A study on the mechanism of water well resonance induced by pre-earthquake signals

• Main Authors: Chun-Hsiang Wang, 王俊翔
• Other Authors: 黃良雄
• Format: Others
• Language: zh-TW
• Published: 2006
• Online Access: http://ndltd.ncl.edu.tw/handle/97978437297986796172

碩士 === 國立臺灣大學 === 土木工程學研究所 === 94 === One day before the drastic 921-earthquake at central Taiwan in 1999, the pre-earthquake signals were observed in some water wells in Tsuo-Shui River water basin. How could the unusual tiny pressure wave of the pre-earthquake signals be observed? We believe one of the possible reasons is due to the effect of resonant amplification of wells. In this study, we expect to analyze the physical mechanism which leads the occurrence of resonant phenomenon by the construction of mathematical model. In the assumption that the water in the well is incompressible, inviscid and irrotational homogeneous ideal fluid and that outside the well is porous-media fluid with rigid structure, the small amplitude wave theory and Darcy’s law are adopted in the present study to investigate the wave field and the physical mechanism when the tiny pressure wave of the pre-earthquake signals is acting on the well. We consider the wave number of the tiny pressure wave of the pre-earthquake signals passing through confined aquifer as that of the second kind of dilational wave in Biot(1962) theory to which Huang & Song(1993) referred. The present study derives the reasonable boundary conditions, and thus constructs the boundary value problem by theoretical analytic method. Then by regular perturbation expansion method, dividing method and orthogonal condition of orthogonal functions, this study successfully solves the analytic solutions which correspond to physical phenomenon, and gets formulas of relative parameters which induce to resonance phenomenon. Instead of the result of the research similar to U-tube by Cooper(1965), longitudinal wave resonance of water in the well induced by huge longitudinal pressure wave, and that from traditional harbour resonance analysis, transverse wave resonance induced by huge transverse mass flux wave, in the study, we get a new result of resonance; i.e. resonance of transverse wave induced by tiny longitudinal pressure wave of the pre-earthquake signals. Due to the success of solving pre-earthquake signals acting on the well, the present study is helpful in analyzing well resonance and designing of observing water wells as the earthquake alert system.