Seismic Source Wave Propagation Analysis Using Laboratory AE Monitoring System

Abstract

ABSTRACT The source location algorithm in microseismic monitoring systems assumes a constant velocity model, which does not account for the effects of voids, fractures, backfills, and changing mine geometry in underground mines. This study investigated Acoustic Emission (AE) signal propagation characteristics towards signal receivers in laboratory physical models to understand the influence of various factors on seismic wave velocity. It was observed that the AE wave bypasses the voids and reflects off the backfill boundaries and follows the path of least resistance described by Fermat's principle and Snell's law. AE measurements show 1) similar signal travel time to sensors located across the void when the void in the concrete blocks was empty and when filled with various backfill types; 2) increasing backfill age had no influence on the signal travel time to the sensors. It was also found that the signal triggering behavior of the sensors in the proximity of the block voids is governed by Snell's law. This study concludes that the combination of the sensor network ray tracing method with Snell's law would be a promising solution to accurately determine applicable input wave velocities in seismic monitoring systems. INTRODUCTION The accurate location of seismic event sources is of practical importance for identifying seismic and burst-prone areas in underground mining, particularly when the ground condition and mine geometry are continuously changing. The effective tool employed by rockburst suspected underground mines to mitigate rockburst hazards is the microseismic monitoring system. The velocity model (VM) assigned to the rockmass is a fundamental parameter in microseismic monitoring systems used to define the seismic source parameters and to locate the seismic event sources. Several researchers pointed out that high uncertainties in microseismic source location come from the VM (Husen and Hardebeck, 2010; Collins et al. 2014; Reyes-Montes et al, 2016). The microseismic systems in most mines rely on a single or layered VM that is constant for source location purposes. This velocity model assumes an isotropic and homogeneous medium with the same properties throughout the volume of interest.