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At the eastern boundary of the south Taupo Rift, the NE-striking, rift-bounding Rangipo and the ENE-striking Wahianoa active normal faults intersect. We investigate their intersection at the Upper Waikato Stream to understand the kinematics of a rift termination in an active volcanic area. The Upper Waikato Stream Fault is a previously unrecognised seismogenic source also at the eastern boundary, capable of producing aMW6.5 and up toMW7.1 earthquake if it ruptures in conjunction with the Rangipo or Wahianoa faults. We found a minimum of 12 surface-rupturing earthquakes in the last 45.16 ka on the Upper Waikato Stream Fault (mean slip-rate c. 0.5 mm/yr), and a minimum of nine surface-rupturing earthquakes in the last 133 ka on the Wahianoa Fault (mean slip-rate c. 0.2 mm/yr). Periods of highest slip-rate on these faults may coincide in time with Taupo, Ruapehu or Tongariro eruptions, but, despite their intersection, movement was not coincident across all faults. The Upper Waikato Stream Fault responded to a major Taupo Volcano eruption, the Wahianoa to a major eruptive sequence from Mt Tongariro and the Rangipo to major explosive events from Mt Ruapehu. [ABSTRACT FROM PUBLISHER]

Six trenches and additional exposures have been investigated along a 23 km length of the Pahiatua section of the Wellington Fault. The sites show a consistent fault rupture record for the last four surface-faulting events along the Pahiatua section. This multi-site record of events, supported by 28 radiocarbon ages that span the last c. 4500 yr, is the most complete paleoseismic record for the Wellington Fault. From southwest to northeast, the trenches are called death-1 and -2, Hughes-2 and -1, and ebbett-2 and -1, named after local farmers. Additional data come from an exposure at the Army Depot northeast of Ebbett-1 and a stream cutting near the Death-1 trench. Earthquake events are recognised on the basis of upward terminations of faults and stratigraphic evidence (unconformities; scarp-derived colluvial deposits; "co-seismically" generated, organic, poorly sorted units; and subsequent scarp-ponded units). On this basis, evidence for the most recent surface-faulting event is recognised at all sites (i.e., between death-1 and the army depot site) and has a timing of ad 1670-1800 (150-280 cal. yr BP). The penultimate faulting event has been recognised at all six trenches and occurred between ad 690 and 1170 (780-1260 cal. yr BP). Clear evidence, and datable material associated with events III and IV, is observed only in the older records of the Ebbett-1 and Hughes trenches. Event iii is bracketed by faulting and two ages on co-seismic deposits to the interval ad 65 to 400 BC (1885-2350 cal. yr BP). Event IV is bracketed by three key ages in the Hughes-1 trench to the interval 1600-2140 BC (3550-4090 cal. yr BP). The trench-derived recurrence interval based on these four events is c. 1200 ± 110 yr, which is consistent with, though longer than, an estimate of the recurrence interval based on slip rate (5.1-6.2 mm/yr) and single-event displacement (4.5 ± 1 m), which gave a range of 820 ± 260 yr. When the current paleoseismic data for the Wellington Fault are considered together, they suggest that: (1) the last four large earthquakes along the Pahiatua section have involved rupture of the entire section; (2) these events broadly correlate with other dated paleoearthquake events along the Wellington-Hutt Valley segment and Tararua section of the fault, and the southern end of the Mohaka Fault; (3) the most recent faulting event along the Pahiatua section is somewhat younger than for the Wellington-Hutt Valley segment or Tararua section; and (4) either single or dual segment/section rupture scenarios existed along these four fault sections. [ABSTRACT FROM AUTHOR]

Late Quaternary structure and kinematics at the southern termination of the Taupo Rift are investigated by means of active fault mapping and estimates of fault displacement and extension rates. Active faults in the southern Taupo Rift are normal in sense and include three major structures: the NNE-trending Mt Ruapehu Graben; the E-W to ESE-WNW-trending Ohakune-Raetihi fault set; and the NE-trending Karioi fault set. Displacements of young geomorphic features, fault plane exposures in roadcuts, and trenches across faults show that all faults are active contemporaneously. The Mt Ruapehu Graben is the southern extension of the modern (i.e., <26 ka) Taupo Rift (or Taupo Fault Belt, TFB), and has developed as a result of backarc extension related to the Hikurangi subduction margin. Geologic extension rate for the Mt Ruapehu Graben is estimated here at 2.3 ± 1.2 mm/yr. The other two structures strike almost perpendicular to the Taupo Rift terminating the Mt Ruapehu Graben to the south. The co-existence of three normal fault sets in mutual crosscutting relations and with no significant strike-slip on any of them may be related to local reorientation of the minimum principal stress axis (σ3) or to a stress tensor where |σ3| ≈ |σ2|. Complicated strains at the southern termination of the Taupo Rift are related to block rotations in the Hikurangi subduction margin. [ABSTRACT FROM AUTHOR]

A sedimentary sequence that was highly sensitive to fault rupture-driven changes in water level and sediment supply has been used to extract a continuous record of 22 large earthquakes on the Alpine fault, the fastest-slipping fault in New Zealand. At Hokuri Creek, in South Westland, an 18 m thickness of Holocene sediments accumulated against the Alpine fault scarp from ca. A.D. 800 to 6000 B.C. We used geomorphological mapping, sedimentology, and paleoenvironmental reconstruction to investigate the relationship between these sediments and Alpine fault rupture. We found that repeated fault rupture is the most convincing mechanism for explaining all the features of the alternating peat and silt sedimentary sequence. Climate has contributed to sedimentation but is unlikely to be the driver of these cyclical changes in sediment type and paleoenvironment. Other nontectonic causes for the sedimentary alternations do not produce the incremental increase in basin accommodation space necessary to maintain the shallow-water environment for 6800 yr. Our detailed documentation of this near-fault sedimentary basin sequence highlights the advantages of extracting paleoearthquake records from such sites--the continuity of sedimentation, abundance of dateable material, and pristine preservation of older events. [ABSTRACT FROM AUTHOR]