ORIGINAL PAPER Estimation of aseismic crustal-strain using radon precursors of the 2003 M 6.8, 2006 M 6.1, and 2008 M 5.0 earthquakes in eastern Taiwan T. Kuo Æ C. Lin Æ G. Chang Æ K. Fan Æ W. Cheng Æ C. Lewis Received: 30 October 2008 / Accepted: 7 July 2009 / Published online: 23 July 2009 Ó Springer Science+Business Media B.V. 2009 Abstract Aseismic crustal-strain signals prior to the 2003 Mw 6.8 Chengkung, 2006 Mw 6.1 Taitung, and 2008 Mw 5.0 Antung earthquakes with epicenters located 20, 55 and 11 km, respectively, from the Antung radon-monitoring station have been calculated using the radon anomalies recorded. Specifically, radon decreased from background levels of 791 ± 46, 762 ± 57, and 735 ± 48 pCi/L to minima of 326 ± 9, 371 ± 9, and 480 ± 43 pCi/L prior to the 2003, 2006, and 2008 earthquakes, respectively. The estimated aseismic crustal-strain maxima at the Antung hot spring during the rock dilation stage were 3.6, 2.7, and 1.3 ppm, respectively. The v-shaped radon pattern recognized in all three anomalies is valuable for detecting the aseismic strain precursory to disastrous earthquakes in the Antung hot spring which is situated in a brittle fractured aquifer of limited recharge surrounded by ductile mudstone. Keywords Radon anomaly  Aseismic crustal-strain  Groundwater  Earthquake List of symbols M Magnitude Mw Moment magnitude 1 Introduction Radon-222 is a chemically inert radioactive nuclide with a half-life of approximately 3.8 days. The radon concentration in groundwater is proportional to the uranium T. Kuo (&)  C. Lin  K. Fan  W. Cheng  C. Lewis Department of Mineral and Petroleum Engineering, National Cheng Kung University, Tainan, Taiwan e-mail: mctkuobe@mail.ncku.edu.tw G. Chang Central Weather Bureau, Taipei, Taiwan 123 Nat Hazards (2010) 53:219–228 DOI 10.1007/s11069-009-9423-y