FEATURE: CWB looking for quake precursors

MISSION IMPOSSIBLE?: A prediction theory that is effective for one area may not be applicable to other places because of different geological structures


Tue, Aug 04, 2009 - Page 2

Seismologists have dreamed for decades of being able to predict earthquakes, but the behavior of quake-prone faults has proved so complex that experts have been forced to conclude that large tremors are isolated, random and unpredictable.

Predicting the time, epicenter and magnitude of major quakes is a problem that has not been solved.

“We’re still finding ways to predict earthquakes,” said Central Weather Bureau (CWB) Deputy Director Shin Tsai-chin (辛在勤), who oversees the bureau’s Seismic Network.

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. The Seismic Network says Taiwan has about 16,000 to 18,000 detectable earthquakes each year, about 250 of which measure at least 4 on the Richter scale and about 30 of which are magnitude 5 or larger.

Ilan and Hualien are the most earthquake-prone counties in the country. However, the epicenter of the massive 921 Earthquake in 1999, which measured 7.3 on the Richter scale, was near the town of Chichi (集集) in Nantou County.

The earthquake killed 2,500 people, destroyed 100,000 houses and seriously disrupted the economy.

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 considered earthquake precursors.

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, he said, but there have been incidents in which underground water levels have not changed at all before other quakes of similar magnitude have struck.

Shin said one of the things that make quake predictions impossible is that the prediction theory or method that is effective at one location may not be applicable to other localities because of geological structures.

Some historical accounts show that there were apparent foreshocks before some major earthquakes, but many devastating quakes have struck without any foreshocks, he said.

Japan, the US and China have spent money and manpower in earthquake prediction research over the past 30 years or so, while Russia, Italy, Greece and Taiwan have started to catch up.

There have been cases of successful earthquake predictions in China, such as one in 1975 that warned of a disastrous jolt in Haicheng City, Liaoning Province, helping reduce loss of life and damage to property.

The same theory and technology failed to predict the 1976 killer earthquake in Tangshan that killed more than 250,000 people.

Scientists have worked from various angles — crustal deformation, plate behavior and alteration of underground water levels — to try to determine 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.

The bureau’s research has 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 quakes, he said.

Since the devastating 921 Earthquake, the bureau has installed global positioning systems at 150 earthquake observation spots nationwide, aimed at detecting crustal activities before and after major quakes.

It has also dug a deep well in Hualien, hoping that variations in the underground water levels in the 300m well will tell when and how earthquakes occur.

So far, 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 said.

The bureau often receives telephone calls from people who claim to have a talent for forecasting earthquakes, Shin said, such as the man who claimed he develops tinnitus before a major quake. Quantitative verification, however, has shown most of the predictions were wrong.

Many people have also shown great interest in animal precursors, Shin said, but no government in the world has yet conducted serious research on the relationship between animal behavior and earthquakes.

The bureau is not the only agency in Taiwan conducting research on earthquake precursors.

Academia Sinica’s Institute of Earth Sciences has established eight earthquake monitoring stations around the country since 1988 aimed at discerning the relationship between major quakes and geomagnetic fluctuations, Shin said.

They have not been able to determine the reasons behind geomagnetic fluctuations and their physical mechanism, he said.

Local universities, including National Taiwan Central University and National Taiwan University, are studying 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, he said.

“Despite being an uphill battle, earthquake prediction research must go on,” Shin said.