New Zealand Journal of Geology and Geophysics abstracts
Timing of late Holocene surface rupture of the Wairau Fault,
Marlborough, New Zealand
Judith Zachariasen*
Kelvin Berryman
Robert Langridge†
GNS Science
P.O. Box 30 368
Lower Hutt, New Zealand
Carol Prentice
Michael Rymer
US Geological Survey
345 Middlefield Rd
Menlo Park, CA 94025, USA
Mark Stirling
Pilar Villamor
GNS Science
Lower Hutt, New Zealand
*Present address: URS
Corporation, 1333 Broadway, Oakland, CA 94612, USA.
†Author
for correspondence: r.langridge@gns.cri.nz
Abstract Three trenches excavated across the
central portion of the right-lateral strike-slip Wairau Fault in South
Island, New Zealand, exposed a complex set of fault strands that have
displaced a sequence of late Holocene alluvial and colluvial deposits.
Abundant charcoal fragments provide age control for various
stratigraphic horizons dating back to c. 5610 yr ago.
Faulting relations from the Wadsworth trench show that the most recent
surface rupture event occurred at least 1290 yr and at most
2740 yr ago. Drowned trees in landslide-dammed Lake Chalice, in
combination with charcoal from the base of an unfaulted colluvial wedge
at Wadsworth trench, suggest a narrower time bracket for this event of
1811–2301 cal. yr BP. The penultimate faulting event occurred between
c. 2370 and 3380 yr, and possibly near 2680 ± 60 cal.
yr BP, when data from both the Wadsworth and Dillon trenches are
combined. Two older events have been recognised from Dillon trench but
remain poorly dated. A probable elapsed time of at least 1811 yr
since the last surface rupture, and an average slip rate estimate for
the Wairau Fault of 3–5 mm/yr, suggests that at least 5.4 m
and up to 11.5 m of elastic shear strain has accumulated since the
last rupture. This is near to or greater than the single-event
displacement estimates of 5–7 m. The average recurrence interval
for surface rupture of the fault determined from the trench data is
1150–1400 yr. Although the uncertainties in the timing of faulting
events and variability in inter-event times remain high, the time
elapsed since the last event is in the order of 1–2 times the average
recurrence interval, implying that the Wairau Fault is near the end of
its interseismic period.
Keywords active tectonics; earthquakes;
strike-slip faults; Holocene; Wairau; Marlborough; neotectonics;
charcoal; paleoseismicity; South Island; NZMS 260 N29, O28
G05045; Received 30 August 2005; accepted 27 September 2005; Online
publication date 3 March 2006
New Zealand Journal of Geology & Geophysics, 2006, Vol. 49:
159–174
0028–8306/06/4901–0159 © The Royal Society of New Zealand 2006
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