3-D attenuation tomography from microseismicity in a mine

Abstract

SUMMARYWe perform 3-D attenuation tomography using microseismic data recorded during an underground mine development. The whole path attenuation parameter t* is obtained by least-squares inversion of P-wave amplitude spectra of the events recorded by 7 monitoring wells each containing 4 3C geophones. The corner frequencies obtained during P-wave spectral inversion of the 488 identified events range from 140 to 220 Hz which are typical for microseismic events with a negative moment magnitude of around –1. The quality factor Q obtained from tomographic inversion varies between 9 and 72 with the event cluster location characterized by a low Q value of 10. Two high Q regions of 30–72 are located at depths of 0.45 and 0.5 km, one between 0–0.15 km east and 0.3–0.5 km north which correlate with the high-grade ore deposit, and another centred around 0.45 km east and 0.25 km north. The high (-low) Q values, in general, correlates with the high (-low) velocities present in the velocity tomography model. A joint interpretation of seismic attenuation and velocity models reveals the heterogeneity present in the mine which aids in delineating the ore body using seismic waves in addition to other measurements such as gravity inversion and direct sampling from drillholes.