Statistical Evaluation of Well Water Anomalies as Potential Precursors to Large Earthquakes

Abstract. Macroscopic anomalies such as well water fluctuations and unusual animal behaviour have been recorded in old documents and folklore accounts as possible earthquake precursors. However, no reliable earthquake prediction method based on such anomalies has ever been established. One of the reasons is that the same phenomena often occur independent of earthquakes. This study conducted a re-examination using shallow well water observation data recorded for eleven years by a volunteer observation network in Japan. While some critics have claimed that it was impossible to predict an earthquake using well water anomalies, especially shallow ones, the results suggest that some plausible anomalies may serve as true precursors. On the other hand, many anomalies were observed without associated earthquakes, and earthquakes without associated anomalies were also uncovered. The old documents and folklore may contain elements of truth, while unrecorded failures are hidden behind successful accounts. Credible anomalies were limited, and major earthquakes rarely occurred within the same focal region. Furthermore, maintaining systematic observations has been challenging. Even an eleven-year observation period was too short to empirically verify the feasibility of an earthquake prediction method for disaster mitigation. Therefore, continuous support is needed for empirical research on earthquake precursors.