International Geologiical Congress - Oslo 2008

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EIE-07 High-resolution geophysical imaging of geological structures and processes in environmental studies

 

Characterizing active faults using 3-D GPR data

 

Alastair McClymont, ETH Zurich (Switzerland)
Alan Green, ETH Zurich (Switzerland)
Pilar Villamor, GNS Science (New Zealand)
Heinrich Horstmeyer, ETH Zurich (Switzerland)
David Nobes, University of Canterbury (New Zealand)
 

 

Ground penetrating radar (GPR) has become an important tool for studying subsurface geometries of active faults. Because active faults are typically characterized by complicated near-surface structures that vary with the styles of faulting and the types of rock that are ruptured, the GPR data can be difficult to interpret. We have acquired 3-D GPR data sets across three active fault zones within New Zealand that have different deformation styles: the strike-slip Wellington Fault Zone, reverse faults of the Ostler Fault Zone, and normal faults of the Maleme Fault Zone. To improve our interpretation of the processed GPR volumes, we have employed two suites of geometric attributes. The first suite was computed using a coherence-based algorithm. It provided estimates of the coherency, azimuth, and dip of reflections. The second suite quantified the volumetric textures of reflections, which allowed different reflection facies to be defined objectively. We have demonstrated how some attributes were more successful at visualizing certain structural or depositional characteristics than others. For example, the coherency attribute was an excellent tool for highlighting normal faults within volcanic deposits of the Maleme fault zone, whereas the texture-based attributes were most useful for discriminating between the gravel and metasediment units juxtaposed by the Wellington Fault Zone. Our GPR data sets and associated attribute volumes showed details of near-surface fault geometry that were not evident from surface mapping and they revealed evidence for off-fault deformation and gravitational collapse structures.

 

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