Anomalous radon emission as precursor of earthquake

https://www.eri.u-tokyo.ac.jp/people/ichihara/vp2010plan/Manga_etal2009_MudVolcanoTriggering.pdf

Earthquake triggering of mud volcanoes

Many theoretical and empirical algorithms have been proposed in the literature for radon release; however whilst its relation with earthquake occurrence has been developed on occasions, there have been no specific complete studies of this phenomenon. In this study, radon monitoring was carried out using emanometry technique at Palampur and Dalhousie stations in the Kangra valley of Himachal Pradesh (India) from June 1996 to September 1999. Discrete radon concentrations were recorded in soil-gas and groundwater at both the stations. Radon anomalies were correlated with microseismic events recorded along the Main Boundary Thrust (MBT) of N-W Himalaya in the grid (30-34°N, 74-78°E). The influence of meteorological parameters viz, temperature, rainfall, relative humidity and wind velocity on radon concentration was qualitatively evaluated. The radon exhalation showed positive correlation with temperature, rainfall, relative humidity and negative correlation with wind velocity. Both positive and negative radon anomalies were recorded. The study reveals the precursory nature of radon anomalies and their correlation with microseismic events in 62% of the cases but prediction of earthquakes is yet a remote possibility. From the analysis it has been found that radon anomaly is not only influenced by seismic parameters but also by meteorological parameters and the nature of carrier gases/fluids. To learn more about the phenomenon, simultaneous recording of various gases (He, CO2, CH4) and meteorological parameters, together with multiple continuous measurements of radon have been suggested.

/pdf/earthquake-prediction-studies-using-radon-as-a-precursor-in-4wkqfh0zy2.pdf

Earthquake Prediction Studies Using Radon as a Precursor in N-W Himalayas, India: A Case Study

The soil-gas method is based on the principle that faults and/or fractures are highly permeable pathways in rock formation where gases can migrate upward from the deep crust and/or mantle and retain their deep-source signatures in the soil cover. This method is adopted because it can give results in short time and at low costs. In this work, soil-gas compositions are measured and synthesized in conjunction with the geological, geophysical and geomorphological information along the Chaochou Fault, which is considered as an active fault in southern Taiwan. More than 500 soil-gas samples were collected along 18 traverses crossing the observed structures and analyzed for He, CO 2 , CH 4 , O 2 + Ar and N 2 . The results show that both helium and carbon dioxide concentrations in the soil gas have anomalous values at the specific positions in each of the traverses. The trace of these positions coincides with the N-S trending faults and/or fractures, that is, the postulated trend and pattern of the faults in southern Taiwan. Hence, helium and carbon dioxide are useful index gases in this area. Based on the helium and carbon dioxide concentrations of the soil gases, at least three components are required to explain the observed variations. In addition to the atmospheric air component, two gas sources can be recognized. One is the deep crust component, exhibiting high He and CO 2 concentrations, and considered as best indicator for the surface location of fault/fracture zones in the region. The other component could be a shallower gas source with high CO2 concentration, and low He concentration. Moreover, helium isotopic compositions of representative samples vary from 0.52 to 1.05 Ra (the 3 He/ 4 He ratio of air), illustrating that most samples have soil air component and may be mixed with some crustal component but no significant input of mantle component. Carbon isotopic composition (δ 13 C) of carbon dioxide in the soil samples vary from ‐11.8 to ‐23.4‰, which could be the result of mixing of organic and limestone components. Both helium and carbon isotopic results support the multiple gas sources in studied area. Meanwhile, continuous monitoring indicates that soil gas variations at fault zone may be closely related to the local crustal stress and hence, is suitable for further monitoring on fault activities.

/pdf/reconnaissance-of-soil-gas-composition-over-the-buried-fault-4bvx5klv36.pdf

Reconnaissance of soil gas composition over the buried fault and fracture zone in southern Taiwan

Spatial variations of radon and helium concentrations in soil-gas across the Shan-Chiao fault, Northern Taiwan

Variations of soil radon and thoron concentrations in a fault zone and prospective earthquakes in SW Taiwan

Gas variations of many mud volcanoes and hot springs distributed along the tectonic sutures in southwestern Taiwan are considered to be sensitive to the earthquake activity. Therefore, a multi-parameter automatic gas station was built on the bank of one of the largest mud-pools at an active fault zone of southwestern Taiwan, for continuous monitoring of CO2, CH4, N2 and H2O, the major constituents of its bubbling gases. During the year round monitoring from October 2001 to October 2002, the gas composition, especially, CH4 and CO2, of the mud pool showed significant variations. Taking the CO2/CH4 ratio as the main indicator, anomalous variations can be recognized from a few days to a few weeks before earthquakes and correlated well with those with a local magnitude >4.0 and local intensities >2. It is concluded that the gas composition in the area is sensitive to the local crustal stress/strain and is worthy to conduct real-time monitoring for the seismo-geochemical precursors.

L. L. Chyi

Papers

Variations of soil radon and thoron concentrations in a fault zone and prospective earthquakes in SW Taiwan

Seismo-Geochemical Variations in SW Taiwan: Multi-Parameter Automatic Gas Monitoring Results