利用高密度低價位地震網決定同震變形與破裂方向;Estimations of Coseismic Deformation and Rupture Directivity with a Dense Low-Cost Seismic Network

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题名:	利用高密度低價位地震網決定同震變形與破裂方向;Estimations of Coseismic Deformation and Rupture Directivity with a Dense Low-Cost Seismic Network
作者:	詹智丞;Jan, Jyh Cherng
贡献者:	地球科學學系
关键词:	高密度低價位地震網;同震變形;地震破裂方向;a Dense Low-Cost Seismic Network;Coseismic Deformation;Earthquake of Rupture Directivity
日期:	2019-01-23
上传时间:	2019-04-02 14:29:31 (UTC+8)
出版者:	國立中央大學
摘要:	自2012年起，臺灣大學地震預警團隊開始大規模在臺灣各地廣佈微機電系統加速度儀的高密度低價位地震網，以P波初動警示的概念名為P-Alert，截至2018年12月已有692站，這些測站提供豐富的即時資料，近年來促進許多科學研究與實際應用，而在本研究中，除原始P-Alert地震預警的宗旨外，並將其地震網能力延伸至同震變形位移量與地震破裂方向性之偵測兩方面。在同震變形位移量研究中，先進行P-Alert資料之前處理，將資料還原成尚未套用動態平均演算前的狀態，之後利用自動基線修正方法，始獲得同震變形位移量，選擇過去ML >6的地震事件，比較從P-Alert網與臺灣強地動觀測計畫(TSMIP)加速度儀，以及全球定位系統(GPS)的同震變形位移量，發現當位移量大於2 cm時，P-Alert提供可信賴的數值，這說明低價位地震網亦可近即時的提供防救災的關鍵資訊。在地震破裂方向性研究中，利用P-Alert近場(<25 km)即時強地動速度資料來即時的判識地震破裂方向性的資訊，並對遠方提供強地動預警。此方法建構在即時震度圖的內插方法與方向性的衰減回歸分析上。由16個臺灣與美國加州中到大型規模地震事件的分析，顯示在17秒後可獲得穩定結果，而該結果也與過去研究相符；此外，本研究亦提供破裂方向性放大強度的指標，在臺灣地區，ML≥6地震皆普遍有顯著的方向性效應。因此，P-Alert近即時方向性訊息可增進地震預警系統能力，並提供遠方更準確的強地動預估。 ;Since 2012, the earthquake early warning (EEW) research group at the National Taiwan University has widely deployed a dense seismic network based on micro-electro-mechanical system (MEMS) P-wave-alert-device (P-Alert) accelerometers, namely P-Alert network in Taiwan. The total number of stations is up to 692 until December 2018, and the network has provided abundant real-time data to facilitate many successful research studies and applications in recent years. Here, in addition to the original purpose of earthquake early warning, we extend the P-Alert network applicability to two new aspects: coseismic deformation (Cd) estimation and near-real-time earthquake rupture directivity determination. For the Cd estimation, we select the data of ML>6 earthquakes of P-Alert network to process. Using a data preprocessing scheme to recover the dynamic average embedded within the P-Alert data, we adopt an automatic baseline correction approach for the accelerograms to determine the Cd values. Comparing the Cd values from P-Alert, the global positioning system (GPS), and the Taiwan Strong Motion Instrumentation Program (TSMIP) network, the P-Alert network can provide the reasonable estimation when Cd value greater than 2 cm in near-real-time, which offers crucial information for seismic hazard mitigation and demonstrates the ability of low-cost MEMS system. For the near-real-time earthquake rupture directivity determination, we estimate directivity information using near-field (<25km) real-time ground motion accelerograms from P-Alert and provide warning for far-field regions. The method is based on real-time shaking map interpolation and directional attenuation regression analysis. For the 16 moderate-to-large magnitude earthquakes in Taiwan and California, the results can be obtained stably within 17 s and are consistent with previous studies. We also propose an indicator of the strength of directivity ampliﬁcation that shows a prevalence of strong directivity effect for ML≥6 earthquakes in Taiwan. Such near-real-time directivity information is therefore useful for earthquake early warning systems to provide more accurate ground shaking alerts for the far-field areas where the strong shaking has yet arrives.
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