| 摘要: | 為了研究台北地區之地表形變及其與山腳斷層和大屯火山群活動的關聯性，本研究蒐集2006年至2010年間由中央地質調查所、中央研究院地球科學所、內政部及中央氣象局在台北地區設置的29個GPS連續觀測站觀測資料來探討台北地區之地表變形。本研究使用GAMIT/GLOBK軟體及解算各測站在ITRF2005框架下之座標、速度及GPS時間序列資料，並濾除因地震和更換儀器等因素造成之影響。此外，本研究還利用空間濾波技術處理時間序列，改善時間序列中測站共同誤差之影響量，降低其離散程度。接著，GPS時間序列的分析結果顯示，其雜訊較接近「白噪音＋閃爍雜訊」的模式。藉由最大概似法估算雜訊的振幅大小，修正其在時間序列造成之影響，進而求得較可靠之速度值及其誤差，以此結果計算地殼應變率之空間變化。本研究結果顯示，相對於澎湖白沙GPS觀測站（S01R），台北地區的水平速度場約2.0?5.1 mm/yr，速度場的方位角之分布從N5 E至N75 E，呈現順時針往東南旋轉之趨勢。此外，本區域中大部分的主軸應變為西北－東南向之伸張應變，平均主應變率為0.17±0.01 μstain/yr，僅在局部地區呈現壓縮應變；而在山腳斷層上的平均主應變率為0.03±0.05 μstain/yr。此外，本研究結合了GPS、永久散射體差分干涉影像（PSInSAR）及水準測量的結果來探討台北地區的垂直變形，結果顯示在西部麓山帶、大屯火山群和林口台地有1 ~ 2 mm/yr的抬升量，而台北盆地中心相對於邊緣則是出現下降的趨勢，最大下陷速率可達5 mm/yr，而造成台北盆地西緣持續下陷有兩個因素，一個是淺部地層的壓密，另一個則是盆地西緣的山腳斷層之活動。以上為本研究之結果，希望能提供作為近期台北盆地地區地表變形的解釋，並有助於台北盆地都會區之地質災害評估與預防分析。 This study used 5 years of continuous GPS observations of 29 stations in the Taipei region and of 9 GPS constrained sites around Taiwan, along with other 11 IGS sites in the Asian Pacific region, to calculate the coordinates and velocities of each site and to obtain the time series of station positions under the ITRF2005 reference frame. The GAMIT/GLOBK software was employed, and influences of earthquakes and changing instruments were evaluated and removed. Furthermore, we reduced the common-mode errors by using the spatial filtering technique to improve the scattering in the time series. In order to accurately estimate velocities and their uncertainties, noises have to be evaluated using more realistic model. I estimated the power spectral index of time-dependent noises of GPS stations in Taipei Region, and found the spectral index are -0.59, -0.52, and -0.45 for N, E, U components, respectively. This result indicates the noise of GPS time series are best described as a combination of white noise and flicker noise. Amplitudes of these noises were estimated by using the maximum likelihood method. The corrected secular velocities and their uncertainties were used to evaluate crustal kinematic behaviors such as principal strain rates, dilatation rates, shear strain rates, and rotation strain rates. Results show that the horizontal ground motion of the Taipei Basin area is about 2.0~5.1 mm/yr in direction of N5 E to N75 E, relative to the Paisha GPS station (S01R) at Panghu, which was considered as a stable continental margin station. Moreover, a NW-SE extension strain rate of about 0.03±0.05 μstrain/yr is measured in an area of 574 km-wide across the Shanchiao fault. Consistent with previous measurements of Permanent Scatter Interferometric Synthetic Aperture Radar (PSInSAR). our GPS data revealed vertical deformation in the northern Taiwan including: (1) a slight uplift about 1~2 mm/yr in the Western Foothills, the Tatun volcano group and the Linkou Tableland, and (2) the subsidence about 2~5 mm/yr around the Taipei Basin. Local substantial subsidence in the Taipei Basin can be distinguished by combined effects from the compaction of shallow sediments and the activity of Shanchiao fault. |
