In search of earthquake precursors in the water-level data of 16 closely clustered wells at Tono, Japan

Water-level data recorded during 1989-1999 at 16 closely clustered wells near the Tone mine in central Japan are searched for possible premonitory changes before earthquakes. The results suggest that some water-level drops at a sensitive well before an M5.8 local earthquake on 1997 March 16 and some large distant earthquakes during 1994-1995 in Japan may have been premonitory in nature. The high sensitivity of this well to earthquake occurrence is attributed to the near-critical hydrological conditions and the relatively high permeability of the tapped aquifer.