A new geodetic estimate of deformation in the Central Volcanic Region of the North Island, New Zealand

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Abstract
Deformation immediately north of Lake Taupo in the Central Volcanic Region of the North Island, New Zealand, is shown from repeated geodetic surveys to vary in both orientation and magnitude. While the relatively extensional direction is nearly east‐west in the west of the region, the northeast‐southwest dextral shear component increases eastward, so that the relatively extensional direction becomes nearly north‐south in the east of the region. The magnitude of maximum engineering shear strain varies spatially between 0.4 and 1.0 × 10‐6/yr. Previous geodetic analyses have not had sufficient spatial resolution to study this type of variation. Under an assumption of no length change parallel to the trend of faulting, the extension rate across a 40 km zone north of Lake Taupo is estimated to be 18 ± 5 (1 s.e.) mm/yr. This is consistent with an upper bound of 20–30 mm/yr for the last 4 Ma, from the age distribution of low‐potash andesites, and is significantly greater than previous geodetic estimates. The deformation is generally consistent with geological inferences, but not necessarily with seismological data from earthquakes below magnitude 5, which are themselves difficult to interpret consistently.