T23D-2979
Characterising the Alpine Fault Damage Zone using Fault Zone Guided Waves, South Westland, New Zealand
Tuesday, 15 December 2015
Poster Hall (Moscone South)
Jennifer Dawn Eccles1, Anton Gulley2, Carolin Morag Boese3, Peter E Malin4, John Townend5, Clifford H Thurber6, Bin Guo7 and Rupert Sutherland5,8, (1)The University of Auckland, Auckland, New Zealand, (2)University of Auckland, Auckland, New Zealand, (3)International Earth Sciences IESE Lt., Auckland, New Zealand, (4)ASIR Seismic, Dallas, TX, United States, (5)Victoria University of Wellington, Wellington, New Zealand, (6)Univ Wisconsin-Madison, Madison, WI, United States, (7)University of Wisconsin Madison, Madison, WI, United States, (8)GNS Science, Lower Hutt, New Zealand
Abstract:
Fault Zone Guided Waves (FZGWs) are observed within New Zealand’s transpressional continental plate boundary, the Alpine Fault, which is late in its typical seismic cycle. Distinctive dispersive seismic coda waves (~7-35 Hz), trapped within the low-velocity fault damage zone, have been recorded on three component 2 Hz borehole seismometers installed within 20 m of the principal slip zone in the shallow (< 150 m deep) DFDP-1 boreholes. Near the central Alpine Fault, known for low background seismicity, FZGW-generating microseismic events are located beyond the catchment-scale strike-slip and thrust segment partitioning of the fault indicating lateral connectivity of the low-velocity zone immediately below the near-surface segmentation. Double-difference earthquake relocation of events using the dense SAMBA and WIZARD seismometer arrays allows spatio-temporal patterns of 2013 events to be analysed and the segmentation and low velocity zone depth extent further explored. Three layer, dispersion modeling of the low-velocity zone indicates a waveguide width of 60-200 m with a 10-40% reduction in S-wave velocity, similar to that inferred for the fault core of other mature plate boundary faults such as the San Andreas and North Anatolian Faults.
