geographical location, pumping activity, leakage of precipitation, and seismic
sensitivity. Thus, the groundwater levels in the monitoring wells
are sensitive to stress/strain due to the installation requirements
of the monitoring well. The screens of the monitoring wells are
opened at various depths in the range of 84–294 mbeneath ground
surface. A 2-min sampling rate is adopted for the earthquake
groundwater monitoring system, which is much faster than the
1-h sampling rate for the groundwater resource monitoring wells
in Taiwan. The accuracy for groundwater measurement is up to
0.2 mm. A total of 18 wells were constructed around Taiwan initially.
They started to operate in 2003, at which point their capability
of detecting groundwater level anomalies triggered by
earthquakes was tested. The durations of observation data vary
with station due to the differences in the completion times of the
well installations. Locations of the observation wells are shown
in Fig. 1. More detailed information of the earthquake monitoring
wells is shown in the study of Lai et al. (2010)