Unexpected far-field hydrological response to a great earthquake

Hydro-Mechanical Coupling

“…This relation may be re-expressed as p = −B σ = −B K u , where K u is the undrained bulk modulus and the change of volumetric strain. Based on the B K u estimated from the pre-seismic amplitudes of the tidal responses of water level and volumetric strain, Wang and Barbour (2017) converted the coseismic (black, upper curve) in the Fuxin well in northeastern China, before and after the 2011 Mw9.1 Tohoku earthquake, Japan (modified from Zhang et al 2019) change in water level to a coseismic change of volumetric strain of −61 × 10 −9 , similar to the measured coseismic volumetric strain of −85 × 10 −9 (Fig. 3.2).…”

“…If, on the other hand, the pressure response occurs together with flow of pore water, the process is no longer undrained. Figure 3.3 shows a case of coseismic increase of water level (lower curve) in the Fuxin well, NW China, which occurred together with a coseismic increase of volumetric strain during the 2011 Mw9.1 Tohoku earthquake, Japan (Zhang et al 2019). The occurrence of a coseismic increase of water level together with a coseismic increase of volumetric strain suggests that the latter was caused by the coseismic increase of pore pressure, which can only be caused by the occurrence of coseismic flow.…”

“…Fig. 3.3Water level (blue, lower curve) and volumetric strain (black, upper curve) in the Fuxin well in northeastern China, before and after the 2011 Mw9.1 Tohoku earthquake, Japan (modified fromZhang et al 2019) …”

Epilogue

“…But how transmissivity may depend on the forcing frequency and what are the mechanisms that may produce such dependence are largely unknown. Recent advances in instrumentation and data storage have allowed the documentation of water level data from yearly to seismic frequencies (Shih 2009;Sun et al 2018;Zhang et al 2019b), and thus have greatly extended the time scale for quantitative analysis. This opens the door for investigating the frequency dependence of aquitard impedance.…”

Groundwater Level

“…Weingarten and Ge (2014), using 24 years of data documented at Devils Hole, Nevada, significantly expanded the 'global dataset' (Fig. 6.5); new data from Sun et al (2018) and Zhang et al (2019b) are added to this compilation .…”