Forum for Science, Industry and Business

Sponsored by:     3M 
Search our Site:

 

Rising tides intensify non-volcanic tremor in Earth's crust

27.11.2007
For more than a decade geoscientists have detected what amount to ultra-slow-motion earthquakes under Western Washington and British Columbia on a regular basis, about every 14 months. Such episodic tremor-and-slip events typically last two to three weeks and can release as much energy as a large earthquake, though they are not felt and cause no damage.

Now University of Washington researchers have found evidence that these slow-slip events are actually affected by the rise and fall of ocean tides.

"There has been some previous evidence of the tidal effect, but the detail is not as great as what we have found," said Justin Rubinstein, a UW postdoctoral researcher in Earth and space sciences.

And while previous research turned up suggestions of a tidal pulse at 12.4 hours, this is the first time that a second pulse, somewhat more difficult to identify, emerged in the evidence at intervals of 24 to 25 hours, he said.

Rubinstein is lead author of a paper that provides details of the findings, published Nov. 22 in Science Express, the online edition of the journal Science. Co-authors are Mario La Rocca of the Istituto Nazionale di Geofisica e Vulcanologia in Italy, and John Vidale, Kenneth Creager and Aaron Wech of the UW.

The most recent tremor-and-slip events in Washington and British Columbia took place in July 2004, September 2005 and January 2007. Before each, researchers deployed seismic arrays, each containing five to 11 separate seismic monitoring stations, to collect more accurate information about the location and nature of the tremors. Four of the arrays were placed on the Olympic Peninsula in Washington and the fifth was on Vancouver Island in British Columbia.

The arrays recorded clear twice-a-day pulsing in the 2004 and 2007 episodes, and similar pulsing occurred in 2005 but was not as clearly identified. The likely source from tidal stresses, the researchers said, would be roughly once- and twice-a-day pulses from the gravitational influence of the sun and moon. The clearest tidal pulse at 12.4 hours coincided with a peak in lunar forcing, while the pulse at 24 to 25 hours was linked to peaks in both lunar and solar influences.

The rising tide appeared to increase the tremor by a factor of 30 percent, though the Earth distortion still was so small that it was undetectable without instruments, said Vidale, a UW professor of Earth and space sciences and director of the Pacific Northwest Seismograph Network.

"We expected that the added water of a rising tide would clamp down on the tremor, but it seems to have had the opposite effect. It's fair to say that we don't understand it," Vidale said.

"Earthquakes don't behave this way," he added. "Most don't care whether the tide is high or low."

The researchers were careful to rule out noise that might have come from human activity. For instance, one of the arrays was near a logging camp and another was near a mine.

"It's pretty impressive how strong a signal those activities can create," Rubinstein said, adding that the slow-slip pulses were recorded when those human activities were at a minimum.

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

All articles from Earth Sciences >>>

The most recent press releases about innovation >>>

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

Im Focus: A Challenging European Research Project to Develop New Tiny Microscopes

The Institute of Semiconductor Technology and the Institute of Physical and Theoretical Chemistry, both members of the Laboratory for Emerging Nanometrology (LENA), at Technische Universität Braunschweig are partners in a new European research project entitled ChipScope, which aims to develop a completely new and extremely small optical microscope capable of observing the interior of living cells in real time. A consortium of 7 partners from 5 countries will tackle this issue with very ambitious objectives during a four-year research program.

To demonstrate the usefulness of this new scientific tool, at the end of the project the developed chip-sized microscope will be used to observe in real-time...

Im Focus: Giant Magnetic Fields in the Universe

Astronomers from Bonn and Tautenburg in Thuringia (Germany) used the 100-m radio telescope at Effelsberg to observe several galaxy clusters. At the edges of these large accumulations of dark matter, stellar systems (galaxies), hot gas, and charged particles, they found magnetic fields that are exceptionally ordered over distances of many million light years. This makes them the most extended magnetic fields in the universe known so far.

The results will be published on March 22 in the journal „Astronomy & Astrophysics“.

Galaxy clusters are the largest gravitationally bound structures in the universe. With a typical extent of about 10 million light years, i.e. 100 times the...

Im Focus: Tracing down linear ubiquitination

Researchers at the Goethe University Frankfurt, together with partners from the University of Tübingen in Germany and Queen Mary University as well as Francis Crick Institute from London (UK) have developed a novel technology to decipher the secret ubiquitin code.

Ubiquitin is a small protein that can be linked to other cellular proteins, thereby controlling and modulating their functions. The attachment occurs in many...

Im Focus: Perovskite edges can be tuned for optoelectronic performance

Layered 2D material improves efficiency for solar cells and LEDs

In the eternal search for next generation high-efficiency solar cells and LEDs, scientists at Los Alamos National Laboratory and their partners are creating...

Im Focus: Polymer-coated silicon nanosheets as alternative to graphene: A perfect team for nanoelectronics

Silicon nanosheets are thin, two-dimensional layers with exceptional optoelectronic properties very similar to those of graphene. Albeit, the nanosheets are less stable. Now researchers at the Technical University of Munich (TUM) have, for the first time ever, produced a composite material combining silicon nanosheets and a polymer that is both UV-resistant and easy to process. This brings the scientists a significant step closer to industrial applications like flexible displays and photosensors.

Silicon nanosheets are thin, two-dimensional layers with exceptional optoelectronic properties very similar to those of graphene. Albeit, the nanosheets are...

All Focus news of the innovation-report >>>

Anzeige

Anzeige

Event News

International Land Use Symposium ILUS 2017: Call for Abstracts and Registration open

20.03.2017 | Event News

CONNECT 2017: International congress on connective tissue

14.03.2017 | Event News

ICTM Conference: Turbine Construction between Big Data and Additive Manufacturing

07.03.2017 | Event News

 
Latest News

NASA laser communications to provide Orion faster connections

30.03.2017 | Physics and Astronomy

Reusable carbon nanotubes could be the water filter of the future, says RIT study

30.03.2017 | Studies and Analyses

Unique genome architectures after fertilisation in single-cell embryos

30.03.2017 | Life Sciences

VideoLinks
B2B-VideoLinks
More VideoLinks >>>