Geodetic analysis of horizontal crustal deformation within the northern South Island, New Zealand

Author:

Henderson, Christopher Mark.

Year:

Project type:

Subject:

Advisers:

Abstract:

A number of techniques are reviewed with the intention of identifying the best method for deformation analysis. The method finally adopted for deformation analysis consists of two data reduction steps. Firstly, the geodetic observation data are used to adjust the survey station coordinates. In the second step the results of the first step in conjunction with a model for the deformation are used to estimate the motion within the region. Statistical testing is emphasised throughout the coordinate adjustment phase and the deformation modelling procedure. Estimates for strain and rotation rates are presented in a different fashion to those of previous studies; contours of the measurements are superimposed on their error .surfaces. This allows improved accuracy in reading the results of the analyses. Statistical testing shows that the deformation within Marlborough is statistically compatible with a constant station velocity model. This indicates that variations of station velocity over the time between the first and last surveys are insignificant. Inhomogeneous analysis (polynomial modelled velocity) is found to be superior to the method of forming many homogeneous strain rate estimates. Polynomial based deformation models appear to be a reasonable representation of motion within regions where survey stations are evenly spaced and where the discontinuous part (eo-seismic deformation) of the velocity surface is much smaller than the continuous part (inter-seismic deformation). In regions where survey stations are not evenly distributed or the complexity of the polynomial model is not easily adjusted to the amount of available information, then connected low-order polynomial surfaces appear to be a reasonable method of modelling the motion. The results of the analyses suggest a shear strain rate maximum over the Clarence and Awatere faults. Most of the Marlborough Fault Zone east of the Wairau Fault is experiencing shear strain rates of at least 3 x 10-7 I year. Generally the shear strain rate results are compatible with previous geodetic shear strain rate estimates within the region. Dilatational strain rate estimates are generally of low precision, however, significant variations of the dilatation rate surface are found. The geodetic results indicate that rotation rates are progressiyely more clockwise towards the west within the southern portion of the Marlborough Fault Zone. This trend is not carried on into Marlborough, where the relative rotation becomes progressively more clockwise towards the south. The orientation of the principal axis of horizontal s~ear strain over most of the study region is found to be statistically compatible with a model of shear strain release on the major faults. However, average inter-seismic shear strain rates, estimated from the slip-rates of major faults, are incompatible with the geodetic measurements. The geodetic measurements of dilatational strain rate are also found to be generally incompatible with the shape of the dilatational strain rate surface approximated from uplift rates. A different relationship ' between tectonic rotation rates and geodetic measurements from that described by Lamb (1987) is presented. Estimated relative tectonic rotation rates are found to be of very low precision and are not statistically significant. The total relative velocity over the Marlborough

Named Localities:

Thesis description:

179 leaves : ill., maps ; 30 cm.

Department:

OU geology Identifier:

1995Henderson

Author last name:

OURArchive handle:

OURArchive access level:

Files

http://download.otagogeology.org.nz/temp/Abstracts/1995Henderson.pdf

Collection

Citation

Henderson, Christopher Mark., “Geodetic analysis of horizontal crustal deformation within the northern South Island, New Zealand,” Otago Geology Theses, accessed February 13, 2025, https://theses.otagogeology.org.nz/items/show/309.

Output Formats