INFLUENCE OF SOURCE REGION PROPERTIES ON SCALING RELATIONS FOR M-LESS-THAN-0 EVENTS

Excavation induced seismic events with moment magnitudes M < 0 are exa mined in an attempt to determine the role geology, excavation geometry , and stress have on scaling relations. Correlations are established b ased on accurate measurements of excavation geometry and methodology, stress regime, rock mass structure, local tectonics, and seismic locat ions. Scaling relations incorporated seismic moments and source radii obtained by spectral analysis, accounting for source, propagation, and site effects, and using Madariaga's dynamic circular fault model. Obs ervations suggest that the interaction of stresses with pre-existing f ractures, fracture complexity and depth of events are the main factors influencing source characteristics and scaling behaviour. Self-simila r relationships were found for events at similar depths or for weakly structured rock masses with reduced clamping stresses, whereas a non-s imilar behaviour was found for events with increasing depth or for hea vily fractured zones under stress confinement. Additionally, the scali ng behaviour for combined data sets tended to mask the non-similar tre nds. Overall, depth and fracture complexity, initially thought as seco nd order effects, appear to significantly influence source characteris tics of seismic events with M < 0 and consequently favour a non-simila r earthquake generation process.