Evaluation of tectonically enhanced radon in fault zones by quantification of the radon activity index

Abstract

This work highlights the importance of the Geogenic Radon Potential (GRP) component originated by degassing processes in fault zones. This Tectonically Enhanced Radon (TER) can increase radon concentration in soil gas and the inflow of radon in the buildings (Indoor Radon Concentrations, IRC). Although tectonically related radon enhancement is known in areas characterised by active faults, few studies have investigated radon migration processes in non-active fault zones. The Pusteria Valley (Bolzano, north-eastern Italy) represents an ideal geological setting to study the role of a non-seismic fault system in enhancing the geogenic radon. Here, most of the municipalities are characterised by high IRC. We performed soil gas surveys in three of these municipalities located along a wide section of the non-seismic Pusteria fault system characterised by a dense network of faults and fractures. Results highlight the presence of high Rn concentrations (up to 800 kBq·m−3) with anisotropic spatial patterns oriented along the main strike of the fault system. We calculated a Radon Activity Index (RAI) along north–south profiles across the Pusteria fault system and found that TER is linked to high fault geochemical activities. This evidence confirms that TER constitutes a significant component of GRP also along non-seismic faults.

A Case Study of the Radon Hazard at the Boundary of a Coal Minefield

“…These findings have been attributed to certain hypotheses. As previously mentioned, tectonic disturbances lead to zones of rock crushing, which allows for radon emanation [33,34]. The primary factors responsible for the manifestation of gas anomalies of this nature have been recognized as fault dynamics (i.e., fault activity) and types (i.e., dynamic types, such as thrusting, faulting, and fault rupture, among others), as well as other factors [35][36][37].…”

Natural Sinkhole Monitoring and Characterization: The Case of Latera Sinkhole (Latium, Central Italy)

“…The HVSR method relies on the analysis of the spectral ratio between the horizontal (H) and the vertical (V) components of ground motion originated by ambient vibrations and recorded using a three-component (accelerometers or velocimeters) single station. According to many authors, the frequency corresponding to the maximum value of the HVSR function was shown to have a strict correspondence with the local resonance frequency f0 of a site (see, among many others, [61][62][63][64][65]). The HVSR curve may exhibit several peaks, caused by the presence at depth of sedimentary layers contrasting in lithology and, thus, also in acoustic impedance (i.e., the product of geologic material density and its seismic velocity).…”

Radon Hazard of the Zhurinsky Fault for the Population in the Kuznetsk Coal Basin: Primary Results

“…Also, the type of crushing zone could influence the formation of such a large area with high values. Radon from a disturbance can be localized along the line of the displacement or it may not be detected in the displacement at all, and other options are also possible [48]. However, according to Swedish criteria [49], values above 10,000 require conventional measures to reduce the entry of radon into residential premises.…”