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Unveiling the Mystery of Giant Earthquake Cycles-Internationally Renowned Journal "Science" Published the Top Notch Results of NTU Seismic Research Team

Super strong earthquakes could claim the lives of countless people just overnight. For instance, the South Asia tsunami triggered by a large earthquake in the Northern side of Sumatra Islands on December 26th, 2004, caused the death of 250,000 people. That horrible scene is still fresh in our memories. Last year, on September 12, on the Mentowai Island south to the Sumatra archipelago, a giant earthquake which registered 8.4 on the Richter scale took place. Two centuries ago, in 1833, an earthquake of 9.0 magnitude also occurred, and triggered off a giant tsunami which spread over to Asia, Australia, and Africa. Therefore, for seismologists, the largest issues of their research are:
(1) To increase the accuracy of their inferences about the earthquake cycles;
(2) To reconstruct the long term earthquake cycles;
(3) To predict accurately earthquakes and tsunamis that will take place in the future;
(4) To provide relevant information to these governments of South-Asian countries, so that these government can take proper precautions.

Dr. Chuan-Chou Shen, an Associate Professor of NTU's Department of Geology, collaborated with four research teams (including Professor Kerry Sieh of California Institute of Technology) and published their latest research results in the internationally renowned journal "Science." According to this article, researchers can use the features of coastal corals to record seismic events, and also to enhance significantly the accuracy of the calculation of earthquake cycles. Their methodology has led to a reduction of the margin of error from decades or even hundreds of years to only several years or even less than a year. Consequently, Dr. Shen's research is a major breakthrough in earthquake predictions.

Dr. Shen majored in chemistry for his baccalaureate and graduate degrees, He pointed out that porites cylindrica, a type of coral that grows in the inter-tidal zone around seashores, had a tendency to change its outer appearance in relation to the drastic change of the sea level caused by earthquakes. Over the last decade or so, the California Institute of Technology and the University of Minnesota utilized coral morphology and features of porites cylindrical to achieve an understanding of seismic activities that took place in modern times. But so far the researchers of these two institutes have not been able to grapple with the laws of earthquakes and figure out the context under which giant earthquakes took place once in a long while. The greatest difficulty stemmed from their inability to determine the age of the ancient coral fossils found in the Southeast Asian waters. It wasn't until five years ago when the research team from NTU's Department of Geology joined their efforts that they were able to achieve a new breakthrough.

The NTU research team led by Dr. Shen developed a "Uranium Coral Dating Technique". Utilizing three kinds of radiogenic nuclides in the uranium -238 decay series---- U-238, U-234, and Thorium—230, Dr. Shen and his team members were able to determine the age of the corals through the relative ratio of these three nuclides. Since their degree of precision was very high, and the margin of error was cut down to one year or less, their research results were permitted to appear in the most important international journal of geochemistry—Geochemica et Cosmochimica Acta. Integrating high precision dating techniques and coral morphology analyses, after years of strenuous research, Dr. Shen was finally able to reconstruct the earthquake cycles on Mentowai Island. He and his team members found that during the last seven hundred years the region of the Sumatra Islands experienced a cluster of large earthquakes which continued for several decades every two hundred years, registering about 8 on the Richter scale. After the occurrence of several large earthquakes, the energy which accumulated over two hundred years would be fully released, resulting in a super strong earthquake of magnitude 9.

Dr. Chuan-Chou Shen also pointed out that, according to their measurements of the last four cycles, the 8.4 earthquake which took place on Mentawai Island last year was the beginning of a cluster of large earthquakes. If the pattern of tectonic movement remains unchanged, he estimated that every 6-13 years the region would see an earthquake happening on 7-8 scale, whereas the super strong earthquake would happen in another thirty years. Such strong seismic activity could trigger tsunamis which could directly endanger the lives and properties of the citizens of Southeast Asian countries, resulting in incalculable losses. Therefore, Dr. Shen emphasized that South Asian and neighboring countries should stay highly alert, implement safety measures and disaster relief measures. Taiwan should also pay attention to disaster prevention measures and real time reporting system.

Dr. Shen's research project was subsidized by the National Science Council, and guided by Dr. Ching-Hua Lo, Dean of the College of Sciences. The research team members spent years conducting research on the coral reefs in Pacific Ocean, South China Sea and the Indian Ocean. Their painstaking efforts paid off and they made a breakthrough in the coral dating technology that remains unrivalled in the world. That Dr. Shen and his research team were able to reconstruct the earthquake cycle which took place on Mentowai Island since the 14th century was not only a great achievement in earth science, but also an excellent contribution to humanity. For Dr. Shen's research article please consult December 12th issue of "Science": Science, 2008, Vol. 322, Issue 5908, Bicentennial earthquake supercycles inferred from sea-level changes recorded in the corals of West Sumatra.

For detailed information on Uranium Thorium Coral Dating Technology please consult "Geochemica et Coscochimica Acta": Shen, C.-C., Li K.-S., Sieh K., Natawidjaja D., Cheng H., Wang X., Edwards R. L., Lam D. D., Hsieh Y.-T., Fan T.-Y., Meltzner A. J., Taylor F. W., Quinn T. M., Chiang H.-W., and Kilbourne K. H., 2008. Variation of initial 230Th/232Th and limits of high precision U-Th dating of shallow-water corals. Geochim. Cosmochim. Acta, 72, 4201-4223.

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