L. Q. Ge et al.
anomaly may be caused by a alternant deformation to expa nd the porosity or the radon releases from the rock
fit fully.
4. The Discussion about ERA in Time -Space Domain
As t he hal f -life of 222Rn is only 3.825 days , t he diffusion le ngth of radon in water is jus t a few centimeters. For
this reason, the range of a radon anomaly in underground water is strongly depended on the moveme nt of under
groundwat e r . Si nc e the r adio ac tive deca y equilibriu m between 222Rn a nd226Ra in a closed water-rock syste m
takes 38 days tha t is about 10 times half-time of 222Rn, the range of ERA should co ver the dis tance of under-
ground water movement in 38 days.
The time span of ERA is the whole time of rock stres s acc umulating. To the s hort-t ime “slope type ” pattern
caused by single co mpre ssion change, it takes 38 days to balance the radium-radon decay. For the long time ten-
sile stres s accumulating, the “slope style” anomaly devel ops in multistep. It will impa ct t he whole process of
sustained compression. The descent st a ge of “hook style” anomaly may de cline in multistep; the ascent sta ge
presents rock broken superimposed many times. The “puls e s tyle” anomaly caused by radon released fitfully
takes very short time to be formed. According to the monitor ing da ta to free radon released from soil, the puls e
style is measured in units of hours or days. While it caused by a rock alternant deformation, the anomaly will
sustain for longer time. In add ition, the more “pulse style” anomalies appear t he more tremendously stress
chan ge will happen near the monitoring statio n.
5. Conclusion
In the pro cess of seismogenic, no matter rocks e nd ure compr e ssio n, stretc hin g, or deformation, t he free radon
concentration in rock pores will change a nd an E a r t hqua ke Radon Ano ma ly (ERA) will form in sei smogenic
zone . The morphology of ERA can be described as “slope-type”, “hook-type” and “pul s e-type”. The slope type
represents the undergro und radon anomaly in the se ismogenic s tretch area. T he ERA can cover where the un-
der ground water with radon moves in 38 days a nd go thr ough the whole time of ro ck sustained c ompressi on.
The ERA can reflect the states the rock in suc h as stretch, compression and br oken. So the monitorin g statio n
should be located not only te nsile area but al so compre ssive zone. By analyzing the re giona l ERA comprehen-
sively, we provide important reference information for seis molo gy a nd e arthqua ke p red ictio n.
Acknowledgements
The autho rs grat e f ul ly acknowle dge the financi a l support of: (1) National Natural Science Founda ti on of China
thro ugh Gra nt No. 41074093 entitled “Research on mechanism of earthquake radon anomal y”. (2) The Na tional
High-tech Re search and De velopme nt Program of China t hrough Grant 2012AA061803 entitled “Develop ment
of high precisio n nuclear rad iatio n spectrometry”.
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