Forum for Science, Industry and Business

Sponsored by:     3M 
Search our Site:

 

’Clusters’ of earthquakes yield an ominous scenario

03.01.2005


The newest studies on the Cascadia Subduction Zone off the coast of the Pacific Northwest have identified a "clustering" of great earthquakes of the type that would cause a major tsunami, yielding a historical record with two distinct implications - one that’s good, the other not.

According to scientists at Oregon State University, this subduction zone has just experienced a cluster of four massive earthquakes during the past 1600 years, and if historical trends continue, this cluster could be over and the zone may already have entered a long quiet period of 500 to 1,000 years, which appears to be common following a cluster of earthquake events.

Alternatively, the current cluster of earthquakes may have one or more events left in it – some clusters within the past 10,000 years have had clusters of up to five events – and within a cluster, the average time interval between earthquakes is 300 years. Since the last major Cascadia earthquake occurred in the year 1700, the next event may well be imminent.



"The Cascadia Subduction Zone has the longest recorded data about its earthquakes of any major fault in the world," said Chris Goldfinger, an associate professor of marine geology at OSU and one of the leading experts on this fault zone. "So we know quite a bit about the periodicity of this fault zone and what to expect. But the key point we don’t know is whether the current cluster of earthquake activity is over yet, or does it have another event left in it."

The two most recent major earthquakes on this fault occurred in the year 1700 and approximately the year 1500, Goldfinger said. Those two events were only 200 years apart, and it’s now been 305 years since the last one. From this perspective, there’s some reason to believe the next major earthquake could happen soon.

As the death toll and catastrophic destruction from the East Asia earthquake of last Monday continues to mount, more and more attention is turning to the local version of that geologic setting – the Cascadia Subduction Zone.

According to Goldfinger, there are only two places in the United States with active subduction zones, or major areas where one of the Earth’s great plates are being subducted, or forced underneath the other. One is in Alaska, the site of the great earthquake of 1964. The other is the Cascadia zone, a 600-mile long fault zone that runs from Cape Mendocino in California to Vancouver Island in southern British Columbia.

Major studies have been done on this fault zone, many of them at OSU, and they have identified 19-21 major earthquake events during the past 10,000 years. During at least 17 of these events, the entire fault zone appears to have ruptured at once, causing an earthquake around magnitude 9, and major tsunamis.

"There’s some variation in intensity, the last event in 1700 appeared to be about average," Goldfinger said. "To track these events we use radiocarbon dating of deposits of sand called turbidites, which come from marine landslides. These deep-sea cores give us a pretty accurate picture of when and where an earthquake event happened."

According to Goldfinger, there are remarkable geologic parallels between what just happened in East Asia and what could happen in the Pacific Northwest. The Asian event happened where the India plate was being subducted beneath the Burma microplate, and it ruptured – for the first time since 1833 - along a 600-mile front that is just about the same length as the Cascadia Subduction Zone.

That earthquake happened as the Indian plate moved towards the northeast beneath Asia, just like the Juan de Fuca plate is in the Pacific Northwest before it disappears beneath the North American plate.

What happened in Asia may give a vivid demonstration of the geologic future of the Pacific Northwest. For hundreds of years, these subduction zone plates remain locked, releasing little of their tension. The plate which is being subducted is forced down, while the plate above bulges upwards. Then, in a few minutes of violence every few centuries, the forces are released. The upper plate moves seaward, and a massive tsunami can be produced along with catastrophic destruction from earthquake shaking.

"In the case of the Cascadia Subduction Zone, you could have an area of ocean sea floor that’s 50 miles wide and 500-600 miles long suddenly snap back up, causing a huge tsunami," Goldfinger said. "At the same time, we could expect some parts of the upper, or North American plate to sink one to two meters. These are massive tectonic events. Subduction zones produce the most powerful earthquakes and tsunamis in the world."

The question, Goldfinger says, is not whether or not the Cascadia Subduction Zone will break again. It’s when. And that’s where the study of past events may shed light on the present.

Following are the earthquake events on this fault zone during the past 9,800 years:

  • Oldest recorded earthquake, 9,800 years before present
  • 800 year gap with no major earthquakes
  • Three earthquake events, 8,300 to 9,000 years before present
  • 700 year gap with no major earthquakes
  • Five earthquake events, 5,700 to 7,600 years before present
  • 1000 year gap with no major earthquakes
  • Two earthquake events, 3,900 to 4,700 years before present
  • 500 year gap with no major earthquakes
  • Three earthquake events, 2,500 to 3,400 years before present
  • 700 to 900 year gap with no major earthquakes
  • Four earthquake events from 1600 years before present to today

"We’re going to continue to study the geology of these events and identify the patterns and likelihood of future events as best we can," Goldfinger said. "A few things are clear. There are clusters of earthquake events on the Cascadia Subduction Zone, and there are big gaps. And we’re either in a cluster right now or at the end of one."

"Whether the current cluster is over yet, we just don’t know," he said. "One possibility is that we could be done with this cluster and looking at a period of many hundreds of years before the next earthquake."

"The other distinct possibility is we could still be in a cluster of events. If that’s the case, the average time interval between earthquakes within a cluster is already up. We would be due just about any day."

Chris Goldfinger | EurekAlert!
Further information:
http://www.oregonstate.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: Fizzy soda water could be key to clean manufacture of flat wonder material: Graphene

Whether you call it effervescent, fizzy, or sparkling, carbonated water is making a comeback as a beverage. Aside from quenching thirst, researchers at the University of Illinois at Urbana-Champaign have discovered a new use for these "bubbly" concoctions that will have major impact on the manufacturer of the world's thinnest, flattest, and one most useful materials -- graphene.

As graphene's popularity grows as an advanced "wonder" material, the speed and quality at which it can be manufactured will be paramount. With that in mind,...

Im Focus: Exotic quantum states made from light: Physicists create optical “wells” for a super-photon

Physicists at the University of Bonn have managed to create optical hollows and more complex patterns into which the light of a Bose-Einstein condensate flows. The creation of such highly low-loss structures for light is a prerequisite for complex light circuits, such as for quantum information processing for a new generation of computers. The researchers are now presenting their results in the journal Nature Photonics.

Light particles (photons) occur as tiny, indivisible portions. Many thousands of these light portions can be merged to form a single super-photon if they are...

Im Focus: Circular RNA linked to brain function

For the first time, scientists have shown that circular RNA is linked to brain function. When a RNA molecule called Cdr1as was deleted from the genome of mice, the animals had problems filtering out unnecessary information – like patients suffering from neuropsychiatric disorders.

While hundreds of circular RNAs (circRNAs) are abundant in mammalian brains, one big question has remained unanswered: What are they actually good for? In the...

Im Focus: RAVAN CubeSat measures Earth's outgoing energy

An experimental small satellite has successfully collected and delivered data on a key measurement for predicting changes in Earth's climate.

The Radiometer Assessment using Vertically Aligned Nanotubes (RAVAN) CubeSat was launched into low-Earth orbit on Nov. 11, 2016, in order to test new...

Im Focus: Scientists shine new light on the “other high temperature superconductor”

A study led by scientists of the Max Planck Institute for the Structure and Dynamics of Matter (MPSD) at the Center for Free-Electron Laser Science in Hamburg presents evidence of the coexistence of superconductivity and “charge-density-waves” in compounds of the poorly-studied family of bismuthates. This observation opens up new perspectives for a deeper understanding of the phenomenon of high-temperature superconductivity, a topic which is at the core of condensed matter research since more than 30 years. The paper by Nicoletti et al has been published in the PNAS.

Since the beginning of the 20th century, superconductivity had been observed in some metals at temperatures only a few degrees above the absolute zero (minus...

All Focus news of the innovation-report >>>

Anzeige

Anzeige

Event News

Call for Papers – ICNFT 2018, 5th International Conference on New Forming Technology

16.08.2017 | Event News

Sustainability is the business model of tomorrow

04.08.2017 | Event News

Clash of Realities 2017: Registration now open. International Conference at TH Köln

26.07.2017 | Event News

 
Latest News

A Map of the Cell’s Power Station

18.08.2017 | Life Sciences

Engineering team images tiny quasicrystals as they form

18.08.2017 | Physics and Astronomy

Researchers printed graphene-like materials with inkjet

18.08.2017 | Materials Sciences

VideoLinks
B2B-VideoLinks
More VideoLinks >>>