Increased radon-222 in soil gas because of cumulative seismicity at active faults

Abstract

This study demonstrates how the radon-222 ( 222 Rn) concentration of soil gas at an active fault is sensitive to cumulative recent seismicity by examining seven active faults in western Japan. The 222 Rn concentration was found to correlate well with the total earthquake energy within a 100-km radius of each fault. This phenomenon can probably be ascribed to the increase of pore pressure around the source depth of 222 Rn in shallow soil caused by frequently induced strain. This increase in pore pressure can enhance the ascent velocity of 222 Rn carrier gas as governed by Darcy's law. Anomalous 222Rn concentrations are likely to originate from high gas velocities, rather than increased accumulations of parent nuclides. The high velocities also can yield unusual young gas under the radioactive nonequilibrium condition of short elapsed time since 222 Rn generation. The results suggest that ongoing seismicity in the vicinity of an active fault can cause accumulation of strain in shallow fault soils. Therefore, the 222 Rn concentration is a possible gauge for the degree of strain accumulation.

Radon emission from soil gases in the active fault zones in the Capital of China and its environmental effects

“…As a natural and radioactive gas, the sudden and catastrophic, or quiet and continuous release of radon into the near-surface environment can result in health risks to the inhabitants living in adjacent areas 3 , 6 , 51 .…”

“…Higher soil radon concentrations and fluxes have been widely observed in fault zones 8 , 11 , 14 , due to (1) fault displacement during the late Quaternary Era, and (2) recent earthquakes in nearby faults 15 , 51 . In this study, non-negligible radon exhalations from active fault zones in the seismic zones near Beijing were observed (Tables 1 and 2 ), with soil radon concentrations of 7.65 to 64.14 kBq m −3 , comparable to the concentrations of radon in other fault zones (0.40 to 76.00 kBq m −3 ), seismic ruptures produced by strong earthquakes (0.04 to 106.64 kBq m −3 ), sandstone-type uranium deposits (2.23 to 84.74 kBq m −3 ), and forests where nuclides were released accidentally from the Fukushima Daiichi Nuclear Power Plant in March 2011 (7.50 to 23.00 kBq m −3 ).…”

Seismicity controlled by resistivity structure: the 2016 Kumamoto earthquakes, Kyushu Island, Japan

“…Zone A corresponds to the southern part of Hinagu fault, which is 10-50 km from the hypocenter of the main shock. Zone A includes a zone of high radon-222 concentration in soil gas, which suggests large gas ascent velocities caused by frequently induced strain along the Hinagu fault (Koike et al 2014). Further, a conductive zone like Seis.…”

Radon applications in geosciences – Progress & perspectives

“…[15][16][17][18][19][20][21][22][23]). The main rationale is an expected enhancement in radon exhalation due to stress associated with the preparatory stages of an earthquake.…”