The release pattern we observed is consistent with our previous work with artificially doped shale gas reservoir rocks [Bauer et al., 2016] and past experiments recording radon exhalation rates from rocks undergoing deformation [Holub and Brady, 1981; Tuccimei et al., 2010; Mollo et al., 2011]; however, by using helium and argon as opposed to 222Rn, we achieve significantly better temporal resolution as we are not limited by decay counting rates for detection. These gases appearto be released in discrete cracking events, which is consistent with field scale observations of 222Rn bursts in tunnel air [Trique et al., 1999].