Source parameters of acoustic emission events and scaling with mining‐induced seismicity

Abstract

[1] A series of uniaxial compression tests were performed on 96-mm-diameter quartzite samples, 242 mm in length, to understand the scaling of rock fracture processes. Nine acoustic emission (AE) sensors glued to each sample monitored the AEs resulting from microcracking within the samples. In contrast to previous AE studies, the sensors were calibrated as velocity transducers so that the output could be compared to mining-induced seismicity and natural earthquakes. A new hybrid, relative moment tensor method was applied to obtain source mechanism solutions for eight clusters of events. Once the AE rate accelerated prior to failure, the event positions are associated with the observed failure planes. The moment tensors were found to have double-couple components, indicating that shearing was occurring. The stress drop appears to be constant over the range of moments suggesting the self-similar scaling of the fracture response from the laboratory sample to mine seismicity and natural earthquakes over a wide range of length scales. Similar conclusions can be drawn by considering the apparent stress and source radius. The scaling of the peak velocity and peak acceleration parameters is apparently consistent with mining-induced seismicity but is considerably affected by high-frequency attenuation and the limited bandwidth. This is confirmed by the frequency-magnitude plot, which has a slope of unity. The fracture processes in the laboratory are similar to those occurring underground near stope faces and pillars in deep-level South African gold mines, where there is a high vertical compression and low confinement.

Preslip and cascade processes initiating laboratory stick slip

“…This is consistent with previous work which showed that the largest AEs had predominantly deviatoric focal mechanisms [Sellers et al, 2003;Thompson et al, 2005Thompson et al, , 2009.…”

Evolution of source characteristics of AE events during frictional sliding

“…The estimated magnitudes of stress drop were in the same range as those of the AE events associated with fracture of intact rocks (Sellers et al, 2003) and natural earthquakes. The average σ of the small-and the large-sliding events was 6.2±3.2 and 3.1±1.9 MPa, respectively.…”

“…Acoustic emission (AE) events have been observed during frictional sliding on pre-cut faults in laboratory rock samples (e.g., Weeks et al, 1978;Sammonds and Ohnaka, 1998;Yabe et al, 2003). The AE sources were located on the pre-cut fault, and their focal mechanism solution was consistent with that expected theoretically for macroscopic sliding.…”

Observation of numerous aftershocks of an Mw 1.9 earthquake with an AE network installed in a deep gold mine in South Africa

“…If we assume a unity b-value for the GutenbergRichter's relationship, which was also confirmed down to M 0 by the ISS catalog, the fact that our network detected ∼3000 times more events means that we probably detected many events as small as M −3.5 to approximately −4.5. If a 3-MPa stress drop is assumed (Sellers et al, 2003), the source dimension of an M ∼ −4 earthquake is about 0.1 m, which comes into the range of typical laboratory samples. Such a dimension is also consistent with the shortest range of pulse width observed for many events.…”