New Zealand Journal of Geology and Geophysics abstracts
Progress in understanding the paleoseismicity of the central and northern
Alpine Fault, Westland, New Zealand
MARK D. YETTON
Natural Hazards Research Center
Department of Geological Sciences
University of Canterbury
Private Bag 4800
Christchurch, New Zealand*
*Present address: Geotech Consulting Ltd, RD1, Charteris Bay, Lyttelton RD.
Abstract Radiocarbon dates from trenching of the Alpine Fault
trace at Crane Creek, between the Haupiri and Ahaura Rivers, demonstrate the
last earthquake rupture at this location occurred between AD 1480 and
1645, with associated local river aggradation and terrace formation. A second
trench 6 km farther north at Ahaura gives the same radiocarbon age for the
last event.
An enlarged record of radiocarbon ages for aggradation terraces and landslides
in central and north Westland has a group of dates which are a reasonable match
to the date range from the trenching. While this is compatible with regional
aggradation and landsliding associated with an Alpine Fault earthquake during
this period, this type of data cannot be used to demonstrate the dates were
synchronous or coseismic.
However, historical earthquakes have shown that, in steep forested terrain, an
earthquake causes extensive forest mortality, with a corresponding synchronous
period of regeneration. Recent information of forest age in Westland indicates
two such periods in the last 600 yr, and the most recent of these reflects
the earthquake rupture recorded in the trenches. This implies the earthquake
occurred at the young end of the trench date range at
c. AD 1600-1650.
Keywords Alpine Fault; central and northern Westland;
paleoseismology; trenching; neotectonics; radiocarbon; forest disturbance
New Zealand Journal of Geology & Geophysics, 1998, Vol. 41:
475-483
0028-8306/98/4104-0475 $7.00/0 (c) The Royal Society of New Zealand
1998
PDF file of entire paper: medium quality (811K); (scanned from paper original: notes about this process)
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