New Zealand Journal of Geology and Geophysics abstracts
Refined slip distribution and moment magnitude of the 1848 Marlborough earthquake, Awatere Fault, New Zealand
Dougal P. M. Mason*
Timothy A. Little
School of Earth Sciences
Victoria University of Wellington
PO Box 600
Wellington, New Zealand
Dougal.Mason@opus.co.nz
*Present address: Opus International Consultants Ltd, PO Box 12003, Wellington, New Zealand.
Abstract The Awatere Fault is an important element
of the obliquely convergent plate boundary zone in northeastern South
Island, New Zealand, and is comprised of two geomorphically distinct
sections that join across a complex fault junction in the upper Awatere
Valley. The Mw c. 7.5 Marlborough
earthquake of 1848 ruptured a c. 110 km length of the eastern
section of the Awatere Fault, from the South Island’s east coast
extending inland to at least Barefell Pass. This study attempts to
document the coseismic slip distribution during the 1848 earthquake
rupture. We examine a previously unmapped length of the fault trace in
the upper Awatere Valley, along which we measured as many small
(metre-scale) geomorphic displacements as possible. Based on these new
data, and previous observations of inferred 1848 slip on other parts of
the Awatere Fault, we infer that the 1848 earthquake had a mean
coseismic displacement of 5.3 ± 1.6 m, a surface rupture
length of 100–110 km, and a moment magnitude of Mw
= 7.4–7.7. This new moment magnitude estimate supports previous
estimates based on regressions of geometrical rupture parameters
inferred for the 1848 earthquake and attenuation models of felt
intensities. The set of second-smallest horizontal geomorphic
displacements (c. 8–15 m) are approximately double
those attributed to the 1848 earthquake, suggesting the penultimate
event was of a similar magnitude to the 1848 earthquake.
Keywords 1848 earthquake; Awatere Fault;
earthquake magnitude; Marlborough; New Zealand; paleoseismology;
strike-slip faults; South Island
G05041; Received 16 August 2005; accepted 9 June 2006; Online publication date 8 August 2006
New Zealand Journal of Geology & Geophysics, 2006, Vol. 49: 375–382
0028–8306/06/4903–0375 © The Royal Society of New Zealand 2006
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