Extension of Gutenberg-Richter distribution to MW-1.3, no lower limit in sight

With twelve years of seismic data from TauTona Gold Mine, South Africa, we show that mining-induced earthquakes follow the Gutenberg-Richter relation with no scale break down to the completeness level of the catalog, at moment magnitude M-W -1.3. Events recorded during relatively quiet hours in 2006 indicate that catalog detection limitations, not earthquake source physics, controlled the previously reported minimum magnitude in this mine. Within the Natural Earthquake Laboratory in South African Mines (NELSAM) experiment's dense seismic array, earthquakes that exhibit shear failure at magnitudes as small as M-W -3.9 are observed, but we find no evidence that M-W -3.9 represents the minimum magnitude. In contrast to previous work, our results imply small nucleation zones and that earthquake processes in the mine can readily be scaled to those in either laboratory experiments or natural faults. Citation: Boettcher, M. S., A. McGarr, and M. Johnston (2009), Extension of Gutenberg-Richter distribution to M-W -1.3, no lower limit in sight, Geophys. Res. Lett., 36, L10307, doi: 10.1029/2009GL038080.