Comparison of ground motion from tremors and explosions in deep gold mines

Abstract

Seismic body waves, from tamped chemical explosions, two with yields of 50 and one of 150 kg, were compared with corresponding data from three mining‐induced tremors with a view to testing methods of discriminating between the two types of events. Detonated at depths of about 2 km, all three explosions generated P waves for which the low‐frequency spectral asymptotes agree well with corresponding results scaled down from nuclear shots at the Nevada Test Site. For the two smaller explosions, recorded underground at hypocentral distances ranging from 234 to 871 m, the P wave corner frequencies, defined by the intersections of the low‐ and high‐frequency asymptotes, are also in fine agreement with scaled‐down results from the Nevada Test Site; for the 150‐kg explosion, which was recorded only at the surface, it appears that 2.39 km of upward propagation caused the corner frequency to be at least a factor of 4 lower than anticipated due to attenuation. All three explosions generated S waves that appear to be a consequence of deviatoric stress release in the immediate environs of the explosions. The three tremors analyzed here generated P and S waves whose spectra and source parameters agree well with standard earthquake source models. With regard to discrimination based on P wave spectra, we conclude that for events of fixed low‐frequency spectral asymptotes, the explosions typically have higher corner frequencies than tremors or earthquakes, although counterexamples certainly exist. Interestingly, the 150‐kg explosion was identified as such on the basis of P and S wave polarities that are incompatible with the normally expected double‐couple source model; instead, these initial motions are consistent with an explosion in conjunction with normal faulting. The body wave spectra of this explosion and those of a nearby tremor, however, were indistinguishable.

Lithological Controls on Seismicity in Granitic Rocks

“…However, McGarr et al (1990) investigated the spectra of three explosions and three mining-induced earthquakes in an attempt to see differences between the two types, and found that the tremors and explosions both fit the commonly accepted f ‫2מ‬ decay. The main difference they find is that explosions typically have higher P-wave corner frequencies than tremors, for events of equal X 0P .…”

Source parameters and rupture velocity of smallM≤ 2.1 reservoir induced earthquakes

“…The earthquakes in this study have relatively high stress drop compared to both tectonic and induced earthquakes. Data points are: Cajon Pass (Abercrombie 1995), NE America (Boatwright 1994), Fenton Hill (Fehler & Phillips 1991), Loma Prieta (Hough et al 1991), URL (Gibowicz et al 1991), S. A Mines 1 (McGarr et al 1990), Mammoth Lakes (Archuleta et al 1982), Palm Springs (Mori & Frankel 1990), Large (compilation of Abercrombie & Rice 2005; table 5 of Dreger and Helmberger 1991; Mori 1996; Hough and Dreger 1995; Ji et al 2002; Venkataraman et al . 2000; Wald 1995; Wald & Heaton 1994; Wald et al .…”

“…The earthquakes in this study have relatively high stress drop compared to both tectonic and induced earthquakes. Data points are: Cajon Pass (Abercrombie 1995), NE America (Boatwright 1994), Fenton Hill (Fehler & Phillips 1991), Loma Prieta (Hough et al 1991), URL (Gibowicz et al 1991), S. A Mines 1 (McGarr et al 1990), Mammoth Lakes (Archuleta et al 1982), Palm Springs (Mori & Frankel 1990), Large (compilation of Abercrombie & Rice 2005; Dreger and Helmberger 1991;Mori 1996;Hough and Dreger 1995;Ji et al 2002;Venkataraman et al 2000;Wald 1995;Wald & Heaton 1994;Wald et al 1996;Wald et al 1991), S. A Mines 2 (Spottiswoode & McGarr 1975) and Long Valley (Ide et al 2003, individual and EGF studies). The shaded region shows the location of the results from Mandal et al (1998). It is difficult to measure rupture velocity of small earthquakes due to the attenuation of high frequency energy, and poor azimuthal coverage of recordings.…”

Moment Tensors and Other Source Parameters of Mining‐Induced Earthquakes in TauTona Mine, South Africa

“…In this study, we assume P-wave velocity α 5:9 km=s, S-wave velocity β 3:6 m=s, and density of ρ 2640 kg=m 3 , which is in the range of previous measurements surrounding the TauTona Mine. Cook (1963) measured α 5:94 5% km=s in the Witwatersrand sediments in the nearby ERPM Mine; and, similarly, McGarr et al (1990) found 5:85 ≤ α ≤ 6:05 km=s in the nearby Driefontein Gold Mine. More recently, measured the P-wave velocity on cores of damaged quartzite and cataclasite from the Pertorius fault zone and found values of 5:6 ≤ α ≤ 6:1 km=s.…”