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!
Global study of world's beaches shows threat to protected areas
19.07.2018 | NASA/Goddard Space Flight Center
NSF-supported researchers to present new results on hurricanes and other extreme events
19.07.2018 | National Science Foundation
A new manufacturing technique uses a process similar to newspaper printing to form smoother and more flexible metals for making ultrafast electronic devices.
The low-cost process, developed by Purdue University researchers, combines tools already used in industry for manufacturing metals on a large scale, but uses...
For the first time ever, scientists have determined the cosmic origin of highest-energy neutrinos. A research group led by IceCube scientist Elisa Resconi, spokesperson of the Collaborative Research Center SFB1258 at the Technical University of Munich (TUM), provides an important piece of evidence that the particles detected by the IceCube neutrino telescope at the South Pole originate from a galaxy four billion light-years away from Earth.
To rule out other origins with certainty, the team led by neutrino physicist Elisa Resconi from the Technical University of Munich and multi-wavelength...
For the first time a team of researchers have discovered two different phases of magnetic skyrmions in a single material. Physicists of the Technical Universities of Munich and Dresden and the University of Cologne can now better study and understand the properties of these magnetic structures, which are important for both basic research and applications.
Whirlpools are an everyday experience in a bath tub: When the water is drained a circular vortex is formed. Typically, such whirls are rather stable. Similar...
Physicists working with Roland Wester at the University of Innsbruck have investigated if and how chemical reactions can be influenced by targeted vibrational excitation of the reactants. They were able to demonstrate that excitation with a laser beam does not affect the efficiency of a chemical exchange reaction and that the excited molecular group acts only as a spectator in the reaction.
A frequently used reaction in organic chemistry is nucleophilic substitution. It plays, for example, an important role in in the synthesis of new chemical...
Optical spectroscopy allows investigating the energy structure and dynamic properties of complex quantum systems. Researchers from the University of Würzburg present two new approaches of coherent two-dimensional spectroscopy.
"Put an excitation into the system and observe how it evolves." According to physicist Professor Tobias Brixner, this is the credo of optical spectroscopy....
13.07.2018 | Event News
12.07.2018 | Event News
03.07.2018 | Event News
20.07.2018 | Power and Electrical Engineering
20.07.2018 | Information Technology
20.07.2018 | Materials Sciences