Forum for Science, Industry and Business

Sponsored by:     3M 
Search our Site:

 

Sediment could be a major factor in biggest subduction zone earthquakes

31.01.2006


The most powerful earthquakes – such as those that shook Indonesia in 2004, Alaska in 1964, Chile in 1960 and the Pacific Northwest in 1700 – occur in subduction zones, areas of the sea floor just offshore where two tectonic plates meet and one dives beneath the other.



But not all subduction zones are created equal, and University of Washington researchers believe they have found a key to determine which subduction zones – or which specific areas within a subduction zone – might produce the most severe shaking when they rupture.

As the subducting plate slides beneath the upper plate, stress begins to build where the plates meet and the upper plate can deform to create a large structure called a forearc basin. The basin, a sort of a bowl-shaped depression, fills with sediment from nearby rivers that empty into the ocean. Over millions of years, the sediment typically piles to great depths, from a half-mile to nearly 2 miles, and in rare cases might reach 3 miles deep, said Christopher Fuller, a University of Washington doctoral student in Earth and space sciences.


"In many of them, the sediment will stop the deformation of the upper plate," Fuller said. "The simplest way to think of it is that the increased weight of the sediment stops the deformation from occurring."

It appears the most severe subduction zone earthquakes occur in areas where such sediment-filled basins are found, but the reasons aren’t exactly clear. Fuller and his colleagues conducted computer simulations of force experienced during plate subduction to determine how sediment buildup influences major earthquakes. They found that the weight of the sediment strengthens the edge of the plate directly above where the earthquakes happen. The stronger edge is deformed far less by subduction than nearby areas without such basins, he said, and that increases the likelihood that large earthquakes will occur in regions with basins.

Fuller is the lead author of a paper explaining the modeling research, published in the February edition of the journal Geology. Co-authors are Sean Willett, a UW associate professor of Earth and space sciences, and Mark Brandon, a professor of geology and geophysics at Yale University. The work was supported by grants from the National Science Foundation.

Hypotheses for why earthquakes associated with forearc basins can be so severe include:

  • Changing conditions where the plates meet, as the top part of the subducting plate meets more resistance and travels at a slower speed than the bottom part of the plate, creating a great strain in the plate. Fuller regards this as the least likely scenario.

  • Fault strengthening over time, like the seal a mayonnaise jar lid develops when it hasn’t been opened for weeks. Slight movement on the fault caused by deformation within the upper plate (like tapping the jar lid) loosens the bonds and then the fault suddenly moves (like twisting the jar lid). Fuller believes this is the most likely hypothesis.

  • Fluid between the plates becomes superheated under pressure and, like water boiling in a teakettle, the fluid pushes upward and counteracts the downward pressure from the upper plate, allowing the fault to rupture.

The Cascadia subduction zone off the coasts of Washington, Oregon and northern California has forearc basins in several areas, Fuller said. As it moves to the east at 2 inches a year, the Juan de Fuca tectonic plate slides beneath the North American plate that contains the landmass of the Pacific Northwest. In the process, sediment as deep as 1½ miles is scraped off the top of the Juan de Fuca plate and is deformed into surface depressions on the North American plate, forming the basins where sediment from coastal rivers is deposited. The probability of large earthquakes is greatest in these areas.

The modeling could have implications in figuring out where, within a subduction zone such as Cascadia, great earthquakes are the most likely to occur, Fuller said. But the work is not applicable to every subduction zone because each has different characteristics. For instance, forearc basins do not play the same role in the subduction zone off the Indonesian island of Sumatra, where the massive 2004 earthquake triggered tsunamis that killed hundreds of thousands of people.

"You have to understand the nature of basins and how they work in each area before you can use them as an interpretive tool," Fuller said. "You can’t just apply these correlations everywhere."

Vince Stricherz | EurekAlert!
Further information:
http://www.washington.edu

All articles from Earth Sciences >>>

The most recent press releases about innovation >>>

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

Im Focus: It’s All in the Mix: Jülich Researchers are Developing Fast-Charging Solid-State Batteries

There are currently great hopes for solid-state batteries. They contain no liquid parts that could leak or catch fire. For this reason, they do not require cooling and are considered to be much safer, more reliable, and longer lasting than traditional lithium-ion batteries. Jülich scientists have now introduced a new concept that allows currents up to ten times greater during charging and discharging than previously described in the literature. The improvement was achieved by a “clever” choice of materials with a focus on consistently good compatibility. All components were made from phosphate compounds, which are well matched both chemically and mechanically.

The low current is considered one of the biggest hurdles in the development of solid-state batteries. It is the reason why the batteries take a relatively long...

Im Focus: Color effects from transparent 3D-printed nanostructures

New design tool automatically creates nanostructure 3D-print templates for user-given colors
Scientists present work at prestigious SIGGRAPH conference

Most of the objects we see are colored by pigments, but using pigments has disadvantages: such colors can fade, industrial pigments are often toxic, and...

Im Focus: Unraveling the nature of 'whistlers' from space in the lab

A new study sheds light on how ultralow frequency radio waves and plasmas interact

Scientists at the University of California, Los Angeles present new research on a curious cosmic phenomenon known as "whistlers" -- very low frequency packets...

Im Focus: New interactive machine learning tool makes car designs more aerodynamic

Scientists develop first tool to use machine learning methods to compute flow around interactively designable 3D objects. Tool will be presented at this year’s prestigious SIGGRAPH conference.

When engineers or designers want to test the aerodynamic properties of the newly designed shape of a car, airplane, or other object, they would normally model...

Im Focus: Robots as 'pump attendants': TU Graz develops robot-controlled rapid charging system for e-vehicles

Researchers from TU Graz and their industry partners have unveiled a world first: the prototype of a robot-controlled, high-speed combined charging system (CCS) for electric vehicles that enables series charging of cars in various parking positions.

Global demand for electric vehicles is forecast to rise sharply: by 2025, the number of new vehicle registrations is expected to reach 25 million per year....

All Focus news of the innovation-report >>>

Anzeige

Anzeige

VideoLinks
Industry & Economy
Event News

LaserForum 2018 deals with 3D production of components

17.08.2018 | Event News

Within reach of the Universe

08.08.2018 | Event News

A journey through the history of microscopy – new exhibition opens at the MDC

27.07.2018 | Event News

 
Latest News

Biosensor allows real-time oxygen monitoring for 'organs-on-a-chip'

21.08.2018 | Medical Engineering

Researchers discover link between magnetic field strength and temperature

21.08.2018 | Physics and Astronomy

IHP technology ready for space flights

21.08.2018 | Power and Electrical Engineering

VideoLinks
Science & Research
Overview of more VideoLinks >>>