微地動特性的研究及應用; Study and Application of the Microtremor Characteristics

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题名:	微地動特性的研究及應用;Study and Application of the Microtremor Characteristics
作者:	郭俊翔;Chun-Hsiang Kuo
贡献者:	地球物理研究所
关键词:	微地動;速度剖面;單站頻譜比;聯合逆推法;場址分類;microtremor;joint inversion;HVSR;site classification;Vs30;Vs profile
日期:	2009-06-16
上传时间:	2009-09-22 09:56:06 (UTC+8)
出版者:	國立中央大學圖書館
摘要:	微地動量測正逐漸地被應用在場址放大效應的評估，以及剪力波速剖面之推求上。然而，微地動的組成成份仍舊是一個未解且有爭論的議題。中村豐教授提出單站頻譜比法並主張微地動單站頻譜比於主頻的放大效應主要是由多重反射的SH波所構成，而非被大多數學者所認為的雷利波。本研究亦透過幾項有力的證據證明中村豐教授之理論：（1）雷利波橢圓率之主頻放大倍率與微地動的單站頻譜比主頻之放大倍率在大多數情況下皆有很大的差距；相較之下，其與SH波的轉換函數之主頻放大率則相當近似；（2）相速度有時候會在主頻附近呈現不穩定的現象；（3）頻譜比之共振放大及凹下處之質點運動形態的差異；（4）雷利波的橢圓率無法模擬微地動頻譜比的雙主頻現象，而SH波轉換函數卻可以。然後，本研究建立了一個可以更精確的推求剪力波速剖面，同時又可以增加小型微地動陣列之解析深度至基盤的聯合逆推法，並採用此方法推求位於臺北盆地之七個強震站下的剪力波速構造。其中TAP089吳興國小微地動陣列各測點之單站頻譜比彼此之間有相當明顯的差異，因此對每一測點採用單站頻譜逆推法去求得此陣列下的三維速度構造。另外，本研究中也以複回歸法求得臺北盆地及宜蘭地區的剪力波速經驗式，並使用328個強震站的井測波速資料（井深皆30米以上）測試三種常用之波速外插法（最小平方法，統計法，底部常數法）。測試結果顯示底部常數法之精確性最佳，故採用此外插法推求井深未達30米之強震站的近地表30米內之平均剪力波速，並提出最新之台灣強震站的場址分類。 Microtremor measurement has been increasingly adopted to assess site amplification and S-wave velocity profile at sites. However, the composition of microtremor is still a debatable issue. Nakamura claimed that the resonant peak on the dominate frequency of HVSR of microtremor is mainly constructed by the multi-reflection of SH waves rather than Rayleigh waves. This study identified the theory via several evidences: (1) Large disparity on amplifications between ellipticity of Rayleigh waves and HVSR of microtremor; by contrast, disparity between SH transfer function and HVSR of microtremor is much smaller. (2) Phase velocities sometimes become unstable when near the dominate frequency. (3) The difference of particle motions of resonant peak and trough. (4) The ellipticity of Rayleigh waves can not simulate the double peak at a known site, whereas the SH-wave transfer function can. Hereafter, this study developed a joint inversion method to estimate S-wave velocity profiles more accurate and increase the detectable depth until bedrock for a small array. By using the technique, S-wave velocity subsurface structures were estimated at seven strong motion stations in the Taipei Basin. Furthermore, significant discrepancy was detected on each HVSR of TAP089, and then adopted the HVSR inversion to find the 3D subsurface structure beneath this array. Additionally, empirical equations for S-wave velocity in the Ilan area and the Taipei Basin were evaluated by relating the relation of S-wave velocity, N-value, and depth using a multivariable regression approach. Three extrapolations called LSS, STS, and BCV were examined in this study by using 328 DH, and the BCV is obviously the most accurate one. Therefore, a new site classification for TSMIP stations in Taiwan was proposed.
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