Preseismic atmospheric radon anomaly associated with 2018 Northern Osaka earthquake

Abstract

Despite the challenges in identifying earthquake precursors in intraplate (inland) earthquakes, various hydrological and geochemical measurements have been conducted to establish a possible link to seismic activities. Anomalous increases in radon (222Rn) concentration in soil, groundwater, and atmosphere have been reported prior to large earthquakes. Although the radon concentration in the atmosphere is lower than that in groundwater and soils, a recent statistical analysis has suggested that the average atmospheric concentration over a relatively wide area reflects crustal deformation. However, no study has sought to determine the underlying physico-chemical relationships between crustal deformation and anomalous atmospheric radon concentrations. Here, we show a significant decrease in the atmospheric radon concentration temporally linked to the seismic quiescence before the 2018 Northern Osaka earthquake occurring at a hidden fault with complex rupture dynamics. During seismic quiescence, deep-seated sedimentary layers in Osaka Basin, which might be the main sources of radon, become less damaged and fractured. The reduction in damage leads to a decrease in radon exhalation to the atmosphere near the fault, causing the preseismic radon decrease in the atmosphere. Herein, we highlight the necessity of continuous monitoring of the atmospheric radon concentration, combined with statistical anomaly detection method, to evaluate future seismic risks.

Estimation of 238U and 232Th in soil and water of prominent fault region of Mizoram

“…Authors like Omori et al [47], Schekotov et al [48] and Mohammad et al [49] fails to correlate radon anomaly with parameters like tidal loading and atmospheric electromagnetic radiation before earthquakes. Quiescence in radon concentration was also observed by Muto et al [50] before the 2018 Osaka earthquake. A positive correlation between radon anomaly and earthquakes was also recently reported by some authors [51][52][53], where analytical methods like chaos method, decomposition methods, machine intelligence and stacking methods were successfully used to identify the radon anomaly.…”

“…This observation ignites opti-mism among researchers to predict earthquakes by monitoring radon anomaly and soon it becomes a global phenomenon that continues till dates [5-11, 37-39, 47-53]. Uncertainty and inaccuracy in prediction remained the main issue of present-day researchers, which is very well visible from some recent reports [37][38][39][47][48][49][50][51][52][53]. Chowdhury et al [38] and Sahoo et al [39] from the east and north India, respectively observed unpredicted earthquakes and false radon anomaly peaks, though they observed a positive correlation between them.…”

SafeNet: SwArm for Earthquake Perturbations Identification Using Deep Learning Networks

“…Moreover, continuous monitoring of soil gas radon and water radon concentrations along with the Amritsar (Punjab, India) seismic zone correlation showed that the amplitude of radon gas anomalies was positively correlated with earthquake magnitude [57]. In addition, recent studies revealed a significant decrease in radon concentration within continuous measurements of radon concentration in the atmosphere before the 2018 earthquake in northern Osaka, Japan [58] and peculiar changes in radon concentration in the atmosphere two months before the 1995 Kobe earthquake in Japan [59]; Fu et al [60] studied the radon gas anomalies in northern and northeastern Taiwan before the earthquake and observed a significant increase in soil radon concentration from a few days to a few weeks before the earthquake. Finally, it is reasonable that the amount of emitted radon could depend on the rupture length of the fault, that is, the magnitude of the seismic event.…”

Relationships among Indoor Radon, Earthquake Magnitude Data and Lung Cancer Risks in a Residential Building of an Apulian Town (Southern Italy)

“…The 2012 Pollino (Calabria, Italy) seismic sequence, culminating in a moment magnitude (Mw) 5.2 earthquake on 25 October 2012, was investigated by exploiting data collected during a long-term continuous radon monitoring experiment performed in the epicentral area from late 2011 to the end of 2014, this work has identified characteristic variations in radon exhalations during the preparation processes of large earthquakes [57]. The necessity of continuous monitoring of atmospheric radon concentrations combined with statistical anomaly detection methods to evaluate future seismic risks [45,52,[58][59][60], as well as low-cost radon monitoring methods and the application of expert systems to the prevention of indoor radon gas exposition risks, have been reported [61][62][63][64].…”

“…During this seismic quiescence, deep-seated sedimentary layers in the Osaka Basin, which might have been the main sources of radon, became less damaged and fractured. The reduction in damage led to a decrease in radon exhalation to the atmosphere near the fault, causing the pre-seismic radon decrease observed in the atmosphere [60].…”