Collaborative Research: Comprehensive Analysis of Seismic Processes in a Deep South African Mine

University Of Southern California, Los Angeles CA

Investigators

Abstract

Many fundamental questions in earthquake physics remain unresolved, largely because of difficulties in obtaining high-quality, near-source recordings of small earthquakes and deriving reliable source parameters. The overarching goal of this project is to provide an improved understanding of earthquake source processes for a wide magnitude range (approximately -4 to 4). We are performing detailed seismological investigations of source properties that characterize several distinct classes of seismic events (earthquakes, rockbursts, and blasts) in a 3.6 km deep South African mine. We will also conduct a short field campaign to record seismic events at the extremes of the magnitude range and in close proximity to fault structures. Full source tensor inversions, second moment analysis, and spectral methods will be used to determine comprehensive sets of source properties including scalar potencies/moments, focal mechanisms, corner frequencies, strain/stress drops, radiated energies, rupture velocities, and source time functions. Special effort will be devoted to detecting isotropic components of faulting. Theoretical calculations of expected radiation from different event types will help in the interpretation of results. Applying the above analysis to the small-magnitude, near source seismic data will allow us to obtain constraints on many aspects of earthquake physics including nucleation processes, the prevalence of isotropic components of seismic radiation, changes in the physics of rupture with event magnitude or with proximity to geologic and mining structures, and source parameter differences between earthquakes, explosions, and other seismic sources. The high-resolution results on seismic source properties and scaling relations will significantly impact the earthquake physics and rock mechanics communities by helping to resolve long-term controversies on earthquake nucleation and rupture processes, scaling of laboratory results to natural faults, and earthquake energy budgets, among others. In addition, the findings on spatially dependent seismic properties will be useful for decision-making concerning when and where to suspend mining activities to enhance underground safety