Numerical Simulation of Groundwater Level Changes due to the Ocean Tide and the Earthquake

• Main Authors: Ding-Qian Zheng, 鄭丁乾
• Other Authors: Yeeping Chia
• Format: Others
• Language: zh-TW
• Published: 2016
• Online Access: http://ndltd.ncl.edu.tw/handle/86071064869533535767

碩士 === 國立臺灣大學 === 地質科學研究所 === 104 === Ocean tide may change the groundwater level in the coastal area. The Dongshi groundwater level monitoring station is located about 400 m from the shoreline. The groundwater level of Dongshi-3 and Dongshi-4 wells usually changes with ocean tide, but about 40 minutes behind it. The variations of groundwater level in response to the loading of ocean tide are related to the aquifer properties, such as elastic constants of sediments. The time lag is influenced by both the elastic constants and the hydraulic parameters. On the other hand, the co-seismic groundwater level change in the two wells induced by the Chi-Chi earthquake was attributed to the short-term loading from the lateral direction. In order to understand stress mechanism in Dongshi station, the finite element software ABAQUS was used. We established a two-dimensional simplified model and used tidal method to calculate the Young''s modulus of two aquifers where Dongshi-3 and Dongshi-4 are screened. Numerical analysis result revealed the Young’s modulus of Dongshi-3 and Dongshi-4 wells were 4.7×107 and 3.0×107 Pa ,respectively the hydraulic conductivities of Dongshi-3 and Dongshi-4 wells were 5.0×10-3 and 5.5×10-3 m/s. After the aquifer parameters were obtained, the amount of co-seismic groundwater level change induced by Chi-Chi earthquake could be calculated. The simulated co-seismic groundwater level changes were compared with the field observations, and the displacement at Dongshi area was found to be 0.01% of the model. Therefore, numerical analysis is a method that can be used to identify the aquifer parameters and earthquake effects.