Coseismic response of water level in Changping well, China, to the Mw 9.0 Tohoku earthquake

- The amplitudes and periods of water level is well related to the vertical velocity.
- The fluctuation periods of water seismic wave is basically within 15-35 s.
- The water level fluctuation presents the gradual enhancement of aquifer permeability.
- The step rise of water level is related to the enhancement of aquifer permeability.
- The aquifer permeability rises by 6.56 × 10−14 m2 after the action of seismic wave.

SummaryA water-level meter installed in Changping well, China, recorded coseismic fluctuations and a step change induced by the Mw 9.0 Tohoku earthquake of 11 March 2011. Here we analyse the correlation between water level in the well and vertical ground motions recorded at a nearby surface site, and we examine the relationship between the characteristics of these two datasets and the well-aquifer system parameters. During the arrival period of P- and S-waves, the water level provides information about the intensification of high-frequency ground motions. During the arrival period of the surface waves, the amplitude of water-level fluctuations was closely related to the velocity of vertical-component surface motions. The fluctuation periods of these two parameters are in the range 15-35 s, and the period of oscillation displays a large-to-small characteristic behaviour. The amplification effect on the water level in Changping well, driven by the pressure fluctuation induced by the surface wave, was relatively small, but a low-to-high characteristic is apparent during the coseismic period, related to the gradual enhancement of aquifer permeability due to the action of seismic waves. The coseismic step increase in water level was related to the enhancement of aquifer permeability under the action of seismic waves, and the results of an inversion of water-level tidal-response characteristics show that permeability increased by ∼6.56 × 10−14 m2 in the vicinity of Changping well in response to the action of seismic waves emanating from the Tohoku earthquake.