| Summary: | 碩士 === 國立臺灣大學 === 地質科學研究所 === 106 === Global Positioning System (GPS) is widely used in studying seismic cycle deformation and plate tectonics. In Taiwan, we discover significant seasonal variation in GPS position time series and the seasonality greatly corresponds to hydrological cycle. In this study, we discuss the relation between the surface motion and seasonal water loading in southwestern Taiwan taking advantage of a dense spatial coverage of continuous GPS network. The annual GPS vertical deformation is mostly due to the elastic response to variations of surface loads in the wet and dry seasons, while some plain areas with massive water withdrawal are primary influenced by pore pressure effect. The seasonal vertical deformation on foothills is highly correlated to groundwater level, and is able to detect the occurrence of drought in the early 2010 and 2015 beforehand. We remove stations located in alluvial fan and estimate terrestrial water storage variation using a disk-load model with Green’s functions computed from an elastic earth model, PREM. We divide Taiwan into 0.2 by 0.2 grids and use seasonal GPS vertical displacements to invert the terrestrial water storage. In average, the inverted seasonal water variation is about 2 times larger in southern Taiwan compared to northern Taiwan due to heavy rainfalls during monsoons and typhoons in summer. Comparing soil moisture seasonal variation from GLDAS-Noah, GPS records integrated water storage variation including soil moisture, groundwater, reservoir etc. Consequently, GPS data from a dense array could be used as a tool to map the spatial variation of terrestrial water storage.
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