Thu, Mar 28, 2019 page2

• Study on crustal changes after 921 quake unveiled

  SEISMIC CYCLES: Taiwan has many mountains higher than 3,000m, but it is not yet clear how they arose from the Earth’s crust and the study could offer clues

  • By Lin Chia-nan / Staff reporter
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  Academia Sinica geoscience researchers yesterday unveiled a study that used GPS data to track the nation’s crustal changes following the 921 Earthquake in 1999, to shed more light on the creation of mountains and seismic cycles.

  The magnitude 7.3 earthquake occurred on Sept. 21, 1999, in Nantou County’s Jiji Township (集集), leaving 2,456 people dead and destroying thousands of buildings.

  Subterranean rocks at a depth of 20km had stabilized one year after the quake, but deeper layers might be still changing very slowly today, Academia Sinica Institute of Earth Sciences researcher Hsu Ya-ju (許雅儒) said.

  

  Academia Sinica Institute of Earth Sciences researchers Hsu Ya-ju, right, and Tang Chi-hsien in Taipei yesterday present their study into geological changes following the 921 Earthquake.

  Photo: Chien Hui-ju, Taipei Times

  While GPS data has been used to study fault lines in previous studies, the team developed a new method of using such data to model geographical changes from the Earth’s surface to subterranean layers 50km in depth without having to make a lot of hypotheses, she said.

  The study extends from a master’s thesis written by Tang Chi-hsien (唐啟賢) in 2016, when he was studying at National Central University, Hsu said.

  Tang, 27, is serving alternative military service by doing research at the institute and plans to return to National Taiwan University to complete his doctoral degree.

  Hsu and Tang worked with University of Southern California professor Sylvain Barbot and Nanyang Technological University professor James Moore to study GPS data about crustal changes collected over 14 years following the quake.

  Taiwan has many mountains higher than 3,000m, but it is not yet clear how they arose from the Earth’s crust and the team’s study could offer some clues, Tang said.

  Tang grew up in Hualien, where earthquakes are frequent, and that motivated him to research seismic activity, he said.

  The team detailed their findings in a paper titled “Lower-crustal rheology and thermal gradient in the Taiwan orogenic belt illuminated by the 1999 Chi-Chi earthquake” which was published in the journal Science Advances.

  The team’s findings are also useful for other nations, as rock strata in different nations share common features, institute director Chung Sun-lin (鍾孫霖) said.

  To commemorate the 20th anniversary of the 921 Earthquake, the Taiwan Earthquake Research Center is to hold an international conference in September, Chung added.
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