New Zealand Journal of Geology and Geophysics abstracts
Paleoseismicity of the Rotoitipakau Fault Zone, a complex normal fault in the
Taupo Volcanic Zone, New Zealand
KELVIN BERRYMAN
SARAH BEANLAND*
Institute of Geological & Nuclear Sciences
P.O. Box 30 368
Lower Hutt, New Zealand
STEVEN WESNOUSKY
Department of Geological Sciences
University of Nevada
Reno, Nevada 89557, USA
Abstract Trenching of 6 of the 10 fault strands that comprise
the 5 km long, 1 km wide Rotoitipakau Fault Zone, Taupo Volcanic
Zone, New Zealand, shows that surface rupture has occurred at least eight times
in the zone during the past 8500 yr. Single-event displacements on each
strand vary from a few decimetres to perhaps more than 2.5 m, and there
may have been as much as 4.5-5.0 m of cumulative slip on several strands
in a single event. Five airfall tephra whose ages span the past 8500 yr
provide time lines within which cumulative slip rate has varied by
approximately 10 times: from 1-2.5 mm/yr in the period from the
AD 1886 Tarawera Tephra to the present, and in the c. 4000 yr
period from the 4.8 ka Whakatane Tephra to the 0.65 ka Kaharoa
Tephra; to 11 mm/yr in the c. 500 yr period from 0.65 ka to
AD 1886. All but one of the fault strands are downthrown to the southeast,
suggesting that the fault zone is part of the western margin of the Whakatane
Graben. This short fault zone may therefore be a splay of the Braemar Fault
Zone, and the very large displacement:length ratios characteristic of fault
rupture in this fault zone may be misleading if the fault connects to the
southwest with the Braemar Fault. Alternatively, faults in this
volcano-tectonic province may exhibit different surface faulting
characteristics than normal faults in nonvolcanic regions where most of the
fault parameter scaling relationships have been developed. Large
displacement:length ratios are a characteristic of fracturing above dike
intrusions. Such fracturing is accompanied by well-defined grabens and
single-episode (monogenetic) formation. In the Rotoitipakau Fault Zone, the
lack of graben development, and polygenetic movement history, indicates the
fault zone is a primary tectonic feature.
Keywords normal fault; earthquake geology; paleoseismicity;
Taupo Volcanic Zone; Whakatane Graben
New Zealand Journal of Geology & Geophysics, 1998, Vol. 41:
449-465
0028-8306/98/4104-0449 $7.00/0 (c) The Royal Society of New Zealand
1998
PDF file of entire paper: medium quality (3005K); (scanned from paper original: notes about this process)
This year's abstracts |
Journal home page |
All abstracts |
Publishing home page
