Among the 18 monitoring wells, eight observation wells were
adopted in the analysis due to their high sensitivity to earthquakes.
From the monitoring data, the groundwater level variations triggered
by earthquakes can be detected only for earthquakes with
magnitudes greater than 4.0. Therefore, a total of 21 earthquake
events with Richter scale magnitudes greater than 4.0 that
occurred from 2003 to 2004 were collected and analyzed. The
earthquake events are shown in Table 1. The earthquake times
are the local times in Taiwan (GMT + 8). The earthquake magnitudes
used in this paper are Richter scale magnitudes (local earthquake
magnitude, ML) provided by the Taiwan Central Weather
Bureau (TCWB). The locations of the eight wells and the epicenters
of the 21 earthquake events are shown in Fig. 2. Twenty of the
earthquakes occurred in the eastern region of Taiwan or in the
sea and one occurred in the western part of Taiwan. This distribution
is due to Taiwan being west of the Pacific Ring of Fire, with the
plate boundary in the eastern part of Taiwan.