A prolonged attempt to help scientists predict when earthquakes will happen has ended in a sad failure, according to a study published on Thursday in Nature, the British science weekly.
The paper - whose publication coincides with the aftermath of the quake that struck Pakistan and India, killing tens of thousands of people - is based on a long-term project in California.
Scientists sowed a 40-kilometer (25-mile) part of the notorious San Andreas fault, located at the city of Parkfield, with scores of seismic sensors to monitor earth rumbles and movement in real time.
But an earthquake measuring 6.0 on the Richter scale struck that region on September 28, 2004 without any warning. There was not the slightest hint of a build-up of strain or impending landslip.
Parkfield had long been fingered as a good testbed for earthquake physics as it had experienced seven big quakes since 1857, and these events were quite evenly spaced apart.
Because of that, the US Geological Survey (USGS) felt confident enough in 1985 to predict that a 6.0 quake would occur in Parkfield before 1993.
As it happened, the USGS was spot-on when it came to predicting the size of the event and the location, and the data sent back by the sensors was invaluable - but its timing was 11 years out.
In addition, the absence of any precursor signal meant the local population could not be warned in time. "Earthquake prediction is the Holy Grail of seismology," says the report, adding, however: "The 2004 Parkfield earthquake, with its obvious lack of precursors, demonstrates that reliable short-term earthquake prediction is still not achievable."
Given the huge task of achieving predictability, the study recommends that resources be devoted more to improving computer models to help calculate how big a future quake will be and what kind of ground motion it is likely to cause. This would have immediate benefit for people living in the vulnerable area and for rescue services.
One of the most spectacular cases of earthquake prediction was made earlier this year by University of Ulster seismology professor John McCloskey.
In an analysis of the enormous December 26 quake off Sumatra that caused the Indian Ocean tsunami, McCloskey said the stress had placed additional strain on a weak part of the same fault, lying farther south. On March 17, McCloskey's team warned that a quake of 8.5 magnitude in this newly-stressed region was imminent. Eleven days later, an event measuring 8.7 occurred.
The new study is lead-authored by William Bakun of the USGS, based at Menlo Park, California.
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