Instruments placed on seafloor off the coast of Japan lead to new insight
Find related stories on NSF's geosciences risk and resilience interest area.
Understanding "slow-slip" earthquakes on the seafloor -- seismic events that occur over a period of days or weeks -- is giving researchers new insights into undersea earthquakes and the subsequent creation of tsunamis. Through an ocean discovery program supported by the National Science Foundation (NSF), scientists are studying the seafloor off the coast of Japan. The region could provide vital clues.
Assembly of pressure sensors to be installed 8,202 feet beneath the ocean surface.
Credit: Achim Kopf
Two tectonic plates, the Pacific Plate and the Eurasian Plate, meet there. In this ocean trench zone, the Pacific plate slides beneath the Eurasian plate. Such subduction zones are often associated with large earthquakes.
"This area is the shallowest part of the plate boundary system," said Demian Saffer, a geoscientist at Penn State University. "If this region near the ocean trench slips in an earthquake, it has the potential to generate a large tsunami."
Saffer and Eiichiro Araki, senior research scientist at the Japan Agency for Marine-Earth Science and Technology, published the results of their investigations of the plate boundary in this week's issue of the journal Science.
The results are important for understanding tsunami risk, according to James Allan, program director in NSF's Division of Ocean Sciences.
"Such tidal waves can affect the lives of hundreds of thousands of people and result in billions of dollars in damages, as happened in Southeast Asia in 2004," Allan said. "This research underscores the importance of scientific drillship-based studies, and of collecting oceanographic and geologic data over long periods of time."
The plate boundary earthquake zone off Japan's coast forms part of the "ring of fire" that surrounds the Pacific Ocean. Once the end of a plate sliding -- or subducting -- beneath another reaches a certain depth, the material from the descending plate melts, forming volcanoes that often are located on land. Mount St. Helens in the U.S. is one of these volcanoes, as is Mount Fuji in Japan.
In 2009 and 2010, scientists with the IODP (Integrated Ocean Drilling Program, now the International Ocean Discovery Program) NanTroSEIZE (Nankai Trough Seismogenic Zone Experiment) project drilled two boreholes in the Nankai Trough southwest of Honshu, Japan. The holes were drilled from aboard a scientific drillship. In 2010, also from a scientific drillship, researchers installed monitoring instruments in the holes as part of a network that includes sensors on the seafloor. NSF supports the IODP.
The two boreholes are 6.6 miles apart, straddling the boundary of the last major earthquake in this area, which occurred in 1944 and measured magnitude 8.1. The resulting tsunami, which hit Tokyo, was 26 feet high.
Research shows that slow earthquakes are an important part of fault slip and earthquake occurrence at tectonic plate boundaries. They may explain where some of the energy built up in a fault or a subduction zone goes.
"Until we had these data, no one knew if zero percent or one hundred percent of the energy in the shallow subduction zone was dissipated by slow earthquakes," Saffer said. The scientists found that about 50 percent of the energy is released in slow earthquakes.
The remaining 50 percent, Saffer said, could be taken up in a permanent shortening of one of the plates or be stored for the next 100- or 150-year earthquake.
"We still don't know which is the case, but it makes a big difference for tsunami hazards," Saffer said. "The slow slip could reduce tsunami risk by periodically relieving stress, but it is probably more complicated than just acting as a shock absorber."
The researchers discovered a series of slow slip events where the tectonic plates meet, seaward of an area of recurring magnitude 8 earthquakes. Some of these were triggered by unconnected earthquakes, and some happened spontaneously.
This group of slow earthquakes recurred every 12 to 18 months. "We discovered slow earthquakes of magnitude 5 or 6 in the region that last from days to weeks," Saffer said.
These earthquakes usually go unnoticed because they are so slow and far offshore.
The researchers also note that because earthquakes that occur at a distance from this subduction zone can trigger slow earthquakes, the area is much more sensitive than previously thought.
"The question now is whether it releases stress when these slow earthquakes occur," Saffer said. "Some caution is required in simply concluding that the slow events reduce hazard, because our results also show that the outer part of the subduction area can store strain. Furthermore, are the slow earthquakes doing anything to load deeper parts of the area that do cause big earthquakes? We don't know."
Also part of this project were Achim J. Kopf, MARUM-Center for Marine Environmental Sciences; Laura M. Wallace, GNS Sciences, New Zealand and University of Texas Institute of Geophysics; Toshinori Kimura and Yuya Machida, Japan Agency for Marine-Earth Science and Technology, Kanagawa, Japan; Satoshi Ide, Department of Earth and Planetary Science, University of Tokyo; Earl Davis, Pacific Geoscience Centre, Geological Survey of Canada; and IODP Expedition 365 shipboard scientists.
Cheryl Dybas | EurekAlert!
Stagnation in the South Pacific Explains Natural CO2 Fluctuations
23.02.2018 | Carl von Ossietzky-Universität Oldenburg
First evidence of surprising ocean warming around Galápagos corals
22.02.2018 | University of Arizona
A newly developed laser technology has enabled physicists in the Laboratory for Attosecond Physics (jointly run by LMU Munich and the Max Planck Institute of Quantum Optics) to generate attosecond bursts of high-energy photons of unprecedented intensity. This has made it possible to observe the interaction of multiple photons in a single such pulse with electrons in the inner orbital shell of an atom.
In order to observe the ultrafast electron motion in the inner shells of atoms with short light pulses, the pulses must not only be ultrashort, but very...
A group of researchers led by Andrea Cavalleri at the Max Planck Institute for Structure and Dynamics of Matter (MPSD) in Hamburg has demonstrated a new method enabling precise measurements of the interatomic forces that hold crystalline solids together. The paper Probing the Interatomic Potential of Solids by Strong-Field Nonlinear Phononics, published online in Nature, explains how a terahertz-frequency laser pulse can drive very large deformations of the crystal.
By measuring the highly unusual atomic trajectories under extreme electromagnetic transients, the MPSD group could reconstruct how rigid the atomic bonds are...
Quantum computers may one day solve algorithmic problems which even the biggest supercomputers today can’t manage. But how do you test a quantum computer to...
For the first time, a team of researchers at the Max-Planck Institute (MPI) for Polymer Research in Mainz, Germany, has succeeded in making an integrated circuit (IC) from just a monolayer of a semiconducting polymer via a bottom-up, self-assembly approach.
In the self-assembly process, the semiconducting polymer arranges itself into an ordered monolayer in a transistor. The transistors are binary switches used...
Breakthrough provides a new concept of the design of molecular motors, sensors and electricity generators at nanoscale
Researchers from the Institute of Organic Chemistry and Biochemistry of the CAS (IOCB Prague), Institute of Physics of the CAS (IP CAS) and Palacký University...
15.02.2018 | Event News
13.02.2018 | Event News
12.02.2018 | Event News
23.02.2018 | Physics and Astronomy
23.02.2018 | Health and Medicine
23.02.2018 | Physics and Astronomy