Quasi-static slip patch growth to 20 m on a geological fault inferred from acoustic emissions in a South African gold mine

摘要: Three months of acoustic emission (AE) monitoring in a South African gold mine down to Mw −5 revealed newly emergent planar cluster 7557 events −3.9 ≤ Mw ≤ −1.8 (typical rupture radius 6–70 cm) that expanded with time reach size 20 m on preexisting geological fault near an active mining front 1 km beneath the ground. It had sharply defined, configuration, hypocenters aggregated within thickness only several decimeters. We infer zone defines aseismic slip patch fault, wherein individual AEs represent failures very small asperities being loaded by slip. Additional support for interpretation was obtained analyzing composite focal mechanisms and repeating events. The expansion over 2 months likely quasistatic because all ruptured much smaller areas than at corresponding time. b values dropped gradually from 2.6 1.4, consistent significant increase shear stress expected style. Another similar characteristics emerged later neighboring part same grew 10 m extent last weeks study period. quasi-static inferred localized slow-slip patches sizes 10–20 m suggests critical crack length natural faults can be least as large, exceeding decimeter range derived laboratory stick-slip experiments saw-cut rocks.