HR: 15:30h
AN: NS14A-01    [Abstracts]
TI: Three-Dimensional Georadar Surveying of Active Faults
AU: * McClymont, A
EM: amcclymont@aug.ig.erdw.ethz.ch
AF: Institute of Geophysics, ETH-Hoenggerberg, Zurich, CH-8093 Switzerland
AU: Campbell, J
EM: jocelyn.campbell@canterbury.ac.nz
AF: Department of Geological Sciences, University of Canterbury PB 4800, Christchurch, New Zealand
AU: Corboz, P
EM: phcorboz@romandie.com
AF: Institute of Geophysics, ETH-Hoenggerberg, Zurich, CH-8093 Switzerland
AU: Grass, C
EM: grass@dplanet.ch
AF: Institute of Geophysics, ETH-Hoenggerberg, Zurich, CH-8093 Switzerland
AU: Green, A
EM: alan@aug.ig.erdw.ethz.ch
AF: Institute of Geophysics, ETH-Hoenggerberg, Zurich, CH-8093 Switzerland
AU: Gross, R
EM: ralf@aug.ig.erdw.ethz.ch
AF: Institute of Geophysics, ETH-Hoenggerberg, Zurich, CH-8093 Switzerland
AU: Holliger, K
EM: holliger@aug.ig.erdw.ethz.ch
AF: Institute of Geophysics, ETH-Hoenggerberg, Zurich, CH-8093 Switzerland
AU: Horstmeyer, H
EM: heinrich@aug.ig.erdw.ethz.ch
AF: Institute of Geophysics, ETH-Hoenggerberg, Zurich, CH-8093 Switzerland
AU: Nobes, D
EM: david.nobes@canterbury.ac.nz
AF: Department of Geological Sciences, University of Canterbury PB 4800, Christchurch, New Zealand
AU: Streich, R
EM: rita@aug.ig.erdw.ethz.ch
AF: Institute of Geophysics, ETH-Hoenggerberg, Zurich, CH-8093 Switzerland
AU: Tronicke, J
EM: jens@aug.ig.erdw.ethz.ch
AF: Institute of Geophysics, ETH-Hoenggerberg, Zurich, CH-8093 Switzerland
AU: Villamor, P
EM: p.villamor@gns.cri.nz
AF: Institute of Geological and Nuclear Sciences, PO Box 30368, Lower Hutt, New Zealand
AB: For reliable seismic hazard estimates and knowledge of the fundamental processes that govern surface rupturing earthquakes it is necessary to determine the locations and geometries of active faults, including those buried beneath recently deposited sediments. Although excavated trenches may supply important details on hidden faults, the subsurface volumes that can be examined in this manner are generally small. In an attempt to provide paleoseismologists with a non-invasive tool that will allow them to investigate regions between and beyond sparsely spaced trenches, we have developed cost-effective 3-D georadar data acquisition, processing and interpretation techniques. These techniques have been applied with varying degrees of success to a range of active strike-slip, normal, thrust and transpressional fault zones. Our 3-D georadar data across the northern San Andreas fault in California revealed, unexpectedly, the existence of two fault strands. An offset of a linear-trending feature suggested that 4.5 5.5 m of horizontal displacement had occurred on one of these strands, either during the 1906 San Francisco earthquake or earlier. Somewhat surprisingly, two fault stands were also detected in 3-D georadar data acquired across the Wellington strike-slip fault in New Zealand (NZ). The first-ever fault-plane reflections from an active strike-slip fault were observed in these data. Georadar data collected within the Taupo Volcanic Zone (NZ) contained two prominent parallel reflections that originated from the boundaries of Late Pleistocene lacustrine and tephra deposits. Distinct vertical offsets of these reflections allowed us to estimate displacements at individual normal fault strands across the entire inner graben of the Maleme Fault Zone. The total displacement represented by these offsets was roughly 10-20% greater than that inferred from geomorphological studies, demonstrating the limitations of surface observations for determining cumulative fault movements. In the Canterbury Plains west of Christchurch (NZ), the results of 3-D georadar surveying not only confirmed the location of a fault zone, the existence of which had been postulated on the basis of subtle geomorphological features, but also demonstrated that it comprised multiple strands. Finally, 3-D georadar data allowed us to map the detailed geometry of several thrust planes of the Ostler fault system (NZ).
DE: 7221 Paleoseismology
DE: 8010 Fractures and faults
SC: Near-Surface Geophysics [NS]
MN: 2005 Joint Assembly