竹子湖強震站場址效應之探討; Site Effect Analysis of the Chutzuhu Strong Motion Station

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题名:	竹子湖強震站場址效應之探討;Site Effect Analysis of the Chutzuhu Strong Motion Station
作者:	牟鍾香;JUNG-SHIANG MOU
贡献者:	應用地質研究所
关键词:	場址效應;site effect
日期:	2004-06-01
上传时间:	2009-09-22 09:58:41 (UTC+8)
出版者:	國立中央大學圖書館
摘要:	中央氣象局強地動觀測計畫（簡稱TSMIP）在陽明山設置竹子湖與鞍部兩個測站，其中，檢視竹子湖測站歷年來的地震紀錄，其最大加速度值均產生異常放大的現象，排除儀器故障的疑慮後，本研究以強震資料與野外微地動量測資料，並交叉運用單站頻譜比法以及雙站頻譜比法，探討竹子湖強震站場址效應，研究結果獲得以下結論： 1.分析1995?2002年間竹子湖強震站所收到的地震紀錄，無論地震特性為何，其主頻皆落在8Hz左右。而在時間域方面，以鞍部為參考點所得之PGA Ratio與地震規模、震央距、震源深度等參數進行討論，可能由於資料量不足，或與震源與路徑效應無關，無法歸納出任何結論。在頻率域方面，雙站頻譜比法之結果可以看出竹子湖測站場址效應放大的頻段落於8Hz?10Hz。 2.在設置竹子湖測站之15×7公尺見方草坪，進行17個密集微地動測點測量。分析各頻率之放大倍率等值圖，地震儀所放置的點位均屬於相對較大的放大倍率值，但是17個測點的第一主頻均落於5Hz?6Hz的頻段。此結果亦可以證明微地動量測對於小尺度的調查也有其可行性。 3. 本研究在距離竹子湖強震站20公尺處增設另一台ETNA強震儀，探討觀測坪局部場址效應。由雙站法可以看出，主要的放大頻帶落於10Hz左右之高頻區，呼應微地動測量所得到的第二峰值也落於此高頻區。經由淺層折射震測以及井下資料可以推論到草坪地下約存在著5公尺厚的低速鬆軟層，而地震儀放置在如此鬆軟低速區，造成竹子湖測站明顯的場址放大效應。 Both TAP056(Chutzuhu) and TAP066(Anpu) strong motion stations were installed in the Tatun area by Taiwan Strong Motion Instrumentation Program of CWB since 1992. It is discovered that unusual PGA value recorded at TAP056 over the years. In this study, local site effects are analyzed by using earthquake and microtremor survey data for understanding why TAP056 had this unusual phenomenon. First of all, we analyze the 18 earthquake records at TAP056 and TAP066 during the period from 1995 to 2002. In time domain, PGA ratios between TAP056 and TAP066 are: EW: 7.57±6.25, NS: 5.45 ±4.51, and V: 3.89 ±2.86. In frequency domain, dominant frequency recorded at TAP066 (rock site) varies with events. But for different earthquake events, dominant frequency at TAP056 is always located at around 8Hz. The spectra ratio of TAP056/TAP066 shows the amplification frequency at 8~10Hz. Second, we performed 17 microtremor measurements in the lawn which the TAP056 seismometer is located. According to the contour of the H/V Fourier spectrum ratio at different frequencies, we can see the position where the TAP056 is located higher than others. All of the microtremor measurements show the same dominant frequency at 5~6Hz. But only measured points near TAP056 station can found an amplified peak at around 8~10Hz. This result demonstrated that the microtremor measurements can be applied in small scale. Third, In order to check local site effect on this grassplot, we set up the other seismometer(056A) about 20 meters away from the grassplot. The spectra ratio of 056/056A also shows the amplification frequency at 8~10Hz. After the refraction survey, we can sure that the local back filled or top soft soil effects controlled the local site amplification at station TAP056.
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