In southwestern Taiwan, radon anomalous declines prior to the 2010 Mw 6.3 Jiasian and 2016 Mw 6.4 Meinong earthquakes were recorded at the Paihe spring. The above-mentioned earthquakes are the two strongest since 1964 that have occurred near the area southeast of Chiayi. The Paihe spring (P1) is located 46 km and 45 km, respectively, from the epicenters of the 2010 Mw 6.3 Jiasian and 2016 Mw 6.4 Meinong earthquakes. Specifically, the concentration of groundwater radon decreased from background levels of 144 ± 7 and 137 ± 8 pCi/L to minima of 104 ± 8 and 97 ± 9 pCi/L prior to the 2010 Mw 6.3 Jiasian and 2016 Mw 6.4 Meinong earthquakes, respectively. The Paihe spring is from an unconfined limestone aquifer surrounded by ductile shale and sandy shale. The v-shaped pattern of radon behavior in the Paihe spring is quite similar to those radon decreases that were measured in the confined andesite aquifer at Antung in eastern Taiwan. Recurrent anomalous declines in the concentration of groundwater radon were observed at well D1 in the Antung hot spring in eastern Taiwan prior to the five major earthquakes –2003 Mw 6.8 Chengkung, 2006 Mw 6.1 and Mw 5.9 Taitung, 2008 Mw 5.4 Antung, and 2011 Mw 5.0 Chimei. Well D1 is located 24 km, 52 km, 47 km, 13 km, and 32 km, respectively, from the epicenters of the 2003 Mw 6.8, 2006 Mw 6.1 and Mw 5.9, 2008 Mw 5.4, and 2011 Mw 5.0 earthquakes. The 2003 Mw 6.8 Chengkung was the strongest earthquake near the Chengkung area in eastern Taiwan since 1951. Specifically, radon decreased from a background level of 787 ± 42 pCi/L to a minimum of 326 ± 9 pCi/L prior to the 2003 Mw 6.8 Chengkung earthquake. In a brittle aquifer under undrained conditions (Antung and Paihe), 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 groundwater radon prior to the 2003 Chengkung earthquake. Both observations at Paihe and Antung suggest that in-situ radon volatilization offers an attractive mechanism for a premonitory decrease in groundwater radon. “A low-porosity brittle aquifer with un-drained conditions” is a suitable geological site to consistently detect precursory declines in groundwater radon prior to local large earthquakes. A longterm monitoring of precursory declines in groundwater radon at a suitable geological site can be a useful means for forecasting local disastrous earthquakes. At a suitable geological site, it is of a great practical value to develop the correlations among the scale of radon decline, precursory time, and earthquake magnitude for a given seismogenic fault.
|主出版物子標題||Monitoring Technology, Disaster Management and Impact Assessment|
|發行者||Nova Science Publishers, Inc.|
|出版狀態||Published - 2017 一月 1|
All Science Journal Classification (ASJC) codes
- 環境科學 (全部)