HR: 08:45h
AN: S31B-04    [Abstracts]
TI: The Rupture Zone of the M=2.2 Earthquake that Reactivated the Ancient Pretorius Fault in TauTona Mine, South Africa
AU: * Heesakkers, V
EM: vincent.heesakkers-1@ou.edu
AF: School of Geology and Geophysics, University of Oklahoma, 100 E Boyd St., Norman, OK 73019 United States
AU: Murphy, S K
EM: skmurphy@anglogoldashanti.com
AF: ISS International, Western Deep, Carletonville, 2605 South Africa
AU: van Aswegen, G
EM: gerrie@issi.co.za
AF: ISS International, Western Deep, Carletonville, 2605 South Africa
AU: Domoney, R
EM: rdomoney@uwc.ac.za
AF: Earth Science Department, University of Western Cape, Private Bag X17, Belleville, 7535 South Africa
AU: Addams, S
EM: sgadams@webmail.co.za
AF: Earth Science Department, University of Western Cape, Private Bag X17, Belleville, 7535 South Africa
AU: Dewers, T
EM: tdewers@ou.edu
AF: School of Geology and Geophysics, University of Oklahoma, 100 E Boyd St., Norman, OK 73019 United States
AU: Zechmeister, M
EM: zechmeim@ou.edu
AF: School of Geology and Geophysics, University of Oklahoma, 100 E Boyd St., Norman, OK 73019 United States
AU: Reches, Z
EM: reches@ou.edu
AF: School of Geology and Geophysics, University of Oklahoma, 100 E Boyd St., Norman, OK 73019 United States
AB: The M=2.2 earthquake of December 12, 2004, reactivated segments of the Archean Pretorius fault in TauTona mine, South Africa. We mapped the 3D structure of the rupture zone of this event at depth of 3.6 km in pre-earthquake damaged tunnels, as well as post-earthquake new tunnels. The Pretorius fault is a dormant, 10 km long ENE trending fault with a right-lateral displacement up to 200 m, and vertical displacement of 30-60 m. The fault zone is 25-30 m wide with tens of anastomosing segments; many of the segments display veins of sintered cataclasite (Zechmeister et al., this meeting). The M=2.2 rupture zone reactivated two quasi-planar, crosscutting segments within the Pretorius fault zone; one is a fault segment, oriented 43/167 degrees, and the second is a bedding surface, oriented 20/161 degrees. The reactivated segments were traced horizontally to 25 m and 5 m vertically; this is a minimum size limited by available tunnels. Both segments display sintered cataclasite veins of 1-6 cm thick. The event rupturing formed fresh fine-grained "rock powder" that appear in 1-5 thin zones that are 0.5-1.0 mm thick each. The rock powder zones dominantly appear along the contacts between the sintered cataclasite and the quartzitic host rock. The rupture zone is accompanied by a set of vertical, secondary tensile fractures (wing cracks) in the hanging wall. Displaced rock-bolts reveal 10 mm and 25 mm of normal-dextral slip with rake of 23 and 35 degrees. Our measurements of in-situ stresses in two shallow holes, located 60 m and 35 m from the rupture zone, reveal that sigma-HMAX is oriented 336 degrees, and its magnitude is 60-90 MPa; this value approaches the vertical stress of 97 MPa. We will discuss the relationships between this in-situ stress state and the geometry of the rupture zone, and we will also discuss the rupture energy of the event and its relations to the moment energy derived from seismic data.
UR: http://earthquakes.ou.edu
DE: 7209 Earthquake dynamics (1242)
DE: 8004 Dynamics and mechanics of faulting (8118)
DE: 8034 Rheology and friction of fault zones (8163)
DE: 8118 Dynamics and mechanics of faulting (8004)
SC: Seismology [S]
MN: Fall Meeting 2005