| Summary: | 博士 === 國立交通大學 === 土木工程系所 === 101 === The temporal gravity changes in Taiwan are used to examine the crustal deformation in Taiwan. All gravity observations are corrected by the environmental effects, such as solid earth tide, ocean tide loading, polar motion, atmosphere and underground water. This study will put a special emphasis on ocean tide loading. Ocean tide loading(OTL) effect of gravity is large in Taiwan and around its nearby area. Three different OTL models are tested to improve the accuracy of absolute gravity around the coast of Taiwan and its islets. The model SGOTL with the latest regional ocean tide model of Taiwan is assimilated with local tide gauge records. In Taiwan, OTL10 and the high resolution DEM result in the optimum accuracy in the OTL corrections of absolute gravity measurements. It’s obviously to shown the standard deviations of adjusted gravity have reduced by using mixed method of ladder and star. Two major relative network campaigns around the whole Taiwan are made from 2003 to 2007. The relative gravity observations are adjusted using the weight-constraint least-squares method. With the 4-year gravity changes, we have found that orogeny occurs on the central ridges and land subsidence occurs in southwestern Taiwan with average rates of -0.085 mgal/year and 0.061 mgal/year, respectively. A gravity network in the Yunlin County in western Taiwan is established to determine gravity variations caused by large land subsidence. At station TAES, the gravity change rate from absolute measurements by FG5 is 22.72 μgal/year. The gravity-height admittance factor in Yunlin subsidence area is -5.25 μgal/cm, instead of -1.97 μgal/cm, due to the complicated mechanism of subsidence. This result can be a prototype method of subsidence monitoring by gravimetry.
|
|---|
