Fig. 5

a Examples of the three fitting functions. This graph shows the fitting results using the three functions for event 11; the logistic function (top), error function (middle) and decaying exponential function (bottom). The solid line indicates the fitting curve overlapping on the observed data (one-dot chain line) for each function. The differences between the observed data and the fitting curve are plotted for each function. b Fitting results of the decaying exponential function for the 11 events. This graph shows the fitting curves of the decaying exponential function (solid line) and the observed data (the one-dot chain line) for the 11 earthquakes from event 2 to event 12. The differences between the observed data and the fitting curves are plotted for each event. The amplitude of the groundwater level and fitting data are plotted at same scale for the all events