The Conway Segment of the dextral-slip Hope Fault is one of the fastest slipping fault segments along New Zealand's plate boundary, but has not ruptured co-seismically in the historic period and little paleoseismic data exist to constrain its large earthquake record. Two paleoseismic trenches were opened adjacent to Greenburn Stream near Kaikoura for the 2001 ILP Paleoseismology Conference. Both trenches were excavated into deposits ponded against an uphill-facing shutter scarp. Trench 1, dug through a cobbly soil and surface deposit was dominated by a thick fan/fluvial sequence that was radiocarbon dated at 4409 ± 60 C 14 years BP (4844-5288 cal years BP) at the base of the trench. This trench exhibited evidence of complex deformation from many paleoseismic events. The most recent earthquakes are difficult to constrain due to a lack of cover stratigraphy on the fan deposits. However, the modern soil appears to be faulted and is covered by cobbles with a weathering rind-derived age of 220 ± 60 years. Trench 2, dug 50 m to the west has an expanded sequence of the younger cover deposits. Paleoseismic event horizons have been recognised from the combined evidence of upwardterminating faults, offset and mismatched units, a sandblow deposit, and abrupt landscape change shown by the burial of paleosol surfaces that form the event horizons. Two paleosols underlying the modern soil are clearly faulted by two separate rupture events. A dome of sand interpreted as a liquefaction sandblow deposit overlies the lower paleosol (event horizon). Both paleosols are overlain by metre-thick debris deposits, interpreted as earthquake-induced rock avalanches that cascaded off the hillslope following Mw 7 + events. Four radiocarbon dates place some constraints on the timing of the three recent surface-rupturing events. The youngest and lowest date is 548 ± 60 C 14 years BP (504-656 cal years BP) and occurs below the lower paleosol. It constrains the maximum duration of time in which the last 2 earthquake events occurred to be 545 years (1295-1840 A.D.). This is consistent with the average Recurrence Interval (RI) of 180-310 years that we determine using two independent paths. The soil record indicates that each event is separated by a significant period of time, comparable to the calculated RI. The most recent event is constrained between ca. 1780 A.D. ± 60 years, taking into account the dates from these trenches, a weathering rind age, and from stratigraphic correlation at the site. Event III probably occurred before 1220 A.D. A maximum dextral slip rate of 23 ± 4 mm/yr is calculated from the minimum fan age and the offset/deflection of a stream channel along the shutter ridge. In concert with the estimate of single event displacement (5-6 m), these results show that the Conway Segment of the Hope Fault is fast-slipping and has ruptured regularly as a result of large earthquakes prior to the European colonisation of New Zealand.

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The Southern Ridge Cutback 3 (STR3) at the Tom Price mine site will be the highest and steepest slope in Rio Tinto Iron Ore's Pilbara operation. Initial geotechnical assessment of the STR3 western slope using two-dimensional limit equilibrium methods recommended a substantial flattening of the design. This would have resulted in the deferral of 3.2 Mt of high grade ore. Given the good performance of the preceding STR2 cutback, it was considered that the two-dimensional (2D) analysis results were not representative of the expected stability and were overly conservative. Structures constraining the dominant mode of instability strike oblique to the slope. This aspect and the effects of 3D lateral confinement are not considered by 2D analysis. In order to address this, a 3D modelling project was initiated with development of a 3D model by Itasca Australia Pty Ltd.The 3D model method utilises both 3DEC™ (Itasca 2013a) and FLAC3D™ (Itasca 2012) software to develop a constitutive model that takes into account the dominant bedding anisotropy within the slope. As this was the first such model developed for Rio Tinto Iron Ore (RTIO), an external review board was appointed to provide technical guidance during the project. Sensitivities were carried out to address questions regarding in situ stress regime, pervasive joint orientations relative to bedding, potential for large scale wedges, and ore friability.Three-dimensional modelling results were favourable and indicated that the existing design exceeded stability acceptance criteria. In addition, further optimisation of the slope was possible and would realise an additional 1 Mt of high grade recovery. In order to achieve this, revision of the slope design configuration was required. Work supporting this included assessment of the viability of 90 degree batter face angles and a re-routed haulage design. Batter-berm configurations and placement of wide geotechnical berms were tested for inherent stability and rockfall risk management effectiveness.Overall stability of the revised slope design was confirmed by the Itasca modelling. Some areas of potential local instability were identified and have been addressed by detailed design changes. This project demonstrates the potential value add that can be realised by 3D analysis, when compared with traditional 2D methods. Due to the high value of the STR3 ore as a blending material, this slope is being mined at a relatively high strip-ratio when compared with other RTIO Pilbara pits. This emphasises the potential impact of the protect plan and optimisation outcomes.