New Zealand Journal of Geology & Geophysics abstracts
Paleoseismicity and mass movements interpreted from
seismic-reflection data, Lake Tekapo, South Canterbury, New Zealand
Phaedra Upton
Erich C. Osterberg*
Department of Geology
University of Otago
PO Box 56
Dunedin 9054, New Zealand
phaedra.upton@stonebow.otago.ac.nz
*Present address: Department of Earth Sciences,
Dartmouth College, 6105 Fairchild Hall, Hanover, NH 03755, USA.
Abstract A 61 km seismic survey of Lake
Tekapo was shot in
2001 to identify tectonic features observed onshore. The survey
revealed bedrock highs, lake-floor offsets, and a series of mass
movement deposits, all interpreted to result from tectonic uplift and
paleoearthquake events. Fine-grained sediment within the lake basin,
imaged as uniform, regular-spaced, laminated reflectors, is at least
145 m thick at the southeastern end of the lake. Bedrock highs
(>70 m of relief) are found along-strike of the Irishman Creek Fault
and Forest Creek Faults, and are interpreted as long-term features that
are repeatedly raised in earthquakes and lowered by glaciers. Movement
on them since the last glacial maximum has offset the lake floor by
10–20 m, consistent with estimated uplift rates on these faults from
previous studies. The seismic reflection data suggest that both faults
extend into the centre of the lake, terminating against a
north–south-oriented structure, possibly the Tekapo River Fault. Mass
movement deposits are observed within the sediment pile, and we
attribute them to paleoearthquakes on local faults or the more distant
plate boundary. Using a sedimentation rate of 8 mm/yr, we date two sets
of mass movement deposits at 1720 ± 344 yr BP and 2810 ±
562 yr BP.
Keywords Lake Tekapo; seismic reflection;
Mackenzie Basin;
faults; tectonics; deformation
G07016; Online publication date 10 October 2007; Received 9 July
2007; accepted 17 September 2007
New Zealand Journal of Geology & Geophysics, 2007, Vol. 50:
343–356
0028–8306/07/5004–0343 © The Royal Society of New Zealand 2007
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