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Stories of the Brave and the Perseverant

Breakthrough in precursor studies key to earthquake prediction

 
921 大地震讓台灣的人民更警覺,學術與研究單位也加強相關的預警研究。
 

by Deborah Kuo CNA staff writer
 

People are scared of earthquakes mostly because of their unpredictability.

For decades, seismologists have dreamed of being able to divine the time and place of the next disastrous shock. But the behavior of quake-prone faults has proved so complex that the experts have been forced to conclude that large tremors are isolated, random and unpredictable.

Industrially advanced countries have made commendable progress over the past several decades in earth sciences, but the prediction of the time, epicenter and magnitude of major earthquakes is a problem that has not been solved.

"We're still finding the ways to predict earthquakes, like a blind man feeling an elephant, " said Shin Tsai-chin, deputy director of the Central Weather Bureau (CWB) , who oversees the bureau's Seismic Network.


Nantou County Fire Department helps people out of a building during a drill in ChiChi.(Sep 21, 2000 CNA)


The report of National Center for Research on Earthquake Engineering shows that aftershocks caused by the 921 Earthquake are moving east. (Sep 24, 1999 CNA)

Taiwan is located in a strongly oblique convergent zone between the Eurasian Plate and the Philippine Sea Plate, an area commonly referred to as the Pacific Ring of Fire. According to the CWB Seismic Network, the Taiwan area has about 16,000 to 18,000 detectable earthquakes each year, about 250 of which are of magnitude 4.0 and about 30 of which are magnitude 5.0 or larger.

Yilan in the northeast and Hualien in the east are the most earthquake-prone counties in Taiwan. However, a deadly 7.3 magnitude earthquake unexpectedly struck Taiwan Sept. 21, 1999, with its epicenter located near the town of Chi-Chi in central Taiwan -- not close to the more active seismic zones of Yilan and Hualien.

The earthquake -- the most serious disaster since World War II in Taiwan -- left some 2,500 people dead and 100,000 houses destroyed, and seriously disrupted the local economy as it occurred near the island's densely populated western plain.

Shin said seismologists may have gained some knowledge from labs and theoretical studies about earthquake precursors, but when it comes to reality, they have a hard time telling whether the phenomena they have detected can be coded as earthquake precursors.

Taking the CWB's experience as an example, he said, prominent short-term anomalies or dynamic tendencies of underground water levels are often detected in its seismological observation station in Hualien prior to certain major earthquakes, but there have been incidents in which underground water levels have had no changes at all before some quakes of similar magnitude have struck.

Shin said one of the things that make earthquake predictions impossible is that the prediction theory or method that proves to be effective at one location does not necessarily prove to be applicable to other localities, because all locations vary in terms of geological structure.

For example, he said, some historical accounts show that there have been apparent foreshocks before some major earthquakes have occurred, but many devastating quakes have struck without any foreshocks.

Japan, the United States and China have spent money and manpower in earthquake prediction research over the past 30-odd years, while Russia, Italy, Greece and Taiwan have started to catch up.

There have been cases that have proved to be successful in earthquake predictions in China, such as one made in 1975 that pre-warned an incoming disastrous jolt for Haicheng City in Liaoning Province, helping reduce damage to lives and property.

Nevertheless, the same theory and technology applied in an area of northeastern China failed to divine in advance a killer earthquake that battered Tangshan the following year that left more than 250,000 people dead.

Earth scientists have worked from various angles -- crustal deformation, plate behavior and alteration of underground water levels -- to try to divine when, where and how disastrous earthquakes occur, in the hope that someday, seismologists will be able to forecast major quakes the same way they forecast typhoons, Shin said.

Meanwhile, he went on, the CWB's earthquake prediction research has mainly focused on observation and analysis of mass transfer and rock dilation of the Earth's crust, as well as the short-term anomalies or dynamic tendencies of underground water levels before major earthquakes.

Since the devastating 921 Chi-Chi earthquake, the CWB has installed global positioning systems (GPS) at 150 earthquake observation spots nationwide, aimed at detecting crustal activities before and after major quakes.

The weather bureau has also dug a deep well in Hualien, hoping that variations in the underground water levels in the 300-meter well will tell when and how earthquakes occur.

So far, however, they have failed to obtain effective evidence provided by the well to prove that variations in underground water levels have direct or definite relationships to earthquakes, Shin noted.

Meanwhile, he continued, the CWB has received many phone calls from enthusiastic members of the public who claim to have an instinct for forecasting earthquakes. In one case, he said, a man said he develops tinnitus prior to a major earthquake. After quantitative verification, however, most of the predictions have proved wrong.

Aware that improper forecasting of a major earthquake based only on superstition could trigger social anxiety or even instability, the CWB never makes any temblor forecasts based on the "precognition" of an individual, Shin stressed.

Many people have also shown great interest in animal precursors, Shin went on, but pointed out that animal behavior can be altered by too many factors and so far, no government in the world has made serious research on the relationship between animal behavior and earthquakes.

Besides the CWB, other research institutes have also been doing research on earthquake precursors.

According to Shin, the Institute of Earth Sciences under Academia Sinica has established eight earthquake monitoring stations around the country since 1988 aimed at discerning the relationship between major earthquakes and geomagnetic fluctuations.

So far, they have not been able to determine the reasons behind geomagnetic fluctuations and their physical mechanism, Shin said.

Several leading local universities, including National Taiwan Central University and National Taiwan University, have also set up task forces to research the possibility of short-term earthquake prediction on the basis of electromagnetic field variations under, on, or over the Earth's surface and near space.

"Despite being an uphill battle, earthquake prediction research must go on," Shin concluded.

 
 
 
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