New Zealand Journal of Geology and Geophysics abstracts
Refinements to the paleoseismic chronology of the eastern Awatere
Fault from trenches near Upcot Saddle, Marlborough, New Zealand
Dougal P. M. Mason1
Timothy A. Little
School of Earth Sciences
Victoria University of Wellington
PO Box 600
Wellington, New Zealand
dougal.mason@opus.co.nz
1Present address: Opus International Consultants Ltd,
PO Box 12003, Wellington, New Zealand.
Russell J. Van Dissen
GNS Science
PO Box 30368
Lower Hutt, New Zealand
Abstract The Awatere Fault is one of four
principal strike-slip faults within the obliquely convergent plate
boundary zone in northeastern South Island, New Zealand. The eastern
section of the fault last ruptured in 1848, in the Mw c.
7.5 Marlborough earthquake, when surface rupture was traced by
first-hand accounts from the South Island’s east coast inland to
Barefell Pass (c. 110 km). We excavated two paleoseismic trenches
near Upcot Saddle on the eastern section of the fault, c. 70 km
inland from the coast. Interpretation of crosscutting relationships
between sediments exposed in these trenches, in association with 21
radiocarbon dates, suggest at least 5, and possibly 6, events have
ruptured this part of the Awatere Fault in the last 5600 yr. These
events include a young rupture (<300 cal. yr BP) that is presumed to
be the surface rupture of the 1848 Marlborough earthquake. The Upcot
Saddle rupture history is combined with paleoseismic data from two
previous trenches, located c. 55 km to the northeast at Lake
Jasper, to infer a chronology of 9–10 events between AD 1848 and
8610 cal. yr BP on the eastern section. These 9–10 events define
a mean recurrence interval of 820–950 cal. yr on that fault,
which is within error of the mean recurrence interval calculated using
available data on late Quaternary slip rates (6 ± 2 mm/yr)
and mean coseismic slip during the 1848 earthquake (5.3 ±
1.6 m). The intervals between individual paleoearthquakes on the
eastern section are non-uniform, and range from 220–620 to
1540–2120 yr.
Keywords 1848 earthquake; Awatere Fault;
earthquakes; Marlborough; New Zealand; paleoseismology; radiocarbon
dates; recurrence interval; strike-slip faults; South Island; trench
G05029; Received 4 July 2005; accepted 3 July 2006; Online publication date 8 August 2006
New Zealand Journal of Geology & Geophysics, 2006, Vol. 49: 383–397
0028–8306/06/4903–0383 © The Royal Society of New Zealand 2006
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