Frequency-dependent groundwater response to earthquakes in carbonate aquifer

Analysis of 12 years' groundwater level data (2007-2019) from a well in a carbonate aquifer in northern China reveals that the groundwater response to earthquakes may be dependent on frequency. While the coseismic permeability increased during the 2008 M7.9 Wenchuan earthquake and eventually recovered to pre-seismic values (similar to that reported in previous studies), the observed increase following the 2011 M9.0 Tohoku earthquake in the same well showed no such recovery. Analysis of the seismograms of the two earthquakes near the well shows that the dominant frequency of the Rayleigh waves was lower in the Tohoku earthquake by a factor of five, compared with that during the Wenchuan earthquake. We hypothesize that Rayleigh waves with lower frequency are more efficient in clearing clogs from larger fractures in carbonate aquifers, or the clogging in larger fractures in the given azimuth are more easily to be cleared to the seismic wave following the Tohoku earthquake, and that the cleared large fractures are difficult to recover with post-seismic groundwater processes.