Forum for Science, Industry and Business

Sponsored by:     3M 
Search our Site:

 

New study casts doubt on validity of standard earthquake-prediction model

19.09.2002


A new study by Stanford University geophysicists is raising serious questions about a fundamental technique used to make long-range earthquake predictions.



Writing in the journal Nature, geophysicists Jessica Murray and Paul Segall show how a widely used earthquake model failed to predict when a long-anticipated magnitude 6 quake would strike the San Andreas Fault in Central California.

In their Sept. 19 Nature study, Murray and Segall analyzed the "time-predictable recurrence model" – a technique for estimating the time when an earthquake will occur. This model is used to calculate the probability of future earthquakes.


Developed by Japanese geophysicists K. Shimazaki and T. Nakata in 1980, the time-predictable model has become a standard tool for hazard prediction in many earthquake-prone regions – including the United States, Japan and New Zealand.

Strain build-up

The time-predictable model is based on the theory that earthquakes in fault zones are caused by the constant build-up and release of strain in the Earth’s crust.

"With a plate boundary like the San Andreas, you have the North American plate on one side and the Pacific plate on the other," explained Segall, a professor of geophysics. "The two plates are moving at a very steady rate with respect to one another, so strain is being put into the system at an essentially constant rate."

When an earthquake occurs on the fault, a certain amount of accumulated strain is released, added Murray, a geophysics graduate student.

"Following the quake, strain builds up again because of the continuous grinding of the tectonic plates," she noted. "According to the time-predictable model, if you know the size of the most recent earthquake and the rate of strain accumulation afterwards, you should be able to forecast the time that the next event will happen simply by dividing the strain released by the strain-accumulation rate."

Parkfield, Calif.

Although the model makes sense on paper, Murray and Segall wanted to put it to the test using long-term data collected in an ideal setting. Their choice was Parkfield – a tiny town in Central California midway between San Francisco and Los Angeles. Perched along the San Andreas Fault, Parkfield has been rocked by a magnitude 6 earthquake every 22 years on average since 1857. The last one struck in 1966, and geologists have been collecting earthquake data there ever since.

"Parkfield is a good place to test the model because we have measurements of surface ground motion during the 1966 earthquake and of the strain that’s been accumulating since," Murray noted. "It’s also located in a fairly simple part of the San Andreas system because it’s on the main strand of the fault and doesn’t have other parallel faults running nearby."

When Murray and Segall applied the time-predictable model to the Parkfield data, they came up with a forecast of when the next earthquake would occur.

"According to the model, a magnitude 6 earthquake should have taken place between 1973 and 1987 – but it didn’t," Murray said. "In fact, 15 years have gone by. Our results show, with 95 percent confidence, that it should definitely have happened before now, and it hasn’t, so that shows that the model doesn’t work – at least in this location."

Could the time-predictable method work in other parts of the fault, including the densely populated metropolitan areas of Northern and Southern California? The researchers have their doubts,

"We used the model at Parkfield where things are fairly simple," Murray observed, "but when you come to the Bay Area or Los Angeles, there are a lot more fault interactions, so it’s probably even less likely to work in those places."

Segall agreed: "I have to say, in my heart, I believe this model is too simplistic. It’s really not likely to work elsewhere, either, but we still should test it at other sites. Lots of people do these kinds of calculations. What Jessica has done, however, is to be extremely careful. She really bent over backwards to try to understand what the uncertainties of these kinds of calculations are – consulting with our colleagues in the Stanford Statistics Department just to make sure that this was done as carefully and precisely as anybody knows how to do. So we feel quite confident that there’s no way to fudge out of this by saying there are uncertainties in the data or in the method."

Use with caution

Segall pointed out that government agencies in a number of Pacific Rim countries routinely use this technique for long-range hazard assessments.

For example, the U.S. Geological Survey (USGS) relied on the time-predictable model and two other models in its widely publicized 1999 report projecting a 70-percent probability of a large quake striking the San Francisco Bay Area by 2030.

"We’re in a tough situation, because agencies like the USGS – which have the responsibility for issuing forecasts so that city planners and builders can use the best available knowledge – have to do the best they can with what information they have." Segall observed. "The message I would send to my geophysical colleagues about this model is, ’Use with caution.’"

Technological advances in earthquake science could make long-range forecasting a reality one day, added Murray, pointing to the recently launched San Andreas Fault drilling experiment in Parkfield under the aegis of USGS and Stanford.

In the mean time, people living in earthquake-prone regions should plan for the inevitable.

"I always tell people to prepare," Segall concluded. "We know big earthquakes have happened in the past, we know they will happen again. We just don’t know when."

Mark Shwartz | EurekAlert!
Further information:
http://kilauea.Stanford.EDU/paul/
http://quake.wr.usgs.gov/research/parkfield/index.html
http://geopubs.wr.usgs.gov/open-file/of99-517/

More articles from Earth Sciences:

nachricht Fossil coral reefs show sea level rose in bursts during last warming
19.10.2017 | Rice University

nachricht NASA finds newly formed tropical storm lan over open waters
17.10.2017 | NASA/Goddard Space Flight Center

All articles from Earth Sciences >>>

The most recent press releases about innovation >>>

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

Im Focus: Neutron star merger directly observed for the first time

University of Maryland researchers contribute to historic detection of gravitational waves and light created by event

On August 17, 2017, at 12:41:04 UTC, scientists made the first direct observation of a merger between two neutron stars--the dense, collapsed cores that remain...

Im Focus: Breaking: the first light from two neutron stars merging

Seven new papers describe the first-ever detection of light from a gravitational wave source. The event, caused by two neutron stars colliding and merging together, was dubbed GW170817 because it sent ripples through space-time that reached Earth on 2017 August 17. Around the world, hundreds of excited astronomers mobilized quickly and were able to observe the event using numerous telescopes, providing a wealth of new data.

Previous detections of gravitational waves have all involved the merger of two black holes, a feat that won the 2017 Nobel Prize in Physics earlier this month....

Im Focus: Smart sensors for efficient processes

Material defects in end products can quickly result in failures in many areas of industry, and have a massive impact on the safe use of their products. This is why, in the field of quality assurance, intelligent, nondestructive sensor systems play a key role. They allow testing components and parts in a rapid and cost-efficient manner without destroying the actual product or changing its surface. Experts from the Fraunhofer IZFP in Saarbrücken will be presenting two exhibits at the Blechexpo in Stuttgart from 7–10 November 2017 that allow fast, reliable, and automated characterization of materials and detection of defects (Hall 5, Booth 5306).

When quality testing uses time-consuming destructive test methods, it can result in enormous costs due to damaging or destroying the products. And given that...

Im Focus: Cold molecules on collision course

Using a new cooling technique MPQ scientists succeed at observing collisions in a dense beam of cold and slow dipolar molecules.

How do chemical reactions proceed at extremely low temperatures? The answer requires the investigation of molecular samples that are cold, dense, and slow at...

Im Focus: Shrinking the proton again!

Scientists from the Max Planck Institute of Quantum Optics, using high precision laser spectroscopy of atomic hydrogen, confirm the surprisingly small value of the proton radius determined from muonic hydrogen.

It was one of the breakthroughs of the year 2010: Laser spectroscopy of muonic hydrogen resulted in a value for the proton charge radius that was significantly...

All Focus news of the innovation-report >>>

Anzeige

Anzeige

Event News

ASEAN Member States discuss the future role of renewable energy

17.10.2017 | Event News

World Health Summit 2017: International experts set the course for the future of Global Health

10.10.2017 | Event News

Climate Engineering Conference 2017 Opens in Berlin

10.10.2017 | Event News

 
Latest News

Electrode materials from the microwave oven

19.10.2017 | Materials Sciences

New material for digital memories of the future

19.10.2017 | Materials Sciences

Physics boosts artificial intelligence methods

19.10.2017 | Physics and Astronomy

VideoLinks
B2B-VideoLinks
More VideoLinks >>>