臺灣地區震源P波加速度特性之研究
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2017
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本研究使用複數解載(Complex demodulation)、波線追跡法(Ray tracing)與三維衰減構造(Attenuation structure)等方法，以中央氣象局強地動觀測計畫(Taiwan Strong Motion Instrumental Program ,TSMIP )臺中地區、臺南地區、宜蘭地區、花蓮地區與臺東地區測站地震事件記錄，解算震源P波加速度時間函數，為研究震源P波加速度時間函數之新解法。
本研究目標為震源P波加速度時間函數，選取芮氏規模(ML)大於6.0的地震事件，如此震波傳遞至測站方有足夠之初達P波加速度波形紀錄可供分析；並且各地區測站地震紀錄之地震強度大於4級，如此初達P波波形方足夠明顯供分析使用。
由臺中地區、宜蘭地區與臺東地區測站資料解算地震事件I之震源P波加速度時間函數結果可見，各地區解算同一個地震震源加速度變化一致，故推論本研究應為研究震源特性之可信方法。臺南地區測站解算地震事件I之震源P波加速度時間函數結果與其他地區測站解算結果比較可見其加速度變化相對較低，由此地區地下構造推論可能為沖積層造成之場址效應造成，然而更精確的原因尚待進一步的研究。
由宜蘭地區測站資料解算12個地震事件震源P波加速度時間函數，地震事件A-I的P波的震源時間函數具有高線性相關性，震央分布沿著宜蘭平原向東延伸至琉球溝與沖繩槽之間，在大地構造上屬於菲律賓海板塊與歐亞板塊碰撞隱沒區，於中央氣象局地震活動分區中屬於花蓮分區。事件J的P波加速度變化以較低的加速度變化率上升到最大值，並且以較低的加速度變化率下降，震央位於海岸山脈至花東海盆之間，在大地構造上屬於菲律賓海板塊與歐亞板塊弧陸碰撞區，於中央氣象局之地震活動分區中屬於臺東分區。事件K和L具有相似的P波加速度變化，具有高線性相關，震央位於臺灣本島中央，於大地構造上屬於板塊運動形成造山運動之陸地抬升區，於中央氣象局之地震活動分區中屬於臺中分區。
研究結果顯示不同分區之震源加速度時間函數具有不同加速度變化，可知各地區之孕震構造有不同的地震加速度特性，推論位於不同孕震區的震源可能具有不同的錯動過程，在應力釋放時以不同的加速度變化反應其差異。
This study uses complex demodulation, attenuation structure, and ray tracing to compute the source time function (STF) of P-wave acceleration based on the earthquake data recorded at the Taichung, Tainan, Yilan, and Taitung stations that are operational under the Taiwan Strong Motion Instrumental Program (TSMIP) of the Central Weather Bureau. Complex demodulation estimates the variation of acceleration with time at each frequency for the seismic records. The acceleration of source P-waves at each frequency are first calculated by determining the propagation path and travel time of seismic waves using ray tracing. Subsequently, the attenuation factor for each block in the three-dimensional attenuation structure traversed by the waves is computed using the propagation path. The acceleration of source P-waves is calculated based on the travel time, attenuation factors, as well as the data at each frequency. The STF of P-wave acceleration is calibrated by substituting the P-wave amplitude for each frequency into the source time function of acceleration, to obtain the STF of P-wave acceleration. The regional seismic results achieved using this method agree with the geotectonic features analyzed by the Central Weather Bureau. The reliability of the protocol developed in this study is therefore corroborated. Apart from velocity based methods, this study offers a different technique of accurately solving source time functions.
This study uses complex demodulation, attenuation structure, and ray tracing to compute the source time function (STF) of P-wave acceleration based on the earthquake data recorded at the Taichung, Tainan, Yilan, and Taitung stations that are operational under the Taiwan Strong Motion Instrumental Program (TSMIP) of the Central Weather Bureau. Complex demodulation estimates the variation of acceleration with time at each frequency for the seismic records. The acceleration of source P-waves at each frequency are first calculated by determining the propagation path and travel time of seismic waves using ray tracing. Subsequently, the attenuation factor for each block in the three-dimensional attenuation structure traversed by the waves is computed using the propagation path. The acceleration of source P-waves is calculated based on the travel time, attenuation factors, as well as the data at each frequency. The STF of P-wave acceleration is calibrated by substituting the P-wave amplitude for each frequency into the source time function of acceleration, to obtain the STF of P-wave acceleration. The regional seismic results achieved using this method agree with the geotectonic features analyzed by the Central Weather Bureau. The reliability of the protocol developed in this study is therefore corroborated. Apart from velocity based methods, this study offers a different technique of accurately solving source time functions.
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複數解載, 衰減構造, 震源P波加速度時間函數, complex demodulation, attenuation structure, P-wave acceleration source time function