oa Velocity Model Determination for Accurate Location of Mining- induced Seismic Events

Detennining thè location of mining-induced seismic events is strongly dependent on having an acctirate velocity model. However, such a model is seldom available. This paper describes thè determination of a velocity model for seismic event location, using thè seismic events themselves as sources whose location is to be determined along witli tlie parameters of tlie velocity model (a simultaneous inversion of event locations and velocity struchire). Seismic monitoring of a mine in Colorado is used as an example, witli an array of geophones mstalled both on thè surface and in tuidergrotuid roadways. Velocity models of increasing complexity are considered, starting with a homogeneous velocity, movmg to a (slightly dipping) layered-earth model, and eventually hicludmg static time sliifts to accotuit for tlie effects of a weathered, near-surface, low- velocity layer on arrivai times at geophones motuited on tlie surface. This series of increasingly complex models obviously shows increasingly better fits to thè data, but also shows more plausible event locations, and with more realistic elevatimi spans. Examination of spadai patterns hi tlie residuals indicates tliat tliere are likely mining- induced changes in velocity tliat are not accotuited for hi tlie model.