ABSTRACT




We proposed an effective approach to improve the accuracy of offshore earthquake location in the earthquake early warning (EEW) system of Taiwan. The EEW system was built upon Geiger’s method for earthquake location that requires a set of initial estimates (epicenter, depth, and origin time). Because the initial epicenter highly depends on the locations of inland stations, for far offshore events the final solution falls effortlessly into a local minimum which may far away from the actual position. To solve this problem, an approach for choosing a better initial epicenter was proposed. We added predefined initial epicenters on the offshore area and then implemented several programs running Geiger’s method simultaneously. Each of the programs adopted a different predefined initial epicenter. The best earthquake location is given by the most timesaving run, assuming that the solution is converged most efficiently related to the closest distance between the initial and true epicenters. The modified method has been tested with the online EEW system from June 2016 to July 2017 for offshore east Taiwan. A total of 60 earthquakes with magnitudes ranging from 3.3 to 6.0 were detected successfully. The results were compared with the estimations from the original EEW system, showing that our proposed method for offshore earthquakes is able to reduce location error by about 4.9 km on average.


Earthquake Early Warning System in Taiwan

·                         Authors
·                         Yih-Min Wu
·                         Nai-Chi Hsiao
·                         Tai-Lin Chin
·                         Da-Yi Chen
·                         Ya-Ting Chan
·                         Kai-Shyr Wang
First Online: 14 October 2014
DOI: https://doi.org/10.1007/978-3-642-36197-5_99-1

Introduction


Taiwan is located on the plate boundary where Philippine Sea Plate collides with Eurasian Plate with a very high plate convergence rate of 8.0 cm/year (Yu et al. 1999; Fig. 1). Nearly 18,000 seismic events occur around Taiwan and the vicinity every year (Wu et al. 2008). Some of the destructive earthquakes caused large casualties, such as the 1906, M L = 7.1 Meishan earthquake (1,258 death); the 1935, M L = 7.1 Hsinchu-Taichung earthquake (3,276 death); and the 1999, M L = 7.3 Chi-Chi earthquake (2,455 death). Earthquake is one of the most serious disasters in Taiwan. Therefore, it is important to seek scientific resolutions to alleviate earthquake hazards.

































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https://link.springer.com/referenceworkentry/10.1007%2F978-3-642-36197-5_99-1

Taiwan earthquake alert system saves lives

Publication Date: September 08, 2013
A warning sound, the magnitude of a predicted earthquake and its estimated arrival time were broadcast across the campus of Gang Ping Primary School in southern Taiwan’s Chiayi City seconds before a magnitude-6.5 earthquake jolted Yuchi Township in Nantou County June 2.
The earthquake early warning system was developed by the Central Weather Bureau, National Center for High-performance Computing, National Center for Research on Earthquake Engineering and National Science and Technology Center for Disaster Reduction under an NT$30 million (US$1.01 million), three-year project beginning 2009.
Such systems as the EEWS are crucial for Taiwan because the nation, situated on the circum-Pacific seismic belt at the junction of the Manila and Ryukyu trenches along the west side of the Philippine Sea plate, experiences frequent earthquakes. One of the most catastrophic natural disasters in decades to date was the magnitude-7.3 earthquake that struck Nantou in central Taiwan Sept. 21, 1999, resulting in 2,415 deaths and over 11,300 injuries.
The system was designed to reliably predict the occurrence of earthquakes with enough time to issue warnings and enable people to take precautions, NCREE researcher Lin Pei-yang said. “Seismic activity includes P and S waves. The P arrives faster than the S, with the latter more destructive and causing the collapse of buildings.
“If we can predict the arrival of the S and initiate early warnings, along with staging regular drills, we can mitigate the impact of the quake on life and property.”
In fact, the monitoring of earthquakes in Taiwan began during the Japanese colonial occupation of the nation between 1895 and 1945, with equipment used over the century advancing from traditional instruments like the Gray-Milne seismograph, which was limited to analog recording and low magnification of shockwaves, to highly sensitive electromagnetic seismographs. The Taiwan Telemetered Seismographic Network and the CWB Seismic Network were launched respectively in the 1970s and 1980s to facilitate understandings on plate movements.
The CWB also implemented a series of the Taiwan Strong Motion Instrumentation Program beginning in 1992 in hopes of increasing knowledge of earthquakes.
To date, over 700 strong-quake and 100 real-time monitoring stations have been set up nationwide. But solely observing the occurrence of earthquakes cannot substantially help reduce the damage caused by plate movements, so seismic activity research institutions across the world have moved to develop EEWSs, including Japan, from whose system Taiwan’s is based.
According to Liu, Japan Meteorological Agency launched its EEWS system in October 2007. The earthquake monitoring stations, situated every 20 kilometers, as well as rapid computerized calculations of the location and transmission of waves, are key to issued warnings. Once the tremors, or the P waves, are detected and the information calculated, a warning will be issued and disseminated to the public via the broadcast media.
The Japanese system gives citizens a 30 to 50 second warning in advance as most of temblors strike further off the coast than in Taiwan and travel 100 to 200 kilometers to reach such cities as Tokyo and Kyoto, Liu said. In Taiwan, the EEWS allows at most a 10 second warning as the nation experiences seismic activity that take place closer to the island, such as the one in Nantou 14 years ago.
To complement Taiwan’s warning system, Liu said a program has been initiated to teach students on the first floor of a building how to reach open ground in 15 seconds, while those on the second and third floors are instructed to protect their heads with their hands or schoolbags and crouch beside chairs.
Mostly targeted at schools for the time being, the program is only useful when people know how to react immediately upon receiving the warning, he said, adding that training is crucial in order to ascertain that users can benefit in such limited time for reaction.
“Once the students are trained, it will be easier to introduce the system to households.”
The NCREE researcher said that in addition to Gang Ping Primary School, the warning system operates at National Chung Cheng University in Chiayi County; Yu-dong Junior High School in Hualien County; Hualien Train Station; Fanghe Junior High School in Taipei City; Guang Fu Elementary School and Yilan Elementary School in Yilan City; and Nanan Junior High School and Luodong branch of security firm Taiwan Secom Co. Ltd. in Yilan County.
“Installed 2 meters below ground at Gang Ping Primary School, the system’s location is designed to prevent student movement from interfering with sensitive seismic activity monitoring equipment,” Liu said.
As well as the audible tone, warnings were displayed on light-emitting diode, or LED, signs in the school 15 seconds before the quake struck, while messages concerning the tremor were also texted to the teachers and principals, he said.
“LED signs are faster compared to televisions as the latter needs three to five seconds to be turned on, whereas text messages are sent to all school faculties because the principal may not be on-site to handle the situation.”
Going forward, Liu said, his institution hopes that the warning system can be installed in a further 84 schools nationwide and may even work with firms in transferring the technology to develop customized EEWS, further reducing the damage caused by earthquakes. (JSM)
Write to Grace Kuo at mlkuo@mofa.gov.tw 
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