Forum for Science, Industry and Business

Sponsored by:     3M 
Search our Site:

 

Slow earthquakes in ocean subduction zones shed light on tsunami risk

19.06.2017

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.

Media Contact

Cheryl Dybas
cdybas@nsf.gov

 @NSF

http://www.nsf.gov 

Cheryl Dybas | EurekAlert!

More articles from Earth Sciences:

nachricht Novel method for investigating pore geometry in rocks
18.06.2018 | Kyushu University, I2CNER

nachricht Decades of satellite monitoring reveal Antarctic ice loss
14.06.2018 | University of Maryland

All articles from Earth Sciences >>>

The most recent press releases about innovation >>>

Die letzten 5 Focus-News des innovations-reports im Überblick:

Im Focus: Overdosing on Calcium

Nano crystals impact stem cell fate during bone formation

Scientists from the University of Freiburg and the University of Basel identified a master regulator for bone regeneration. Prasad Shastri, Professor of...

Im Focus: AchemAsia 2019 will take place in Shanghai

Moving into its fourth decade, AchemAsia is setting out for new horizons: The International Expo and Innovation Forum for Sustainable Chemical Production will take place from 21-23 May 2019 in Shanghai, China. With an updated event profile, the eleventh edition focusses on topics that are especially relevant for the Chinese process industry, putting a strong emphasis on sustainability and innovation.

Founded in 1989 as a spin-off of ACHEMA to cater to the needs of China’s then developing industry, AchemAsia has since grown into a platform where the latest...

Im Focus: First real-time test of Li-Fi utilization for the industrial Internet of Things

The BMBF-funded OWICELLS project was successfully completed with a final presentation at the BMW plant in Munich. The presentation demonstrated a Li-Fi communication with a mobile robot, while the robot carried out usual production processes (welding, moving and testing parts) in a 5x5m² production cell. The robust, optical wireless transmission is based on spatial diversity; in other words, data is sent and received simultaneously by several LEDs and several photodiodes. The system can transmit data at more than 100 Mbit/s and five milliseconds latency.

Modern production technologies in the automobile industry must become more flexible in order to fulfil individual customer requirements.

Im Focus: Sharp images with flexible fibers

An international team of scientists has discovered a new way to transfer image information through multimodal fibers with almost no distortion - even if the fiber is bent. The results of the study, to which scientist from the Leibniz-Institute of Photonic Technology Jena (Leibniz IPHT) contributed, were published on 6thJune in the highly-cited journal Physical Review Letters.

Endoscopes allow doctors to see into a patient’s body like through a keyhole. Typically, the images are transmitted via a bundle of several hundreds of optical...

Im Focus: Photoexcited graphene puzzle solved

A boost for graphene-based light detectors

Light detection and control lies at the heart of many modern device applications, such as smartphone cameras. Using graphene as a light-sensitive material for...

All Focus news of the innovation-report >>>

Anzeige

Anzeige

VideoLinks
Industry & Economy
Event News

Munich conference on asteroid detection, tracking and defense

13.06.2018 | Event News

2nd International Baltic Earth Conference in Denmark: “The Baltic Sea region in Transition”

08.06.2018 | Event News

ISEKI_Food 2018: Conference with Holistic View of Food Production

05.06.2018 | Event News

 
Latest News

Carbon nanotube optics provide optical-based quantum cryptography and quantum computing

19.06.2018 | Physics and Astronomy

How to track and trace a protein: Nanosensors monitor intracellular deliveries

19.06.2018 | Life Sciences

New material for splitting water

19.06.2018 | Physics and Astronomy

VideoLinks
Science & Research
Overview of more VideoLinks >>>