Search

The International Union of Geological Sciences (IUGS) was formed in 1961 as the umbrella organisation to represent the geosciences globally. It is a non-political, non-governmental and a not-for-profit organization with 120 member countries, which: 1. Promotes development of the geosciences through the support of international, broad-based, and interdisciplinary scientific studies relevant to the entire System Earth; 2. Applies the results of these and other studies to preserving Earth’s natural environment, using all natural resources wisely and improving the prosperity of nations and the quality of human life; 3. Strengthens public awareness of geology and advances geological education in the widest sense; 4. Develops and promulgates geoscience standards, including for information management and chronostratigraphy; and 5. Through its membership of the International Council for Science (ICSU), has good links to a wide range of scientific and technical expertise.

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

In this project, we are developing and exploiting 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 is being 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. After a year of seismic monitoring of mine activity (2007), over 10,000 events in the range -3.4 < ML < 4.4 have been catalogued and recorded by the in-mine networks. 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. We have analyzed in-mine recordings in detail at one of the South African mines (Savuka) to (i) improve on reported hypocentral locations, (ii) verify sensor orientations, and (iii) determine full moment tensor solutions. Hypocentral relocations on all catalogued events have been obtained from P- and S-wave travel-times reported by the mine network operator through an automated procedure that selects travel times falling on Wadati lines with slopes in the 0.6-0.7 range; sensor orientations have been verified and, when possible, corrected by correlating P-, SV-, and SH-waveforms obtained from theoretical and empirical (polarization filter) rotation angles; full-moment tensor solutions have been obtained by inverting P-, SV-, and SH-spectral amplitudes measured on the theoretically rotated waveforms with visually assigned polarities., Proceedings of the Monitoring Research Review: Ground-Based Nuclear Explosion Monitoring Technologies (30th) held in Portsmouth, VA on 23-25 Sep 200. Sponsored by the National Nuclear Security Administration (NNSA) and the Air Force Research Laboratory (AFRL). The original document contains color images.

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.