Slow earthquakes are non-violent fault slippage events that take hours or days instead of a few brutal seconds to minutes to release their potent energy. The researchers discuss their data in a study published the June 11, issue of Nature.
"From 2002 to 2007 we monitored deformation in eastern Taiwan using three highly sensitive borehole strainmeters installed 650 to 870 feet (200-270 meters) deep. These devices detect otherwise imperceptible movements and distortions of rock," explained coauthor Selwyn Sacks of Carnegie's Department of Terrestrial Magnetism. "We also measured atmospheric pressure changes, because they usually produce proportional changes in strain, which we can then remove."Taiwan has frequent typhoons in the second half of each year but is typhoon free during the first 4 months. During the five-year study period, the researchers, including lead author Chiching Liu (Academia Sinica, Taiwan), identified 20 slow earthquakes that each lasted from hours to more than a day. The scientists did not detect any slow events during the typhoon-free season. Eleven of the 20 slow earthquakes coincided with typhoons. Those 11 were also stronger and characterized by more complex waveforms than the other slow events.
How does the low pressure trigger the slow quakes? The typhoon reduces atmospheric pressure on land in this region, but does not affect conditions at the ocean bottom, because water moves into the area and equalizes pressure. The reduction in pressure above one side of an obliquely dipping fault tends to unclamp it. "This fault experiences more or less constant strain and stress buildup," said Linde. "If it's close to failure, the small perturbation due to the low pressure of the typhoon can push it over the failure limit; if there is no typhoon, stress will continue to accumulate until it fails without the need for a trigger."
"It's surprising that this area of the globe has had no great earthquakes and relatively few large earthquakes," Linde remarked. "By comparison, the Nankai Trough in southwestern Japan, has a plate convergence rate about 4 centimeters per year, and this causes a magnitude 8 earthquake every 100 to 150 years. But the activity in southern Taiwan comes from the convergence of same two plates, and there the Philippine Sea Plate pushes against the Eurasian Plate at a rate twice that for Nankai."
The researchers speculate that the reason devastating earthquakes are rare in eastern Taiwan is because the slow quakes act as valves, releasing the stress frequently along a small section of the fault, eliminating the situation where a long segment sustains continuous high stresses until it ruptures in a single great earthquake. The group is now expanding their instrumentation and monitoring for this research.
The Carnegie Institution for Science (www.CIW.edu) has been a pioneering force in basic scientific research since 1902. It is a private, nonprofit organization with six research departments throughout the U.S. Carnegie scientists are leaders in plant biology, developmental biology, astronomy, materials science, global ecology, and Earth and planetary science.
Alan Linde | EurekAlert!
New Study Will Help Find the Best Locations for Thermal Power Stations in Iceland
19.01.2017 | University of Gothenburg
Water - as the underlying driver of the Earth’s carbon cycle
17.01.2017 | Max-Planck-Institut für Biogeochemie
An important step towards a completely new experimental access to quantum physics has been made at University of Konstanz. The team of scientists headed by...
Yersiniae cause severe intestinal infections. Studies using Yersinia pseudotuberculosis as a model organism aim to elucidate the infection mechanisms of these...
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...
19.01.2017 | Event News
10.01.2017 | Event News
09.01.2017 | Event News
20.01.2017 | Awards Funding
20.01.2017 | Materials Sciences
20.01.2017 | Life Sciences