Crustal strain across the marlborough faults, New Zealand

Abstract

The shear strain across the Marlborough district was determined by comparison of the angles observed in the low-accuracy triangulation survey of 1878 to 1884 with those of the second and third order survey made between 1951 and 1960: The shear strain is significantly non-zero across a zone about 100 km wide, with a mean rate over the 70-year interval of 0·5 ± 0·1 7#x00B5;rad/year. Shear strain is not concentrated near the Wairau, Awatere, or Clarence Faults, which indicates that little or no slip has occurred on these faults between the surveys. On the Hog Swarnp Fault, however, the concentration of shear strain is consistent with a right lateral displacernent of about 300 mm. The azimuth of the principal axis of shortening varies between 1000 and 128°, and is consistent with the post-glacial right lateral strike-slip movement known to have taken pl ace on each of the faults. The axis of shortening also agrees with the principal axis of compressive stress determined from microearthquake studies in the area. The total annual movement across the Marlborough shear zone is estimated to be between 25 mm and 45 mm.