New research has found evidence of tremors along non-subduction zone faults in seven California locations. The tremors immediately followed the magnitude 7.8 Denali earthquake in Alaska on Nov. 3, 2002 and are linked to that quake even though they are as much as 2,400 miles from its epicenter.
"This suggests there is a much greater variety of ways that faults store up stress and release it," said Joan Gomberg, an affiliate professor of Earth and space sciences at the University of Washington and a research scientist with the U.S. Geological Survey in Seattle.
The tremors began within an hour of the Denali earthquake, and their signal was observed as high-frequency pulses among the lower-frequency signals from the main earthquake. The seven distinct areas, stretching from north of San Francisco to southeast of Los Angeles, are near Napa Valley, San Jose, San Juan Bautista, Simi Valley, Hemet and two sites near Parkfield.
Five of the sources are close to or on dominant strike-slip faults – the San Andreas, San Jacinto and Calaveras faults – in which two blocks of the Earth's crust slide past each other horizontally. The scientists believe the other two tremor sources, in Napa Valley and Simi Valley, are likely on more minor faults.
"All seven of these were set off by the strong passing waves from Denali," Gomberg said.
The research is being published Nov. 22 in Science Express, the online edition of the journal Science. Co-authors are Justin Rubinstein, Kenneth Creager, John Vidale and Paul Bodin of the UW and Zhigang Peng of the Georgia Institute of Technology.
Tremor episodes have been observed near volcanoes for many years, and more recently they have been seen around subduction zones such as Cascadia, 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 over days or weeks, rather than seconds.
The scientists examined all available recordings of Denali earthquake waves from seismic stations throughout California and were able to identify high-frequency waves that pulsed with passing surface waves. The researchers determined the high-frequency waves were not part of the Denali quake itself, nor were they caused by any smaller nearby earthquakes.
Previous studies have indicated a possible link between tremor or slow-slip events and fluids and high temperatures within tectonic plates. So the scientists specifically examined data from stations close to two geothermal fields in California, but they found no apparent signal for tremor.
"It was the opposite of what we expected," Gomberg said.
The lack of tremor in these areas triggered by the Denali earthquake probably means that while fluids or high temperatures might be necessary for a tremor, they are not sufficient by themselves to produce tremor, the scientists concluded.
Gomberg said it is possible that tremor events occur at the edges of zones where two tectonic plates are locked together, gradually building energy toward a major earthquake. If that is the case, she said, the research could help scientists map the locked zones and develop a clearer picture of a particular region's earthquake risk.
"This has opened new questions, and perhaps it has provided the start of some answers, about what makes faults move and the ways that they move," Gomberg said.
"Such research has made it worth it to put in all the recording equipment that we have measuring seismic events. You never know what you are going to learn."
Vince Stricherz | EurekAlert!
As sea level rises, much of Honolulu and Waikiki vulnerable to groundwater inundation
29.03.2017 | University of Hawaii at Manoa
Researchers discover dust plays prominent role in nutrients of mountain forest ecoystems
29.03.2017 | University of Wyoming
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...
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...
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...
In the eternal search for next generation high-efficiency solar cells and LEDs, scientists at Los Alamos National Laboratory and their partners are creating...
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...
20.03.2017 | Event News
14.03.2017 | Event News
07.03.2017 | Event News
30.03.2017 | Health and Medicine
30.03.2017 | Health and Medicine
30.03.2017 | Medical Engineering