Terrestrial and GPS measurements of deformation across the Taupo back arc and Hikurangi forearc regions in New Zealand

Abstract

Geodetic measurements of deformation across the Taupo back arc and Hikurangi forearc regions of New Zealand are derived from Global Positioning System (GPS) measurements made in 1990 and 1991 and triangulation observations made in the 1920s, 1950s, and 1970s. The GPS horizontal coordinate differences have precisions of 5-6 mm and the triangulation observations have precisions of 0.7-1.2 arc sec. These different kinds of observation allow simultaneous estimation of strain parameters and single-epoch coordinates for a total of 184 stations, at 68 of which GPS observations were made. Under the assumption that no shift of the scale or orientation of the GPS reference frame is embodied in the data from 13 GPS stations within the Taupo Volcanic Zone (TVZ) common to the 1990 and 1991 surveys, the rotational, dilatational and shear components of the deformation rate tensor within the TVZ can be estimated for that 1year interval. The principal extension rate from 1990 to 1991 is 0.21 _+0.09 x 166/yr (68% confidence) at an azimuth of 124_+ 13 ø, corresponding to 8_+4 mm/yr extension over 40 km. Neither the orthogonal principal extension rate, 0.02_+ 0.03 x 10-6/yr, nor the rotation rate, 0.06+0.04/•rad/yr, is significant. The dilatation rate of 0.23+_0.09 x 10'6/yr is therefore produced by uniaxial extension. The data from 75 stations distributed from behind the back arc region and well into the forearc region, which were surveyed in at least two of the triangulation or GPS epochs between the 1920s and 1991, allow the spatial variation of the shear components of the deformation rate tensor to be estimated. The maximum engineering shear rates lie in the range 0.1-0.2 x 10-6/yr within the TVZ and maintain these values, with similar orientations, in the forearc region to the east. The western and southern margins of active extension are reasonably well determined by changes in orientation and magnitude of the shear component. These results provide confirmation of the previously less well-determined deformation field, and in comparison with subduction models indicate that the surface deformation is reflecting variation from north to south of coupling of the subduction plate interface, and that both trench suction and gravitational collapse probably contribute to the extension in the forearc region. Paper number 94JB03265 0148-0227/95/94JB-03265505.00 triangulation observed mainly in the 1920s, 1950s, and 1970s. The GPS measurements were made jointly by the Geology and Geophysics), Victoria University of Wellington, University of Colorado at Boulder, and the University NAVSTAR Consortium (UNAVCO). As well as establishing new GPS sites for future reoccupation, these surveys occupied many of the trigonometric stations established by the Department of Survey and Land Information (DOSLI) (formerly Department of Lands and Survey) for the original first-order survey in the 1920s and 1930s, second-order surveys in the 1950s, and a dedicated survey for crustal deformation in the 1970s. These terrestrial data have previously been analyz...

Geodetic measurement of deformation in the Taupo Volcanic Zone, New Zealand: The north Taupo network revisited

“…Our spreading rates across the network are remarkab] similar to the Darby & Meertens (1995) result of 8 ± 4 mm yr at 124 ± 13°, derived from 1990-91 GPS surveys over the entire TVZ, and the Sissons (1979) result for the norther i TVZ of 8 ± 2 mm/yr. In contrast, we do not find that the orthogonal deformation is zero as those studies respectivel y measured and assumed.…”

“…43 6.320 6.300 6.280 6.260 fault trace • 1949-1986 station T 1986-1997 East (10 km) the assumption of no northeast-southwest deformation, the data immediately north of Lake Taupo failed to detect such a high rate of northwest-southeast extension (Darby & Meertens 1995). Newer GPS data reported here for the first time also fail to do so.…”

“…We have reprocessed the 1990 and 1991 GPS data used by Darby & Meertens (1995) as consistently as possible, together with data from 1993,1995, and 1997, some of which extend well beyond the north Taupo region. Generally, sites were occupied twice for either c. 7 h or 24 h with dual frequency geodetic receivers (Trimble 4000SSTs in 1990, and 1993Trimble 4000SSEs in 1995;TurboRogue SNR-8000s in 1997).…”

“…More specifically, the reader may consult Grindley (1960) for geology, Cole & Lewis (1981) for tectonics, Smith & Webb (1986) for seismicity, Stem (1985Stem ( ,1987 for heat flow, Darby & Meertens (1995) for geodetics, Bibby et al (1995) for resistivity and hydrothermal properties, and Smith et al (1989) for the plate tectonic significance of the TVZ. The earliest TVZ activity was andesitic and began at c. 2 Ma, followed by at least 31 caldera-forming rhyolitic eruptions since 1.6 Ma in its central part.…”

Evaluating the coastal deformation mechanisms of the Raukumara Peninsula, northern Hikurangi subduction margin, New Zealand and insights into forearc uplift processes

“…1B, C;Collot et al 1996). Geophysical and active fault studies suggest the upper forearc crust of the Raukumara Peninsula is undergoing margin-normal extension (Darby & Meertens 1995;Arnadottir et al 1999;Reyners & McGinty 1999;Berryman et al 2010). Analogies with comparable global examples, such as northern Chile (Clift et al 2003) and the Middle America Trench (Vannucchi et al 2004), would suggest parts of the Raukumara Peninsula forearc should be undergoing subsidence due to tectonic erosion removing material from the base of the overlying plate.…”