# Forum for Science, Industry and Business

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."

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:

Hundreds of bubble streams link biology, seismology off Washington's coast
22.03.2019 | University of Washington

Atmospheric scientists reveal the effect of sea-ice loss on Arctic warming
11.03.2019 | Institute of Atmospheric Physics, Chinese Academy of Sciences

### Im Focus: The taming of the light screw

DESY and MPSD scientists create high-order harmonics from solids with controlled polarization states, taking advantage of both crystal symmetry and attosecond electronic dynamics. The newly demonstrated technique might find intriguing applications in petahertz electronics and for spectroscopic studies of novel quantum materials.

The nonlinear process of high-order harmonic generation (HHG) in gases is one of the cornerstones of attosecond science (an attosecond is a billionth of a...

### Im Focus: Magnetic micro-boats

Nano- and microtechnology are promising candidates not only for medical applications such as drug delivery but also for the creation of little robots or flexible integrated sensors. Scientists from the Max Planck Institute for Polymer Research (MPI-P) have created magnetic microparticles, with a newly developed method, that could pave the way for building micro-motors or guiding drugs in the human body to a target, like a tumor. The preparation of such structures as well as their remote-control can be regulated using magnetic fields and therefore can find application in an array of domains.

The magnetic properties of a material control how this material responds to the presence of a magnetic field. Iron oxide is the main component of rust but also...

### Im Focus: Self-healing coating made of corn starch makes small scratches disappear through heat

Due to the special arrangement of its molecules, a new coating made of corn starch is able to repair small scratches by itself through heat: The cross-linking via ring-shaped molecules makes the material mobile, so that it compensates for the scratches and these disappear again.

Superficial micro-scratches on the car body or on other high-gloss surfaces are harmless, but annoying. Especially in the luxury segment such surfaces are...

### Im Focus: Stellar cartography

The Potsdam Echelle Polarimetric and Spectroscopic Instrument (PEPSI) at the Large Binocular Telescope (LBT) in Arizona released its first image of the surface magnetic field of another star. In a paper in the European journal Astronomy & Astrophysics, the PEPSI team presents a Zeeman- Doppler-Image of the surface of the magnetically active star II Pegasi.

A special technique allows astronomers to resolve the surfaces of faraway stars. Those are otherwise only seen as point sources, even in the largest telescopes...

### Im Focus: Heading towards a tsunami of light

Researchers at Chalmers University of Technology and the University of Gothenburg, Sweden, have proposed a way to create a completely new source of radiation. Ultra-intense light pulses consist of the motion of a single wave and can be described as a tsunami of light. The strong wave can be used to study interactions between matter and light in a unique way. Their research is now published in the scientific journal Physical Review Letters.

"This source of radiation lets us look at reality through a new angle - it is like twisting a mirror and discovering something completely different," says...

All Focus news of the innovation-report >>>

Anzeige

Anzeige