**6. Conclusions**

Since July 2003, we have recorded three recurring radon anomalies (precursory to the 2003 *Mw* = 6.8 Chengkung, 2006 *Mw* = 6.1 Taitung, and 2008 *Mw* = 5.4 Antung earthquakes) at well D1, located at the Antung hot spring. The local geological conditions near the Antung hot spring with well D1 situated in a fractured aquifer surrounded by ductile mudstone and the in-situ volatilization of groundwater radon were attributed for causing the recurrent radon anomalies precursory to the nearby large and moderate earthquakes. The following conclusions can be drawn from this study.

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