Forum for Science, Industry and Business

Sponsored by:     3M 
Search our Site:

 

Sumatra megaquake defied theory

29.03.2006


The risks of Sumatra-style mega-quakes around the world have been sorely misjudged, say earth scientists who are re-examining some of the pre-December 2004 assumptions scientists made about such rare events.

For more than two decades geologists had thought that the largest quakes, of magnitude 9 and greater, happen when a young tectonic plate is subducted, or shoved quickly, under another plate. But the Great Sumatra-Andaman earthquake of 26 December 2004 didn’t match that pattern at all. The Indian Plate is middle-aged and moving at a middling rate, which throws into question the estimated quake dangers at other similar quake-prone zones near Japan, in the Pacific Northwest, Chile, Alaska, and elsewhere.

"We didn’t expect such a big earthquake in that location," said Emile Okal of Northwestern University. Okal is slated to speak about how the Sumatra-Andaman quake calls into question theoretical assumptions made about other similar dangers zones worldwide and especially in South America on Thursday, 6 April, at Backbone of the Americas - Patagonia to Alaska. The meeting is co-convened by the Geological Society of America and Asociación Geológica Argentina, with collaboration of the Sociedad Geológica de Chile. The meeting takes place 3-7 April in Mendoza, Argentina.



Previous to the catastrophic 26 December 2004 earthquake, the theory about how subduction zones generate quakes was straightforward, says Okal. It boiled down to age and speed. Where an older, colder and therefore denser slab of crust is being pushed slowly under another plate, "It will want to sink," he said. As a result there’s not a lot of stress building up to cause large quakes.

At the other end of that same spectrum are subduction zones where young, buoyant crust is being forced quickly under another plate. The rate of "convergence" and the fact that the young crust resists sinking causes lots of stress to build up and results in much larger quakes.

"So you could take a map of all the subduction zones of the world and look at it," said Okal. "The red areas were ones with younger, faster moving crust and the blue areas were older, slow moving crust."

The theory seemed tidy enough and could be verified somewhat by dating the crust, measuring the rates entire tectonic plates seemed to be moving at, and estimating the power of past quakes from historical accounts. According to the theory, the Sumatra subduction zone was capable of no more than a magnitude 8 earthquake, Okal explains.

"The cold shower we got was Sumatra," said Okal. "We have a 9.3 on our hands. You got a point that violates the plan outrageously."

Fortunately, says Okal, the science of plate tectonics has made great strides since the 1980s and the danger map now can be greatly refined and reassessed. For instance, where once researchers looked to the centers of plates to see how fast they may be colliding at the edges, Global Positioning System technology now allows geophysicists to track specific movements and deformation in the actual subduction zone.

The result is that some places may be at greater risk of large quakes, and others may be at lesser risk. "Suddenly there are points moving up and down when you reassess them," he said.

It’s been discovered, for instance, that despite being one of the best big-quake factories on the planet, the convergence of the Nazca Plate and the South American Plate on the Pacific Coast of South America is happening at a significantly slower rate than previously thought, says Okal.

On the other hand, some subduction zones have quakes that do not directly express the subduction - and so have inflated the apparent risk of a large event. One example is in the Caribbean where, besides a subduction zone, there are quakes that occur along strike-slip, San Andreas-type, faults. These faults accommodate sideways movement in the collision zone instead of the blunt shoving of one plate under another. "So we are reassessing this whole area," said Okal. There is also the matter of how subduction zones let loose their built-up energy. They can break along small segments, together or individually. One segment might produce a moderate quake. But if four or five segments all go at once you get a colossal release of seismic energy, like that seen when the Sumatra-Andaman zone "unzipped" for 800 miles (nearly 1,300 kilometers) on that terrible day 15 months ago.

"The bottom line is that we have to be very humble," said Okal. We don’t know how to predict the size of quakes, he said, and we should not discount that there will be surprises.

WHEN & WHERE
Backbone of the Americas - Patagonia to Alaska
Centro de Congressos
Mendoza, Argentina
Thursday, 6 April 2006

Ann Cairns | EurekAlert!
Further information:
http://www.geosociety.org
http://www.earth.northwestern.edu

More articles from Earth Sciences:

nachricht Fast rising bedrock below West Antarctica reveals an extremely fluid Earth mantle
22.06.2018 | Technical University of Denmark

nachricht Polar ice may be softer than we thought
22.06.2018 | Eberhard Karls Universität Tübingen

All articles from Earth Sciences >>>

The most recent press releases about innovation >>>

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

Im Focus: Temperature-controlled fiber-optic light source with liquid core

In a recent publication in the renowned journal Optica, scientists of Leibniz-Institute of Photonic Technology (Leibniz IPHT) in Jena showed that they can accurately control the optical properties of liquid-core fiber lasers and therefore their spectral band width by temperature and pressure tuning.

Already last year, the researchers provided experimental proof of a new dynamic of hybrid solitons– temporally and spectrally stationary light waves resulting...

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...

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

Graphene assembled film shows higher thermal conductivity than graphite film

22.06.2018 | Materials Sciences

Fast rising bedrock below West Antarctica reveals an extremely fluid Earth mantle

22.06.2018 | Earth Sciences

Zebrafish's near 360 degree UV-vision knocks stripes off Google Street View

22.06.2018 | Life Sciences

VideoLinks
Science & Research
Overview of more VideoLinks >>>