Tidal stress/strain and acoustic emission activity at the Underground Research Laboratory, Canada

Abstract

[1] We study the correlation between the phase of the moon and the occurrences of acoustic emissions (AEs) monitored at the Underground Research Laboratory in Canada. On 9 December 1997, a significant increase of AEs began and this activity decayed with time day by day. During the period of the decay, we observed that the activity often increased. Most of these increases corresponded with moments of new or full moon. We investigate whether the increase of AEs is correlated with the moments of new or full moon using a statistical method. We consider two models concerned with the daily occurrence rate of AEs. In the first model, the existence of the correlation is not assumed. In the second model, the existence is assumed. Using AIC (Akaike Information Criterion), it is shown that the second model is a significantly better fit to the observed time series of AEs.

Tidal Stress/Strain and the b-values of Acoustic Emissions at the Underground Research Laboratory, Canada

“…This is because, in the case of the laboratory experiments mentioned above, changes in b-values are observed for stress changes between a few tens and a few hundreds of MPa. However, it should also be noted that there is a correlation between the activity of AEs and small stress fluctuations related to the phase of the moon (IWATA, 2002). This implies that the occurrence of AEs at the URL is very sensitive to small stress changes.…”

“…2). However, during this decay period AE activity sometimes briefly increased, and these increases were found to correlate with the phase of the moon (IWATA, 2002). In this study, we used AEs that occurred between 23:00 on 9 December, 1997 and 24:00 on 27 March, 1998 (the same events as those used in IWATA, 2002).…”

“…IWATA (2002) investigated the time series of AEs monitored at the Underground Research Laboratory (URL) ( Fig. 1(a)) in Canada, and found a significant correlation between the occurrence of AEs and the phase of the moon.…”

“…1(a)) in Canada, and found a significant correlation between the occurrence of AEs and the phase of the moon. In this study, we examined the same data set as used in IWATA (2002) to investigate the correlation between the b-value of AEs at the URL and tidal stress/strain fluctuations. Because IWATA's (2002) results imply that the activity of the AEs is sensitive to tidal stress/strain fluctuations, we expected that the b-value of the AEs would also be sensitive to this effect.…”

“…The frequency number of AEs monitored at the URL, as a function of M u , between 23:00 on 9 December, 1997 and 24:00 on 27 March (the same period as for the data used inIWATA, 2002). The black and gray circles denote the two combinations of the upper and lower thresholds of M u used in this study.…”