Developing and Exploiting a Unique Seismic Data Set from South African Gold Mines for Source Characterization and Wave Propagation

In this project, we are developing and exploiting a unique seismic data set to address the characteristics of small seismic events and the associated seismic signals observed at local (< 200 km) and regional (< 2000 km) distances. The data set is being developed using mining-induced events from 3 deep gold mines in South Africa recorded on in-mine networks (< 1 km) comprised of hundreds of high-frequency sensors, a network of broadband seismic stations installed as part of this project at the surface around the mines (1 - 50 km), and a network of existing broadband seismic stations at local and regional distances (50 - 1000 km) from the mines. The final data set will contain: (1) events spanning 5 orders of magnitude (M from approximately -1 to 3) well recorded at a wide range of local and regional distances, (2) events from a range of source depths (0 - 4 km), and (3) events from a variety of source types correlated with in-mine information such as pillar collapse and shear failure. Six months of data has been collected so far from the broadband seismic networks, and three months from the in-mine networks. We are exploiting the data set to improve U.S. operational capabilities to monitor for low-yield nuclear tests by analyzing the mining-induced events in a number of ways. We are gathering and analyzing events with M > 2.5, as well as some selected smaller events, including point explosions (mine blasts), mine-related stress release, mining activities, and shallow earthquakes. We are creating cataloged information on origin times and locations ground truth 0 (GT0), source parameters, focal mechanisms, coda-derived source spectra, coda magnitudes, local-to-regional phase propagation characteristics, relative P and S excitation, source apparent stress variation, and local-to-regional body-wave amplitude ratios that can discriminate between the different source categories.
Presented at the Monitoring Research Review (29th): Ground-Based Nuclear Explosion Monitoring Technologies held in Denver, Colorado on 25-27 September 2007. Published in the Proceedings of the Monitoring Research Review (29th): Ground-Based Nuclear Explosion Monitoring Technologies, p185-194, 2007. Sponsored by the National Nuclear Security Administration (NNSA) and the Air Force Research Laboratory (AFRL). The original document contains color images.