New Zealand Journal of Geology and Geophysics abstracts
Geodetic measurement of deformation in the Taupo Volcanic Zone,
New Zealand: the north Taupo network revisited
DESMOND J. DARBY
KATHLEEN M. HODGKINSON
GRAEME H. BLICK*
Institute of Geological & Nuclear Sciences
P.O. Box 30368
Lower Hutt, New Zealand
*Present address: Land Information New Zealand, Wellington, New Zealand.
Abstract A previous geodetic estimate of 18 mm/yr horizontal
extension for the Taupo Volcanic Zone (TVZ) immediately north of Lake Taupo for
the period 1949-86 is re-examined for several reasons: this rate has not been
confirmed by GPS surveys in the 1990s; newly compiled precise levelling data
now allow us to estimate the extent of non-tectonic deformation attributable to
the Wairakei geothermal field; and the precise levelling and lake-levelling
data reveal a spatial variation in tectonic subsidence that casts doubt on the
earlier assumption of homogeneous horizontal strain. We use the vertical and
horizontal data to derive a Mogi point source model for the geothermal field,
and this model allows us to correct the observed horizontal velocities of
survey points. Statistical analysis of the corrected horizontal velocities
shows that the strain across the TVZ is not homogeneous. When these factors are
accounted for, an extension rate of 8 +/- 2 mm/yr (1 SE) can be applicable
for both 1949-86 and 1986-97. This is about half the previous estimate, which
we now consider to be incorrect. The distribution of deformation differs
between these periods, and the seismicity of the region shows temporal
variations on a similar time-scale (decades). The extension rate is much
greater than can be accounted for by seismic strain release, and the occurrence
of historical earthquakes up to M = 6 indicates that a significant part
of the measured extension represents seismic strain accumulation. The spatial
heterogeneity of the strain partitions the region identically to that derived
from geological studies of fault activity. In particular, there is a spatial
concentration of extension and tilt about the Whangamata fault system.
Keywords geodesy; Taupo Volcanic Zone; triangulation;
levelling; rifting
New Zealand Journal of Geology & Geophysics, 2000, Vol. 43:
157-170
0028-8306/00/4302-0157 $7.00/0 (c) The Royal Society of New Zealand
2000
PDF file of entire paper: medium quality (1418K); (scanned from paper original: notes about this process)
This year's abstracts |
Journal home page |
All abstracts |
Publishing home page
