it turned off," said Justin Rubinstein, a UW postdoctoral researcher in Earth and space sciences and lead author of a paper describing the work published in the Aug. 2 edition of Nature.

Though the Denali quake was mostly felt in Alaska, its effects were apparent thousands of miles away. It sloshed lakes from Seattle to Louisiana, muddied wells as far east as Pennsylvania and triggered small earthquakes in seismic zones across the Western United States.

Still, finding evidence of tremors on Vancouver Island was unusual.

"A few people have seen tremor episodes triggered by earthquakes, but not as clearly as we have. This is by far the clearest and easiest to interpret," said co-author John Vidale, a UW professor of Earth and space sciences and director of the Pacific Northwest Seismic Network.

"This shows us it's just like a regular fault – you add stress and it slips," Vidale said. "It's like regular faulting but on a different time scale."

Other authors are Joan Gomberg of the U.S. Geological Survey in Seattle and UW researchers Paul Bodin, Kenneth Creager and Stephen Malone.

An earthquake typically will appear suddenly on a seismograph, while the much more subtle ground motion from a tremor burst gradually emerges from the background noise and then fades again, Rubinstein said.

By comparison, tremors typically produce the strongest seismic signals in a slow-slip event, in which seismic energy is released very gradually during periods as long as three weeks.

In this case, the authors suggest that the force of the Love waves induced slow slip on the interface between the North American and Explorer tectonic plates near Vancouver Island and triggered the tremor bursts, each lasting about 15 seconds.

"That made it easier for us to observe because there were these five distinct bursts," Rubinstein said. "Normally you are not going to feel these tremors. The shaking in the tremors we observed was 1,000 times smaller than the surface waves from the earthquake."

Being able to spot the tremors was largely a matter of distance and timing, Vidale said.

"We were able to separate the tremor signal from that of the distant earthquake because the surface waves had traveled more than 1,200 miles, losing the high-frequency vibrations that would have masked the high-frequency tremor vibrations," Vidale said.

While the tremors were recorded a great distance from the rupture that triggered the Denali earthquake, the scientists suggest the same process could occur closer to the fault and might actually be important in the rupture process.

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

More articles from Earth Sciences:

nachricht Predicting unpredictability: Information theory offers new way to read ice cores
07.12.2016 | Santa Fe Institute

nachricht Sea ice hit record lows in November
07.12.2016 | University of Colorado at Boulder

All articles from Earth Sciences >>>

The most recent press releases about innovation >>>

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

Im Focus: Significantly more productivity in USP lasers

In recent years, lasers with ultrashort pulses (USP) down to the femtosecond range have become established on an industrial scale. They could advance some applications with the much-lauded “cold ablation” – if that meant they would then achieve more throughput. A new generation of process engineering that will address this issue in particular will be discussed at the “4th UKP Workshop – Ultrafast Laser Technology” in April 2017.

Even back in the 1990s, scientists were comparing materials processing with nanosecond, picosecond and femtosesecond pulses. The result was surprising:...

Im Focus: Shape matters when light meets atom

Mapping the interaction of a single atom with a single photon may inform design of quantum devices

Have you ever wondered how you see the world? Vision is about photons of light, which are packets of energy, interacting with the atoms or molecules in what...

Im Focus: Novel silicon etching technique crafts 3-D gradient refractive index micro-optics

A multi-institutional research collaboration has created a novel approach for fabricating three-dimensional micro-optics through the shape-defined formation of porous silicon (PSi), with broad impacts in integrated optoelectronics, imaging, and photovoltaics.

Working with colleagues at Stanford and The Dow Chemical Company, researchers at the University of Illinois at Urbana-Champaign fabricated 3-D birefringent...

Im Focus: Quantum Particles Form Droplets

In experiments with magnetic atoms conducted at extremely low temperatures, scientists have demonstrated a unique phase of matter: The atoms form a new type of quantum liquid or quantum droplet state. These so called quantum droplets may preserve their form in absence of external confinement because of quantum effects. The joint team of experimental physicists from Innsbruck and theoretical physicists from Hannover report on their findings in the journal Physical Review X.

“Our Quantum droplets are in the gas phase but they still drop like a rock,” explains experimental physicist Francesca Ferlaino when talking about the...

Im Focus: MADMAX: Max Planck Institute for Physics takes up axion research

The Max Planck Institute for Physics (MPP) is opening up a new research field. A workshop from November 21 - 22, 2016 will mark the start of activities for an innovative axion experiment. Axions are still only purely hypothetical particles. Their detection could solve two fundamental problems in particle physics: What dark matter consists of and why it has not yet been possible to directly observe a CP violation for the strong interaction.

The “MADMAX” project is the MPP’s commitment to axion research. Axions are so far only a theoretical prediction and are difficult to detect: on the one hand,...

All Focus news of the innovation-report >>>

Anzeige

Anzeige

Event News

ICTM Conference 2017: Production technology for turbomachine manufacturing of the future

16.11.2016 | Event News

Innovation Day Laser Technology – Laser Additive Manufacturing

01.11.2016 | Event News

#IC2S2: When Social Science meets Computer Science - GESIS will host the IC2S2 conference 2017

14.10.2016 | Event News

 
Latest News

Scientists track chemical and structural evolution of catalytic nanoparticles in 3-D

08.12.2016 | Materials Sciences

Decoding cement's shape promises greener concrete

08.12.2016 | Materials Sciences

Will Earth still exist 5 billion years from now?

08.12.2016 | Physics and Astronomy

VideoLinks
B2B-VideoLinks
More VideoLinks >>>