HR: 0800h
AN: S41B-0967    [Abstracts]
TI: Near-Field High-Resolution Seismic, Strain and Displacement Measurements for Earthquake Source Studies in Deep Mines in South Africa
AU: * Johnston, M J
EM: mal@usgs.gov
AF: U. S. Geological Survay, 345 Middlefield Rd., MS977, Menlo Park, CA 94025 United States
AU: Reches, Z
EM: reches@ou.edu
AF: University of Oklahoma, 731 Elm Avenue, Norman, OK 73019 Israel
AU: van Aswegan, G
EM: gerrie@issi.co.za
AF: ISSI, P.O. Box 12063 , Die Boord, 2501 South Africa
AU: McGarr, A
EM: mcgarr@usgs.gov
AF: U. S. Geological Survay, 345 Middlefield Rd., MS977, Menlo Park, CA 94025 United States
AU: Lockner, D
EM: lockner@usgs.gov
AF: U. S. Geological Survay, 345 Middlefield Rd., MS977, Menlo Park, CA 94025 United States
AU: Sellers, E
EM: ESellers@csir.co.za
AF: MinTek, PO Box 91230, Auckland Park, 2006 South Africa
AU: Ben Zion, Y
EM: benzion@terra.usc.edu
AF: USC, Dept. Earth Sciences, Los Angeles, CA 90089 United States
AU: Williams, C
EM: colin@usgs.gov
AF: U. S. Geological Survay, 345 Middlefield Rd., MS977, Menlo Park, CA 94025 United States
AB: Unique access to information on the physics of the earthquake source (earthquake nucleation, fault rupture, heat generation, stress state, seismic wave propagation, fault displacement, material properties and particularly changes in some of these parameters prior to rupture) exists in the near-field of mining-induced earthquakes in deep gold mines in South Africa. The new NSF funded Natural Earthquake Laboratory in South African Mines (NELSAM) will provide seismic velocity/acceleration, ground strain, temperature, fault displacement, acoustic emission (AE), and perhaps self-potential (SP) data in small 3-D arrays across and within active faults in two different mines. 3-component accelerometers to be installed in or near the faults have a range from micro g to 0.5 g in the band 0.05 - 500 Hz. Fault displacement meters (creepmeters) to be installed at low angles across faults within boreholes have a range of microns to 0.2 m and cover the frequency range from DC to 100 Hz. Successful measurement of total displacement will depend on the creepmeter reference length surviving the fault rupture. Temperature will be measured to millidegrees C at points within, and at increasing distances from fault zones, to capture the heat generated by future and past earthquakes. Strain transients will be measured with 3-component near-fault borehole strainmeters with capacitance displacement transducers providing a resolution < 10E-9. 3-component seismic velocity transducers will be installed together with each accelerometer and supplement the current mine seismic network. AE and SP will be measured within boreholes crossing faults if recording capability is sufficient. All data will be digitally sampled and transmitted to the surface in real-time for analysis to focus on unraveling the physics of the nucleation process, non-linear deformation prior to rupture, propagating aseismic slip, and variation in the material properties of near-fault materials (e.g. state/rate dependent friction). Similar high-resolution borehole strain and seismic networks on the San Andreas fault system in California can make measurements no closer than 5 km from moderate to large earthquakes on these faults. However, these San Andreas data do provide a reference set for comparison with pre-event strain levels, earthquake nucleation moments, coseismic strains, aseismic slip events ("slow" earthquakes), fault creep events, changes in fault zone material properties and the basic rupture nucleation process.
DE: 8199 General or miscellaneous
DE: 7220 Oceanic crust
DE: 8110 Continental tectonics--general (0905)
DE: 7209 Earthquake dynamics and mechanics
DE: 7215 Earthquake parameters
SC: Seismology [S]
MN: 2004 AGU Fall Meeting