以到時比序法及微型地震網改進臺灣低價位地震預警系統

Abstract

由於至今仍然沒有可靠的方法預測地震，因此現階段對於地震的防災機制，主要著重於建物的耐震設計，地震預警(Earthquake Early Warning, EEW)則是另一項有效的即時防災方法(Kanamori et al., 1997)。地震預警需要在短時間內提供可靠的地震資訊，因此，如何改進訊號處理的方法與流程，在更短的時間內得到更可靠的預警報告便是個相當重要的課題。國立臺灣大學地質科學系地震學實驗室利用Palert感測器於全台灣架設了高密度的低價位地震預警系統(Wu at al., 2013; Wu and Lin, 2014)，希望藉由密集的測站分布在地震初期快速提供地震定位與規模預估。由於地震初期偵測到震波的測站數偏少且分布不均，該系統需要利用超過8個測站才能提供較穩定的資訊，然而等待較多的測站訊號卻會降低地震預警的處理時效性。因此，本研究利用1981年Anderson提出的到時比序定位法(Arrival-time order location method)改進Palert系統的定位與預警成效。同時因為Paler 儀器本身的訊噪比偏低的問題，導致不需要震源距參數的τc (Kanamori, 2005, Wu and Kanamori, 2005a)規模無法應用在Palert預警系統上(Wu at al., 2013)，本研究希望能藉由微型地震網的訊號疊加，改善上述問題，為現地預警提供τc規模預估。 測試的結果上，到時比序法可以在地震初期利用4到5個測站即讓定位及地震規模的預估達到可靠的水準，改善預警時效；利用微型地震網亦能夠成功預估比單站Palert更準確的Mτc規模。

Since there is no practical method for earthquakes prediction today, the main disaster prevention method is based on the seismic design of buildings. Earthquake early warning (EEW) is another effective way to reduce damage in real-time (Kanamori et al., 1997). Because EEW needs to provide reliable message in a short time, it is important to shorten the reporting time window by the improving of data process. In order to provide location and magnitude after an earthquake just happened, a low cost and high density EEW system has been developed and established by using the Palert seismometers in Taiwan (Wu et al., 2013). Due to the distribution of the stations, which detected the signals at first, is poor. It needs more than eight stations to get reliable information. Thus, it shortens the lead time before strong ground shaking. This study use the arrival-time order location (AOL) method, which introduced by Anderson in 1981, to improve the efficiency of Palert EEW system for earthquake location. At the same time, because of Palert has a relatively low signal-to-noise ratio (S/N) in τc (Kanamori, 2005, Wu and Kanamori, 2005a) determinations. So τc approach does not use in the Palet EEW system (Wu et al., 2013). This study try to use the signals stacking small arrays to enhance S/N ratio and try to use τc for magnitude estimation. Results shows that, AOL method can provide a reliable earthquake location by only using four to five stations. It can improve the EEW efficiency. By stacking the signals from small array can also get more accurate magnitude estimation usingτc. So that more information can be provided in on-site EEW warning purpose.