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Early Holocene transgressive marine deposits infilling the Pakarae River paleovalley are used to extend the paleoseismic history of the Pakarae River locality, East Coast, North Island, New Zealand, back in time prior to eustatic sea level stabilization at ~7 calibrated (cal) ka B.P. Paleoenvironmental evolution of the Pakarae River paleovalley from 7 to 10 cal ka B.P is reconstructed using sedimentology and biostratigraphy. Two estuarine units display sudden vertical transitions to floodplain sediments implying significant marine regressions and estuary abandonment. These regressions are attributed to coseismic coastal uplift events at ~9000 and ~8500 cal years B.P. A third uplift between 8500 and ~7350 cal years B.P. is inferred from a significant difference between the amount of sediment preserved and the predicted sediment thickness according to the eustatic sea level curve. This study demonstrates the utility of the analysis of transgressive deposits and their paleoenvironmental characteristics for neotectonic investigations on active coasts. doi:10.1029/2006TC002021.

Paleoearthquakes at Earth's surface often generate faults with variable displacement rates over short time intervals (e.g., Keywords: displacement rates, fault interaction, paleoearthquakes, Taupo Rift.

Paleoecological investigations of three Holocene marginal-marine sedimentary sequences provide information on vertical tectonic deformation in a transect across the forearc basin adjacent to the Hikurangi subduction zone, New Zealand. The elevation of maximum postglacial sea level indicators at Te Paeroa Lagoon and Opoho is between 4 and 6 m below present mean sea level, indicating net subsidence since 7200 yr B.P. Opoutama is closer to the Hikurangi Trench and appears to lie near the edge of the zone of subsidence, as evidence for vertical movement there is equivocal. Some of the subsidence at Te Paeroa Lagoon and Opoho is likely to be a result of compaction. However, a component of subsidence probably happened coseismically in two events at ca. 7100 and 5550 yr B.P. Event signatures consist of tsunami deposits overlain by chaotically mixed, reworked sediment that appears to have filled rapidly created accommodation space at marine inlet sites 10 km apart. Large offshore earthquakes are suggested by the coincidence of tsunami inundation with sudden subsidence. Forward elastic-dislocation models indicate that the observed subsidence could be achieved in ~[M.sub.w] 7.9 earthquakes on either the subduction interface or the Lachlan Fault, which would involve synchronous uplift of Mahia Peninsula. Combined rupture of the interface and the Lachlan Fault, either simultaneously in a ~[M.sub.w] 8.1 earthquake, or consecutively, could explain larger amounts (>1.5 m) of coastal subsidence. Keywords: Holocene, Wairoa, Mahia Peninsula, Hawke Bay, Lachlan Fault, accommodation space, earthquakes, microfossils, sea level, subduction zone, subsidence, tsunami.

Glacial landforms at 12 localities in 9 river valleys are offset by the southern end of the onshore Alpine fault. Offsets cluster at ~435, 1240, and 1850 m, consistent with evidence for glacial retreat at 18, 58, and 79 calendar ka. The peak of an offset fluvial aggradation surface is correlated with the Last Glacial Maximum at 22 ka. Displacement rates derived from features aged 18, 22, 58, and 79 cal. ka are 24.2 [+ or -] 2.2, 23.2 [+ or -] 4.9, 21.4 [+ or -] 2.6, and 23.5 [+ or -] 2.7 mm/yr, respectively, with uncertainties at the 95% confidence level. The joint probability, weighted mean, and arithmetic mean of all observations pooled by rank are 23.1 [+ or -] 1.5, 23.2 [+ or -] 1.4, and 23.1 [+ or -] 1.7 mm/yr, respectively. We conclude that the mean surface displacement rate for this section of the Alpine fault is 23.1 mm/yr, with standard error in the range of 0.7-0.9 mm/yr. The reduction in estimated long-term slip rate from 26 [+ or -] 6 mm/yr to 23 [+ or -] 2 mm/yr results in an increase in estimated hazard associated with faulting distributed across the rest of the plate boundary. Model-dependent probabilities of Alpine fault rupture within the next 50 yr are in the range 14%-29%. The 36 [+ or -] 3 mm/yr of total plate motion (NUVEL-1A) is partitioned into 23 [+ or -] 2 mm/yr of Alpine fault dextral strike slip, 12 [+ or -] 4 mm/yr of horizontal motion by clockwise block rotations and oblique dextral-reverse faulting up to 80 km southeast of the Alpine fault, and 5 [+ or -] 3 mm/yr of heave on reverse faults at the peripheries of the plate boundary. Keywords: Alpine fault, tectonics, earthquakes, glacial deposits, plate collision, strike-slip faults.

The Poukawa fault zone, on the North Island of New Zealand within the forearc of the Hikurangi subduction zone, consists of a series of en echelon reverse faults and companion hanging-wall anticlines. The geomorphically expressed length of the fault zone is 34 km. However, on the basis of coseismic deformation associated with an [M.sub.s] 7.8 earthquake in 1931 and the presence of blind faults north of the geomorphically expressed fault zone, it appears that the seismogenic length of the fault zone may be as much as 130 km. On the basis of chronostratigraphic horizons identified in each of three trenches evenly distributed along the exposed fault zone, from which a paleoseismological record for the past [approximately] 25 k.y. can be determined, there is not a characteristic rupture length for earthquakes. Some slip events are confined to the [approximately]10-20-km-long southern part of the fault zone, whereas other slip events may have ruptured the entire 34 km length of the geomorphically expressed fault zone. At least two slip events that occurred in the northern part of the fault zone did not occur in the southern part of the zone. The largest earthquake recorded in the trenches had a maximum reverse slip in excess of 10 m. We infer that this prehistoric earthquake, similar to the 1931 earthquake, entailed slip on faults along the geomorphically expressed fault zone and on blind faults to the north. This prehistoric earthquake may have had a rupture length (surface plus subsurface) in excess of 100 km. Average earthquake repeat times on the fault zone range from 3-7.5 k.y. for the southern and middle part of the zone to 7-12 k.y. for the northern part of the fault zone. Average single-event slip ranges from 3 m to as much as 6 m. Slip was initially accommodated at the surface primarily by folding. With successive slip events, however, coseismic displacements propagated to the surface and surface deformation became increasingly dominated by reverse slip on fault planes. The Poukawa fault zone is part of a foreland-propagating fold and thrust belt in the forearc of the Hikurangi subduction zone. Older, actively eroding hanging-wall anticlines are present to the west of the fault zone toward the volcanic arc, whereas younger folds are developing above blind reverse faults east of the main fault trace. In addition to propagating to the east, the fault zone is propagating northward beneath the Heretaunga Plains. This active propagation testifies to ongoing and evolving contractional forearc deformation in response to oblique plate convergence.

A study of the sedimentary rock types in the former Eketahuna basin in the southern region of the North Island of New Zealand provides insightful information on the structural and tectonic evolution of the inward section of the forearc over the last 10 million years. The forearc region, which was a zone for nonstop marine deposition in the first seven of the last 10 million years, has transformed into the leading edge of the Australian plate.

Mahia Peninsula in eastern North Island, New Zealand, has a sequence of seven marine terraces corresponding to late Pleistocene age. A correlation study with marine terrace sequence of Huon Peninsula, Papua New Guinea, facilitates the determination of ages of these seven terraces. Analysis of 124 ka old shoreline reveals an uplift rate of 1mm\yr at the axis of the anticline and younger marine terraces exhibit rapid uplift. A reverse fault is observed at the eastern margin of the Lachlan anticline and the fault facilitates the growth of anticline and marine terrace deformation.

Uplifted Holocene marine deposits of estuarine and open beach affinities in Mahia Peninsula, Hikurangi, subduction margin in New Zealand facilitates Holocene tectonic characterization. Estuarine deposits that are differentially uplifted belong to the later part of the post glacial transgression. Radiocarbondating of samples from beach deposits reveals five different ages for terraces, with formation of each terrace associated with a large prehistoric earthquake.

An deformation of an exposed forearc in the Pacific-Australian plate convergence zone along the Hikurangi margin, New Zealand is examined via geologic mapping and strain analysis. Partitioning of strain manifested in extension, contraction, and strike-slip domains that lengthen and trend parallel to the margin. Movement oblique to the convergent zone is transferred across the plate boundary. Much of the margin-parallel motion and 6% of the motion perpendicular to the boundary are accounted for by the estimated deformation rates.