Analysis of the Response Mechanism of Confined Aquifer Well Water Level System to Bulk Strain

Abstract

AbstractBased on principles of viscoelastic mechanics and hydrostatics, this paper expounds the dynamic mechanism of bulk strain response to exterior forces in the confined aquifers and derives the theoretical formula of well water level observation system, which shows that the system is an amplification link at zero order and its transfer function is a constant, then figures out the theoretical scale unit value range allowed in the well water level system with the porosity of aquifers equivalent to zero or 1. Considering that the system is a natural bulk strain gauge, the amplitude ratio (tidal factor) derived by the Venidikov harmonic analysis can be regarded as the transfer function (sensitivity) of a well. Owning to that the semidiurnal wave is the major object of well water level observation and M2 wave constitutes the majority of semidiurnal waves, it is advisable to take the reciprocal sensitivity of M2 wave as the scale unit of a well water level system. On this basis, the paper utilizes the well water level minute‐values at 5 Fujian wells in May 2008 to compute the coseismic striking steps caused by Wenchuan M8.0 earthquake, and the result show that the amplitude of the coseismic steps and the bulk strain earth tides reach to the same order of magnitude as much as 10–7 ~ 10–8.