Developing and Exploiting a Unique Dataset from South African Gold Mines for Source Characterization and Wave Propagation

In this project, we have developed and exploited a unique seismic dataset to address the characteristics of small seismic events and the associated seismic signals observed at local ( 200 km) and regional ( 2000 km) distances. The dataset has been developed using mining-induced events from three deep gold mines in South Africa recorded on in-mine networks ( 1 km) composed of tens of high-frequency sensors, a network of four broadband stations installed as part of this project at the surface around the mines (1-10 km), and a network of existing broadband seismic stations at local/regional distances (50-1000 km) from the mines. The final dataset includes (i) 2 years (2007 and 2008) of continuous recording by the surface broadband array and (ii) tens of thousands of mine tremors in the -3.4 ML 4.4 local magnitude range recorded by high-frequency in-mine geophones. Events with positive magnitudes are generally well recorded by the surface-mine stations, while magnitudes of 3.0 and larger are seen at regional distances (up to 600 km) in high-pass filtered recordings. Significant effort has been devoted to quality control of the in-mine, high-frequency data gathered during this effort. The quality control consisted of (i) identification and analysis of outliers among the P- and S-wave travel-time picks reported by the in-mine network operator and (ii) verification of sensor orientations. The outliers have been identified through a Wadati filter developed during this project that searches for the largest subset of P- and S-wave travel-time picks consistent with a medium of uniform wave-speed. We have also detected that trigger times were mistakenly reported as origin times by the in-mine network operator, and corrections have been obtained from the intercept times in the Wadati diagrams. Sensor orientations have been verified by correlating empirically and theoretically rotated P-, SV-, and SH- waveforms. Published in Proceedings of the 2010 Monitoring Research Review - Ground-Based Nuclear Explosion Monitoring Technologies, 21-23 September 2010, Orlando, FL. Volume I. Sponsored by the Air Force Research Laboratory (AFRL) and the National Nuclear Security Administration (NNSA). U.S. Government or Federal Rights License