Spatial radon anomalies on active faults in California |
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| Institution: | 1. Geological Institute of the Kola Science Center, Russian Academy of Sciences, ul. Fersmana 14, Apatity, Murmansk, Region, 184209, Russia;2. Schmidt Institute of Physics of the Earth, Russian Academy of Sciences, ul. Bol. Gruzinskaya 10, Moscow, 123242, Russia;3. Institute of Geography, Russian Academy of Sciences, Staromonetnyi per. 29, Moscow, 119017, Russia;4. Institute of Earthquake Prediction Theory and Mathematical Geophysics, Russian Academy of Sciences, ul. Profsoyuznaya 84/32, Moscow, 117997, Russia;5. Institute of Marine Geology and Geophysics, Far Eastern Branch of the Russian Academy of Sciences, ul. Nauki 1B, Yuzhno-Sakhalinsk, 693022, Russia;1. Institute of Human Genetics, Hannover Medical School, Carl-Neuberg-Str. 1, 30625 Hannover, Germany;2. Institute of Pathology, Hannover Medical School, Carl-Neuberg-Str. 1, 30625 Hannover, Germany;3. Institute of Molecular Medicine. Goethe University Frankfurt am Main, Theodor-Stern-Kai 7, 60596 Frankfurt am Main, Germany;4. Institute of Experimental Hematology, Hannover Medical School, Carl-Neuberg-Str. 1, 30625 Hannover, Germany |
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| Abstract: | Radon emanation has been observed to be anomalously high along active faults in many parts of the world. We tested this relationship by conducting and repeating soil-air radon surveys with a portable radon meter across several faults in California. The results confirm the existence of fault-associated radon anomalies, which show characteristic features that may be related to fault structures but vary in time due to other environmental changes, such as rainfall. Across two creeping faults in San Juan Bautista and Hollister, the radon anomalies showed prominent double peaks straddling the fault-gouge zone during dry summers, but the peak-to-background ratios diminished after significant rain fall during winter. Across a locked segment of the San Andreas fault near Olema, the anomaly has a single peak located several meters southwest of the slip zone associated with the 1906 San Francisco earthquake. Across two fault segments that ruptured during the magnitude 7.5 Landers earthquake in 1992, anomalously high radon concentration was found in the fractures three weeks after the earthquake. We attribute the fault-related anomalies to a slow vertical gas flow in or near the fault zones. Radon generated locally in subsurface soil has a concentration profile that increases three orders of magnitude from the surface to a depth of several meters; thus an upward flow that brings up deeper and radon-richer soil air to the detection level can cause a significantly higher concentration reading. This explanation is consistent with concentrations of carbon dioxide and oxygen, measured in soil-air samples collected during one of the surveys. |
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