Late Quaternary displacements on the Hope Fault at Glynn Wye, North Canterbury

Abstract

Abstract An earthquake in 1888 generated surface rupture on the Hope Fault at Glynn Wye, North Canterbury, New Zealand, where earlier displacements are preserved as dextrally offset late Pleistocene glacial moraine and river terraces. The moraine and terraces are located at the eastern end of a >1 km wide sag basin named Poplars Graben, developed at a releasing bend in the Hope Fault. The offset landforms at Poplars Graben are fortuitously located to preserve a cumulative record of the local variability of finite strain within the Hope Fault zone. The landforms are of near-equal age (17 000 ± 2000 years), but the measured fault displacements across these features are different. Variations in displacement along the fault result from the total being partitioned into vector components of strike-parallel, strike-normal, and vertical slip, which are systematically related to changes in fault strike. This exemplifies the importance of understanding the geometry and kinematics of faults and fault systems when evaluating slip rates obtained from individual locations. The offset moraine, which is relatively free of structural complications, is used to calculate a slip rate of 14 ± 3 mm/yr for the last 17 000 ± 2000 years at this locality on the Hope Fault.