Antung Hot Spring Research Articles

Precursory Behavior of Groundwater Radon in Southeastern Taiwan: Effect of Tectonic Setting in the Subduction Zone

Monitoring precursory decline in groundwater radon at the Antung hot spring is a useful means of forecasting the magnitude and precursor time of local disastrous earthquakes. With the help of a case study in southeastern Taiwan, this paper demonstrates the effect of tectonic setting in the subduction zone on the correlation between radon decline, precursory time and earthquake magnitude. Given a radon-monitoring site located near the plate boundary in the tectonic setting of advanced arc-continental collision, the observed radon decline and precursory time prior to the earthquakes in the tectonic setting of initial arc-continental collision are smaller than those observed prior to the earthquakes occurring on the plate boundary in the tectonic setting of advanced arc-continental collision. In the advanced arc-continental collision state, the coupling between the plates is strong and the stress transfer is efficient, whereas in the incipient collision state, the coupling and stress transfer are not as good. It also takes additional time lag and attenuation for the stress transfer from one tectonic setting to the other. This paper presents the difference in the precursory behavior of groundwater radon between earthquakes which occurred in two different tectonic settings: advanced and initial arc-continental collision.

F79GENOME-WIDE ASSOCIATION STUDY OF CIRCADIAN RHYTHMICITY IN 71,500 UK BIOBANK PARTICIPANTS AND POLYGENIC ASSOCIATION WITH MOOD INSTABILITY

Radon volatilization mechanism into the gas phase was hypothesized to explain the anomalous declines in groundwater radon precursory to three major earthquakes – (1) 2003 MW = 6.8 Chengkung, (2) 2006 MW = 6.1 Taitung, and (3) 2008 MW = 5.4 Antung in Taiwan. The epicenters were located 24 km, 52 km, and 13 km from the Antung radon-monitoring well D1, respectively. To verify the mechanism of in situ volatilization, we monitored groundwater-dissolved ethane in addition to radon and methane at well D1 in the Antung hot spring since November 30, 2010. The mechanism of in situ radon volatilization has been corroborated by the simultaneous concentration declines in groundwater-dissolved radon, methane, and ethane precursory to the 2011 MW 5.0 Chimei earthquake. The epicenter was located 32 km from the Antung radon-monitoring well D1. Observations at the Antung hot spring also suggest that radon is the best-choice tracer among the groundwater-dissolved gases for strain changes in the crust preceding an earthquake. On the southern segment of the Chihshang fault, the observed radon minima decrease as the earthquake magnitude increases.

A Stress Condition in Aquifer Rock for Detecting Anomalous Radon Decline Precursory to an Earthquake

Recurrent groundwater radon anomalous declines were observed from well measurements in the Antung hot spring area (eastern Taiwan) prior to five of six earthquakes that occurred between 2003 and 2011 (M w range 5.0–6.8). The relationship between the detectability of radon anomalies and the first motions of P-waves was investigated. Based on the first motions of P-waves recorded near the investigated well, a precursory decrease in groundwater radon can be detected only when the first motion is compression. No precursory change in groundwater radon concentration was observed for the downward first motion of P-waves.

Concurrent concentration declines in groundwater-dissolved radon, methane and ethane precursory to 2011 MW 5.0 Chimei earthquake

Radon volatilization mechanism into the gas phase was hypothesized to explain the anomalous declines in groundwater radon precursory to three major earthquakes – (1) 2003 MW = 6.8 Chengkung, (2) 2006 MW = 6.1 Taitung, and (3) 2008 MW = 5.4 Antung in Taiwan. The epicenters were located 24 km, 52 km, and 13 km from the Antung radon-monitoring well D1, respectively. To verify the mechanism of in situ volatilization, we monitored groundwater-dissolved ethane in addition to radon and methane at well D1 in the Antung hot spring since November 30, 2010. The mechanism of in situ radon volatilization has been corroborated by the simultaneous concentration declines in groundwater-dissolved radon, methane, and ethane precursory to the 2011 MW 5.0 Chimei earthquake. The epicenter was located 32 km from the Antung radon-monitoring well D1. Observations at the Antung hot spring also suggest that radon is the best-choice tracer among the groundwater-dissolved gases for strain changes in the crust preceding an earthquake. On the southern segment of the Chihshang fault, the observed radon minima decrease as the earthquake magnitude increases.

Correlating Precursory Declines in Groundwater Radon with Earthquake Magnitude

Both studies at the Antung hot spring in eastern Taiwan and at the Paihe spring in southern Taiwan confirm that groundwater radon can be a consistent tracer for strain changes in the crust preceding an earthquake when observed in a low-porosity fractured aquifer surrounded by a ductile formation. Recurrent anomalous declines in groundwater radon were observed at the Antung D1 monitoring well in eastern Taiwan prior to the five earthquakes of magnitude (Mw ): 6.8, 6.1, 5.9, 5.4, and 5.0 that occurred on December 10, 2003; April 1, 2006; April 15, 2006; February 17, 2008; and July 12, 2011, respectively. For earthquakes occurring on the longitudinal valley fault in eastern Taiwan, the observed radon minima decrease as the earthquake magnitude increases. The above correlation has been proven to be useful for early warning local large earthquakes. In southern Taiwan, radon anomalous declines prior to the 2010 Mw 6.3 Jiasian, 2012 Mw 5.9 Wutai, and 2012 ML 5.4 Kaohsiung earthquakes were also recorded at the Paihe spring. For earthquakes occurring on different faults in southern Taiwan, the correlation between the observed radon minima and the earthquake magnitude is not yet possible.

Correlating recurrent radon precursors with local earthquake magnitude and crust strain near the Chihshang fault of eastern Taiwan

The active Chihshang fault in the southern segment of longitudinal valley of eastern Taiwan is part of the suture boundary between the Eurasia plate and the Philippine Sea plate. Radon anomalies in groundwater were recorded prior to three major earthquakes—(1) 2003 Mw = 6.8 Chengkung, (2) 2006 Mw = 6.1 Taitung, and (3) 2008 Mw = 5.4 Antung. The epicenters were located 24, 52, and 13 km, respectively, from the radon-monitoring well (D1) in the Antung hot spring about 3 km southeast of the Chihshang fault. Prior to the three major earthquakes, radon decreased from background levels of 787 ± 42, 762 ± 57, and 700 ± 57 pCi/L to minima of 326 ± 9, 371 ± 9, and 480 ± 43 pCi/L, respectively. Based on the radon volatilization model and the rock dilatancy model, this paper correlates the observed radon minima with local earthquake magnitude and crust strain. The correlation is a useful means of forecasting local disastrous earthquakes in the southern segment of longitudinal valley of eastern Taiwan.

Simultaneous declines in radon and methane precursory to 2008 M W 5.0 Antung earthquake: corroboration of in-situ volatilization

Radon volatilization mechanism into the gas phase was hypothesized to explain the anomalous decline in groundwater radon precursory to the 2003 M W = 6.8 Chengkung earthquake in Taiwan. We initiated the monitoring of both radon and methane in the groundwater since November 2007 at well D1 in the Antung hot spring. The mechanism of in-situ radon volatilization has been corroborated by the simultaneous anomalous declines in groundwater-dissolved radon and methane precursory to the 2008 M W 5.0 Antung earthquake.

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

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.

Investigation of precursory phenomena in the ionosphere, atmosphere and groundwater before large earthquakes of M > 6.5

Investigation of precursory phenomena in the ionosphere, atmosphere and groundwater before large earthquakes of M > 6.5

A Mechanism for Anomalous Decline in Radon Precursory to an Earthquake

Mechanisms for interpreting anomalous decreases in radon in ground water prior to earthquakes are examined with the help of a case study to show that radon potentially is a sensitive tracer of strain changes in the crust preceding an earthquake. The 2003 Chengkung earthquake of magnitude (M) 6.8 on December 10, 2003, was the strongest earthquake near the Chengkung area in eastern Taiwan since 1951. The Antung radon-monitoring station was located 20 km from the epicenter. Approximately 65 d prior to the 2003 Chengkung earthquake, precursory changes in radon concentration in ground water were observed. Specifically, radon decreased from a background level of 780 pCi/L to a minimum of 330 pCi/L. The Antung hot spring is situated in a fractured block of tuffaceous sandstone surrounded by ductile mudstone. Given these geological conditions, we hypothesized that the dilation of brittle rock mass occurred at a rate faster than the recharge of pore water and gas saturation developed in newly created cracks preceding the earthquake. Radon partitioning into the gas phase may explain the anomalous decrease of radon precursory to the 2003 Chengkung earthquake. To support the hypothesis, vapor-liquid, two-phase radon-partitioning experiments were conducted at formation temperature (60 degrees C) using formation brine from the Antung hot spring. Experimental data indicated that the decrease in radon required a gas saturation of 10% developed in rock cracks. The observed decline in radon can be correlated with the increase in gas saturation and then with the volumetric strain change for a given fracture porosity.

Anomalous decrease in groundwater radon before the Taiwan M6.8 Chengkung earthquake

On December 10, 2003, an earthquake of magnitude (M) 6.8, the strongest since 1951, occurred near the Chengkung area in eastern Taiwan. Approximately 65 d prior to the 2003 Chengkung earthquake, precursory changes in the groundwater radon concentration were observed at the Antung radon-monitoring station located 20 km from the epicenter. The radon anomaly was a decrease from a background level of 28.9 Bq L −1 to a minimum of 12.2 Bq L −1. Observations at the Antung hot spring suggest that the groundwater radon, when observed under suitable geological conditions, can be a sensitive tracer for strain changes in the crust preceding an earthquake.