ORIGIN OF SMALL-SCALE SEGMENTATION AND TRANSPRESSIONAL THRUSTING ALONG THE ALPINE FAULT, NEW-ZEALAND

The Alpine fault is the major structural feature of the Australian-Pac ific plate boundary in the South Island of New Zealand. Geologic evide nce suggests that half to three-quarters of the plate boundary displac ement is accommodated by movement on the fault. Detailed investigation of the central section of the Alpine fault has revealed that it consi sts of oblique thrust sections striking 020-degrees-050-degrees that a re linked by subvertical right-lateral faults striking between 065-deg rees and 090-degrees. The segmentation is on a scale of 1-10 km. Simil arly oriented right-lateral faults are abundant southeast of the Alpin e fault and are consistent with stresses induced in an elastic layer b y an oblique-slip ductile fault zone below. Propagation of the fault t o the surface is predicted to result in an en echelon arrangement of s trike-slip and thrust segments. It is suggested that the spatial distr ibution of segments is affected by the existence of deeply incised val leys in the hanging wall that disturb the stress field to depths of 1- 4 km. The segmentation is near surface and does not appear to act as a barrier to the propagation of large earthquakes.