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 email@example.com or 404-667-7470, or John Vidale, UW professor of Earth and space sciences, at firstname.lastname@example.org or 310-210-2131.
Vince Stricherz | Newswise Science News
Water - as the underlying driver of the Earth’s carbon cycle
17.01.2017 | Max-Planck-Institut für Biogeochemie
Modeling magma to find copper
13.01.2017 | Université de Genève
Researchers from the University of Hamburg in Germany, in collaboration with colleagues from the University of Aarhus in Denmark, have synthesized a new superconducting material by growing a few layers of an antiferromagnetic transition-metal chalcogenide on a bismuth-based topological insulator, both being non-superconducting materials.
While superconductivity and magnetism are generally believed to be mutually exclusive, surprisingly, in this new material, superconducting correlations...
Laser-driving of semimetals allows creating novel quasiparticle states within condensed matter systems and switching between different states on ultrafast time scales
Studying properties of fundamental particles in condensed matter systems is a promising approach to quantum field theory. Quasiparticles offer the opportunity...
Among the general public, solar thermal energy is currently associated with dark blue, rectangular collectors on building roofs. Technologies are needed for aesthetically high quality architecture which offer the architect more room for manoeuvre when it comes to low- and plus-energy buildings. With the “ArKol” project, researchers at Fraunhofer ISE together with partners are currently developing two façade collectors for solar thermal energy generation, which permit a high degree of design flexibility: a strip collector for opaque façade sections and a solar thermal blind for transparent sections. The current state of the two developments will be presented at the BAU 2017 trade fair.
As part of the “ArKol – development of architecturally highly integrated façade collectors with heat pipes” project, Fraunhofer ISE together with its partners...
At TU Wien, an alternative for resource intensive formwork for the construction of concrete domes was developed. It is now used in a test dome for the Austrian Federal Railways Infrastructure (ÖBB Infrastruktur).
Concrete shells are efficient structures, but not very resource efficient. The formwork for the construction of concrete domes alone requires a high amount of...
Many pathogens use certain sugar compounds from their host to help conceal themselves against the immune system. Scientists at the University of Bonn have now, in cooperation with researchers at the University of York in the United Kingdom, analyzed the dynamics of a bacterial molecule that is involved in this process. They demonstrate that the protein grabs onto the sugar molecule with a Pac Man-like chewing motion and holds it until it can be used. Their results could help design therapeutics that could make the protein poorer at grabbing and holding and hence compromise the pathogen in the host. The study has now been published in “Biophysical Journal”.
The cells of the mouth, nose and intestinal mucosa produce large quantities of a chemical called sialic acid. Many bacteria possess a special transport system...
10.01.2017 | Event News
09.01.2017 | Event News
05.01.2017 | Event News
17.01.2017 | Earth Sciences
17.01.2017 | Materials Sciences
17.01.2017 | Architecture and Construction