Late Holocene displacements and characteristic earthquakes on the Hope River segment of the Hope Fault, New Zealand

Abstract

Abstract On the Hope River segment of the Hope Fault, west of Hanmer Springs, New Zealand, a 36 m dextral offset of a dated river terrace riser indicates an average local late Holocene horizontal slip-rate of 10.5 ± 0.5 m/kyr. A trench excavated across the fault in a nearby swamp revealed five silt layers within a 1.5 m thick column of peat. Radiocarbon dates and plant pollen indicate that the base of the swamp is approximately 700 years old, so peat has accumulated at an average rate of 2.35 ± 0.6 mm/yr. The youngest silt layer was probably derived from a landslide triggered during an M 7–7.3 earthquake in 1888 ad, and the older silt layers are attributed to similar prehistoric (pre-1850 ad) earthquakes. Pollen from the lowest silt shows brief local dominance of lacebark (Hoheria cf. H. lyalli) during a phase of former beech (Nothofagus) forest. Sharp increases in the percentage of matagouri (Discaria toumatou) pollen follow the younger silt layers, which were deposited during a later period of fire-indu...