Since the devastating 921 earthquake that claimed 2,297 lives in 1999, scientists in Taiwan and from overseas have pondered several questions related to the tremor. Why did the earthquake hit central Taiwan? How did the fault slip, causing the earthquake? Why did the quake cause such serious damage?
To answer these questions, scientists have already begun a series of experiments sponsored by the National Science Council (NSC) and conducted along the Chelungpu Fault (
Wang Chien-ying (
PHOTO: CHIU YU-TZU
The Thin-skin Model was presented by seismologists in the 1960s, and argues that so-called shallow detachment surfaces buried underground will cause the earth to thrust upwards during an earthquake.
The theory accurately explains the phenomena seen during the 921 quake, such as why the displacement of the east side of the Chelungpu Fault was greater than on its west side.
Drilling
PHOTO: CHEN CHENG-CHANG, TAIPEI TIMES
Most of the evidence so far has been obtained from drilling exploration and a deep-sounding seismic-reflection experiment which helps scientists picture the structure of the Chelungpu Fault.
Wang and his team have worked on obtaining underground samples of the Chelungpu Fault at two drilling sites. A shallow drilling project with two holes, both about 300m deep, has been sponsored by both Taiwan and Japan.
On Nov. 20 last year, scientists drilled the first hole in Fengyuan (
"By observing samples from the fault we obtained from the drilling project, we can understand the mechanism responsible for the 921 earthquake," Wang said at a press conference held last Thursday at Chienchiou Elementary School (
Japanese scientists and US students have joined Wang's team since November last year to study geophysical characters of the fault.
"We are interested in what is the world's biggest displacement created by the 921 Earthquake in Fengyuan (
Tanaka said that several Japanese scientists have worked with Taiwanese scientists in order to learn more about the earthquake by comparing Taiwan's 921 earthquake with Japan's Kobe earthquake in 1995.
"Some of us [Japanese scientists] have found that activities occurring in the southern part of the Chelungpu Fault are similar to those we observed during the Kobe earthquake," Tanaka said.
Two US graduate students from the Department of Geology at Utah State University, Matt Pachell and Richard Heermance, have worked with Taiwanese geologists in Nantou for months to produce their master's degree theses.
A bigger project
More than nine months after the natural disaster, the NSC initiated PEAR as an inter-governmental project last June. The program has been given a NT$123.5 million budget from the NSC for 49 research proposals. The proposals have been carried out by scientists from a diverse range of governmental agencies, including the NSC, the Central Weather Bureau, the Central Geological Survey and the Water Resource Bureau.
But scientists are still struggling for financial support from the government.
Wang said that scientists from Taiwan, Japan and the US are already planning a proposal to the International Continental Scientific Drilling Program under the UN to request that a deeper hole be dug in Taiwan.
The source of the 921 earthquake has been identified as being eight kilometers under Mingchien township in Nantou. Scientists believe that important information lies in that seismogenic zone (
"If we can drill a five-kilometer hole, we might be able to reveal more secrets buried there and learn more about factors that triggered the 921 earthquake. All countries will benefit from such knowledge," Wang said.
Wang said that such information would be provided as reference for disaster prevention and earthquake prediction for countries sitting on seismic belts.
The international cooperation project, however, still needs to understand Taiwan's basic geological structure. They are currently learning more about this with "deep-sounding seismic-reflection experiments" which are being carried out along the fault line.
To collect this information, six heavy trucks are used to pound the earth's surface near the fault line and 450 receivers located from Taichung to Changhua record waves that bounce back. This experiment is helping scientists draw a detailed geological map of the structure of the fault which can go as deep as 18km underground. A complete map of the Chelungpu Fault will be finished at the end of February.
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