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 tHoheria cf. H. lyalli) during a phase of former beech (Nothofagus) forest. Sharp increases in the percentage of matagouri tDiscaria toumatou) pollen follow the younger silt layers, which were deposited during a later period of fire-induced shrubland. Both lacebark and matagouri are vigorous colonisers of bared ground, and matagouri presently forms the dominant plant cover on fault scarps and landslides known to have been bared during the 1888 earthquake. We infer that this pattern of plant succession on bared sites has followed repeated surface rupture along this segment of the Hope Fault. The vertical spacing of the silt layers, and our calculated mean peat accumulation rate, indicate a recurrence interval for silt deposition of 81-200 years, and support a model proposing that the 1888 earthquake was a characteristic event for the Hope River segment of the Hope Fault.

, an earthquake of probable magnitude M7-7.3 struck the Amuri District of North Canterbury, 100 km northwest of Christchurch, New Zealand, The earthquake ruptured a segment of the Hope Fault, and damaged buildings over a wide area, The effects of the earthquake indicate Modified Mercalli intensities of MM IX in the epicentral area, High-intensity isoseismals (>MM VII) were strongly elliptical and parallel to faulting, apparently attenuating steeply to the northwest and southeast, respectively. However, in parts of Greymouth and Christchurch, shaking was amplified (to MM VII), presumably by local ground conditions. After the earthquake, dextral offsets of between 1.5 and 2.6 m were observed on fencelines crossing the Hope Fault at four localities in the Hope Valley. Recent field work has indicated that the ruptured section forms a struc"turally distinct segment-the Hope River Segment-of the fault. It extends 30 ±5 km along the Hope Valley, between two basins developed at releasing bends in the Hope Fault zone. I infer that the earthquake was initiated beneath the Hope-Boyle Basin at the western end of the Hope River Segment, and propagated eastward until it was stopped in the Hanmer Basin. These inferences are supported by contemporary accounts of the effects of the earthquake, and are consistent with observations of earthquake faulting documented in recent international studies.

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 narnedPoplars 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.

S U M M A R YThe North Canterbury region marks the transition from Pacific plate subduction to continental collision in the South Island of New Zealand. Details of the seismicity, structure and tectonics of this region have been revealed by an 11-week microearthquake survey using 24 portable digital seismographs. Arrival time data from a well-recorded subset of microearthquakes have been combined with those from three explosions at the corners of the microearthquake network in a simultaneous inversion for both hypocentres and velocity structure. The velocity structure is consistent with the crust in North Canterbury being an extension of the converging Chatham Rise. The crust is about 27 km thick, and consists of an 11 km thick seismic upper crust and 7 km thick seismic lower crust, with the middle part of the crust being relatively aseismic. Seismic velocities are consistent with the upper and middle crust being composed of greywacke and schist respectively, while several lines of evidence suggest that the lower crust is the lower part of the old oceanic crust on which the overlying rocks were originally deposited.The distribution of relocated earthquakes deeper than 15 km indicates that the seismic lower crust changes dip markedly near 43"s. To the south-west it is subhorizontal, while to the north-east it dips north-west at about lo". Fault-plane solutions for these earthquakes also change near 43"s. For events to the south, P-axes trend approximately normal to the plate boundary (reflecting continental collision), while for events to the north, T-axes are aligned down the dip of the subducted plate (reflecting slab pull). While lithospheric subduction is continuous across the transition, it is not clear whether the lower crust near 43"s is flexed or torn.