The response of well-aquifer systems to seismic waves

The degree to which the water level in an open well fluctuates in response to a seismic wave is determined by the dimensions of the well, the transmissibility, storage coefficient, and porosity of the aquifer, and the type, period, and amplitude of the wave. The water level responds to pressure-head fluctuations due to dilatation of the aquifer and to vertical motion of the well-aquifer system; hence a wave that produces either of these can cause the water level to fluctuate. However, the response to dilatation is much larger than the response to vertical motion. A solution is derived for the nonsteady drawdown in the aquifer due to a harmonic motion of the water level. This solution is then used in the equation of motion of the water column to derive expressions for the amplification, which is defined as the ratio χ0/h0 (for oscillation due to dilatation) or the ratio χ0/a (for oscillation due to vertical motion of the well-aquifer system), where χ0 is the amplitude of water-level fluctuation, h0 is the amplitude of pressure-head fluctuation, and a is the amplitude of vertical motion of well-aquifer system. Amplification curves are given for differing well dimensions and aquifer constants.