台灣地區動態座標框架立之先期研究-台灣現今之地殼變形模式

Preliminary study for establishment of dynamic datum in Taiwan –Modern crustal deformation of Taiwan

為進行台灣地區動態大地基準建立之先期研究工作，本研究使用1995-2005年531個GPS水平速度場與2000-2008年1843個精密水準測量成果來建立並分析台灣地區現今之地表速度場模型。分析相對於澎湖白沙測站S01R之速度場顯示，水平速度場由東部海岸地區約70mm/yr向台灣西北海岸地區逐漸遞減至近乎無位移，並在台灣北部呈順時針旋轉型態，於台灣南部則略呈逆時針旋轉之型態。此外，台灣地區之垂直速度場顯示，約10-20mm/yr之抬升速率，主要發生在中央山脈與海岸山脈南部地區，最大抬升速率約為23mm/yr，其他地區如平原或盆地則主要顯示為沉陷。在台灣西南部平原地區因為人為抽水的關係導致其沉陷速率普遍大於20mm/yr，最大沉陷速率約為113mm/yr。接著，本研究將台灣區分為27個構造塊體並考慮21條活動斷層之滑移虧損速率，藉由三維塊體模型反演台灣水平速度場來估算各塊體與活動斷層之歐拉極位置、塊體運動速率、斷層長期滑移速率與斷層鎖定率，並最終建立台灣水平速度場模型。由於動態框架之建立仍需考慮更複雜之地殼變形行為，因此在後續之研究工作中，本研究團隊將會持續針對垂直速度場模型、主要地震同震位移模型與其震後變形模型之連結進行，並會與現行之TWD97@2010座標框架進行銜接，期能在不久的將來提出適合台灣之動態框架。 In order to establish the dynamic datum of Taiwan in the future, in this study we adopted 531 GPS horizontal velocities from 1995 to 2005 and 1843 precise leveling measurements from 2000 to 2008 to establish and analyze the present-day surface velocity model in Taiwan. The horizontal velocity field, relative to the station S01R, shows that the velocity of ~70 mm/yr in eastern coast gradually decreases to nearly no deformation in northwestern coast in Taiwan. In northern Taiwan, velocity field represents a clockwise rotation pattern, while a counterclockwise rotation pattern is revealed in southern Taiwan. Based on the vertical velocity field in Taiwan relative to the S01R, the uplift rate of 10-20 mm/yr is mainly observed in the Central Range and the southern Coastal Range with the maximum rate of ~23 mm/yr. On the contrary, the land subsidence is presented in other regions, such as the plains and basins, with the maximum subsidence rate of ~113 mm/yr. Next, we divided Taiwan into 27 tectonic blocks and 21 faults used to estimate the slip deficit. We inverted the Taiwan horizontal velocities for the locations of Euler poles, block motions, long-term fault slip rates, and fault coupling coefficients using the 3D block model. Finally, the horizontal velocity model in Taiwan is proposed based on the block modeling results. In order for establishing the dynamic datum of Taiwan, more complicated crustal deformation behaviors caused by earthquakes are needed be considered. Therefore we will continue working for the establishments of vertical velocity model, coseismic displacement models, and their following postseismic deformation models to propose a suitable Taiwan dynamic datum in the future. We will also try to apply the proposed dynamic model to the TWD97@2010 coordinate frame.

In order to establish the dynamic datum of Taiwan in the future, in this study we adopted 531 GPS horizontal velocities from 1995 to 2005 and 1843 precise leveling measurements from 2000 to 2008 to establish and analyze the present-day surface velocity model in Taiwan. The horizontal velocity field, relative to the station S01R, shows that the velocity of ~70 mm/yr in eastern coast gradually decreases to nearly no deformation in northwestern coast in Taiwan. In northern Taiwan, velocity field represents a clockwise rotation pattern, while a counterclockwise rotation pattern is revealed in southern Taiwan. Based on the vertical velocity field in Taiwan relative to the S01R, the uplift rate of 10-20 mm/yr is mainly observed in the Central Range and the southern Coastal Range with the maximum rate of ~23 mm/yr. On the contrary, the land subsidence is presented in other regions, such as the plains and basins, with the maximum subsidence rate of ~113 mm/yr. Next, we divided Taiwan into 27 tectonic blocks and 21 faults used to estimate the slip deficit. We inverted the Taiwan horizontal velocities for the locations of Euler poles, block motions, long-term fault slip rates, and fault coupling coefficients using the 3D block model. Finally, the horizontal velocity model in Taiwan is proposed based on the block modeling results. In order for establishing the dynamic datum of Taiwan, more complicated crustal deformation behaviors caused by earthquakes are needed be considered. Therefore we will continue working for the establishments of vertical velocity model, coseismic displacement models, and their following postseismic deformation models to propose a suitable Taiwan dynamic datum in the future. We will also try to apply the proposed dynamic model to the TWD97@2010 coordinate frame.