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Recent earthquakes involving multiple fault ruptures highlight the need to evaluate complex coastal deformation mechanisms, which are important for understanding plate boundary kinematics and seismic and tsunami hazards. We compare ages and uplift of the youngest Holocene marine terraces at Puatai Beach and Pakarae River mouth (∼10 km apart) in the northern Hikurangi subduction margin to examine whether uplift is the result of subduction earthquakes or upper-plate fault earthquakes. From stepped platform-cliff morphology, we infer uplift during 2–3 earthquakes and calculate an average uplift-per-event of 2.9±0.5 m at Puatai Beach and 2.0±0.5 m at Pakarae River mouth. Radiocarbon ages from the youngest beach deposit shells on each terrace and a tephra coverbed on one terrace constrain the timing of earthquakes to 1770–1710, 1100–910, and 420–250 cal. B.P. at Puatai Beach, and 1490–1290 and 660–530 cal. B.P. at Pakarae River mouth. The ages differ at each site indicating uplift is neither the result of subduction earthquakes nor single upper-plate fault earthquakes. A reinterpretation of new and existing bathymetry and seismic reflection data, combined with dislocation modeling, indicates that near-shore fault segmentation is more complex than previously thought and ruptures likely involve multiple upper-plate faults. Future updates of the New Zealand National Seismic Hazard Model should revise the northern Hikurangi subduction seismic sources so that rupture does not uplift Puatai Beach and Pakarae River mouth and include new near-shore upper-plate faults as multifault sources.

Multiple (>20 \ud >20\ud ) crustal faults ruptured to the ground surface and seafloor in the 14 November 2016 M w \ud Mw\ud 7.8 Kaikōura earthquake, and many have been documented in detail, providing an opportunity to understand the factors controlling multifault ruptures, including the role of the subduction interface. We present a summary of the surface ruptures, as well as previous knowledge including paleoseismic data, and use these data and a 3D geological model to calculate cumulative geological moment magnitudes (M G w \ud MwG\ud ) and seismic moments for comparison with those from geophysical datasets. The earthquake ruptured faults with a wide range of orientations, sense of movement, slip rates, and recurrence intervals, and crossed a tectonic domain boundary, the Hope fault. The maximum net surface displacement was ∼12 m \ud ∼12 m\ud on the Kekerengu and the Papatea faults, and average displacements for the major faults were 0.7–1.5 m south of the Hope fault, and 5.5–6.4 m to the north. M G w \ud MwG\ud using two different methods are M G w \ud MwG\ud 7.7 +0.3 −0.2 \ud 7.7−0.2+0.3\ud and the seismic moment is 33%–67% of geophysical datasets. However, these are minimum values and a best estimate M G w \ud MwG\ud incorporating probable larger slip at depth, a 20 km seismogenic depth, and likely listric geometry is M G w \ud MwG\ud 7.8±0.2 \ud 7.8±0.2\ud , suggests ≤32% \ud ≤32%\ud of the moment may be attributed to slip on the subduction interface and/or a midcrustal detachment. Likely factors contributing to multifault rupture in the Kaikōura earthquake include (1) the presence of the subduction interface, (2) physical linkages between faults, (3) rupture of geologically immature faults in the south, and (4) inherited geological structure. The estimated recurrence interval for the Kaikōura earthquake is ≥5,000–10,000 yrs \ud ≥5,000–10,000 yrs\ud , and so it is a relatively rare event. Nevertheless, these findings support the need for continued advances in seismic hazard modeling to ensure that they incorporate multifault ruptures that cross tectonic domain boundaries.

Paleoseismology has been making an important contribution to understanding the Alpine Fault and the hazard it poses to society. However, evidence of past earthquakes comes from a wide variety of so...

The evolution of the continental intra-arc Taupo Rift in the North Island, New Zealand is rapid, significantly faster than comparative intra-continental rifts such as the African Rifts. Based on our faulting data and published geological, geophysical and borehole data, we show that activity in the ~2 Ma Taupo Rift has rapidly and asymmetrically narrowed via inward and eastward migration of faulting (at rates of ca. 30 km My-1 and 15 km My-1, respectively) and has propagated southwards along its axis ~70 km in 350 kyr. The loci of voluminous volcanic eruptions and active faulting are correlated in time and space, suggesting that a controlling factor in the rapid rift narrowing is the presence of large shallow heterogeneities in the crust, such as large rhyolitic magma bodies generated by subduction processes, which weaken the crust and localize deformation. Eastward migration of faulting also follows the eastward migration of the volcanic arc which may be related to rollback of the Pacific crust slab at the Hikurangi subduction zone. Southward propagation of the rift is linked with southward migration of the Hikurangi plateau/Chatham Rise subduction point and occurs episodically aided by stress changes associated with voluminous local volcanism. The large magma supply during early continental intra-arc rift stages explains faster evolution (from tectonic to magmatic) than intracontinental rifts. However, the fast changes in magma supply from the subduction zone can also lead to evolution reversals (more evolved magmatic stages reverting to less evolved tectonic stages), rift cessation, and thus failed continental break-up.

Coseismic coastal deformation is often used to understand slip on offshore faults in large earthquakes but in the 2016 M W 7.8 Kaikōura earthquake multiple faults ruptured across and sub-parallel to the coastline. Along ∼110 km of coastline, a rich dataset of coastal deformation comprising airborne lidar differencing, field surveying and satellite geodesy reveals highly variable vertical displacements, ranging from −2.5 to 6.5 m. These inform a refined slip model for the Kaikōura earthquake which incorporates changes to the slip on offshore faults and inclusion of an offshore reverse crustal fault that accounts for broad, low-amplitude uplift centered on Kaikōura Peninsula. The exceptional detail afforded by differential lidar and the high variability in coastal deformation combine to form the highest-resolution and most complex record of coseismic coastal deformation yet documented. This should prompt reassessment of coastal paleoseismic records that may not have considered multi-fault ruptures and high complexity deformation fields.

Discovery and investigation of millennial-scale geological records of past large earthquakes improve understanding of earthquake frequency, recurrence behaviour, and likelihood of future rupture of major active faults. Here we present a ∼2000 year-long, seven-event earthquake record from John O'Groats wetland adjacent to the Alpine fault in New Zealand, one of the most active strike-slip faults in the world. We linked this record with the 7000 year-long, 22-event earthquake record from Hokuri Creek (20 km along strike to the north) to refine estimates of earthquake frequency and recurrence behaviour for the South Westland section of the plate boundary fault. Eight cores from John O'Groats wetland revealed a sequence that alternated between organic-dominated and clastic-dominated sediment packages. Transitions from a thick organic unit to a thick clastic unit that were sharp, involved a significant change in depositional environment, and were basin-wide, were interpreted as evidence of past surface-rupturing earthquakes. Radiocarbon dates of short-lived organic fractions either side of these transitions were modelled to provide estimates for earthquake ages. Of the seven events recognised at the John O'Groats site, three post-date the most recent event at Hokuri Creek, two match events at Hokuri Creek, and two events at John O'Groats occurred in a long interval during which the Hokuri Creek site may not have been recording earthquakes clearly. The preferred John O'Groats–Hokuri Creek earthquake record consists of 27 events since ∼6000 BC for which we calculate a mean recurrence interval of 291 ± 23 years , shorter than previously estimated for the South Westland section of the fault and shorter than the current interseismic period. The revised 50-year conditional probability of a surface-rupturing earthquake on this fault section is 29%. The coefficient of variation is estimated at 0.41. We suggest the low recurrence variability is likely to be a feature of other strike-slip plate boundary faults similar to the Alpine fault.

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 a MW6.5 and up to MW7.1 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 res...

The New Zealand Active Faults Database (NZAFD) is a national geospatial database of active faults – including their locations, names and degrees of activity – that have deformed the ground surface of New Zealand within the last 125,000 years. The NZAFD is used for geological research, hazard modelling and infrastructure planning and is an underlying dataset for other nationally significant hazard applications such as the National Seismic Hazard Model. Recent refinements to the data structure have improved the accuracy of active fault locations and characteristics. A subset of active fault information from the NZAFD, generalised for portrayal and use at a scale of 1:250,000 (and referred to as NZAFD250), is freely available online and can be downloaded in several different formats to suit the needs of a range of users including scientists, governmental authorities and the general public. To achieve a uniform spatial scale of 1:250,000 a simplification of detailed fault locational data was required ...

The Kerepehi Fault is an active normal fault with a total onshore length of up to 80 km comprising six geometric/rupture segments, with four more offshore segments to the north. For the last 20 ± 2.5 ka the slip rate has been 0.08–0.4 mm a–1. Average fault rupture recurrence intervals are 5 ka or less on the central segments and 10 ka or more on low slip rate segments to the north and south. Characteristic earthquakes for a single segment rupture range from Mw 5.5 to 7.0, and up to Mw 7.2 or 7.4 in the unlikely event of rupture of all the onshore fault segments. Fault rupture would result in damage to unreinforced masonry buildings, chimneys and parapets in Auckland (45 km nearest distant). Very severe damage to buildings in towns within the Hauraki Plains without specific seismic design (those built before 1960) may pose a significant risk to life and livelihood.

The Alpine fault in south Westland, New Zealand, releases strains of Pacific–Australian relative plate motion in large earthquakes with an average interevent spacing of ∼330 years. A new record of earthquake recurrence has been developed at Hokuri Creek, with evidence for 22 events. The youngest Hokuri Creek earthquake overlaps in time and is believed to be the same as the oldest of another site about 100 km to the northwest near Haast. The combined record spans the last 7900 years and includes 24 events. We study the recurrence rate and conditional probability of ground ruptures from this record using a new likelihood‐based approach for estimation of recurrence model parameters. Paleoseismic parameter estimation includes both dating and natural recurrence uncertainties. Lognormal and Brownian passage time (BPT) models are considered. The likelihood surface has distribution location and width parameters as axes, the mean and standard deviation of the log recurrence for the lognormal, and the mean and coefficient of variation for the BPT. The maximum‐likelihood (ML) point gives the parameters most likely to have given rise to the data. The ML point, 50‐year conditional probabilities of a ground‐rupturing earthquake are 26.8% and 26.1% for the lognormal and BPT models, respectively. Contours of equal likelihood track the parameter pairs that are equally probable to have given rise to the observed data. Conditional probabilities on the lognormal 95% boundary around the ML point range from 18.2% to 35.8%. An empirical distribution model completely based on past recurrence times gives a similar conditional probability of 27.1% (9.6%–50.2%). In contrast, the time‐independent conditional probability estimate of 13.6% (8.8%–19.1%) is about half that of the time‐dependent models. A nonparametric test of earthquake recurrence at Hokuri Creek indicates that time‐dependent recurrence models best represent the southern Alpine fault of the South Island, New Zealand.

Active fault traces are a surface expression of permanent deformation that accommodates the motion within and between adjacent tectonic plates. We present an updated national-scale model for active faulting in New Zealand, summarize the current understanding of fault kinematics in 15 tectonic domains, and undertake some brief kinematic analysis including comparison of fault slip rates with GPS velocities. The model contains 635 simplified faults with tabulated parameters of their attitude (dip and dip-direction) and kinematics (sense of movement and rake of slip vector), net slip rate and a quality code. Fault density and slip rates are, as expected, highest along the central plate boundary zone, but the model is undoubtedly incomplete, particularly in rapidly eroding mountainous areas and submarine areas with limited data. The active fault data presented are of value to a range of kinematic, active fault and seismic hazard studies.

A fundamentally important but typically abbreviated component of seismic‐hazard analysis is the selection of earthquake scaling relationships. These are typically regressions of historical earthquake datasets, in which magnitude is estimated from parameters such as fault rupture length and area. The mix of historical data from different tectonic environments and the different forms of the regression equations can result in large differences in magnitude estimates for a given fault rupture length or area. We compile a worldwide set of regressions and make a first‐order shortlisting of regressions according to their relevance to a range of tectonic regimes (plate tectonic setting and fault slip type) in existence around the world. Regression relevance is based largely on the geographical distribution, age, and quantity/quality of earthquake data used to develop them. Our compilation is limited to regressions of magnitude (or seismic moment) on fault rupture area or length, and our shortlisted regressions show a large magnitude range (up to a full magnitude unit) for a given rupture length or area across the various tectonic regimes. These large differences in magnitude estimates underline the importance of choosing regressions carefully for seismic‐hazard application in different tectonic environments.

The Canterbury earthquake sequence of 2010–2011 is the most significantly impacting event in New Zealand since World War II, consuming >15% of New Zealand's GDP. In Canterbury, geoscience information has contributed significantly to civil defence response management and more recently to the recovery effort coordinated through the Canterbury Earthquake Recovery Authority (CERA) and local authorities in Canterbury. The earthquakes have resulted in major social, community, education and economic disruption, and created considerable uncertainty in relation to the feasibility of land remediation in liquefaction-damaged areas. Analysis of voluminous geoscience, engineering and social science data has and will continue to underpin decisions on the appropriate time to begin infrastructure, residential and commercial rebuild and on whether building codes are appropriate to protect society from rare but potentially catastrophic events.

A team of earthquake geologists, seismologists, and engineering seis- mologists has collectively produced an update of the national probabilistic seismic hazard (PSH) model for New Zealand (National Seismic Hazard Model, or NSHM). The new NSHM supersedes the earlier NSHM published in 2002 and used as the hazard basis for the New Zealand Loadings Standard and numerous other end-user applica- tions. The new NSHM incorporates a fault source model that has been updated with over 200 new onshore and offshore fault sources and utilizes new New Zealand-based and international scaling relationships for the parameterization of the faults. The dis- tributed seismicity model has also been updated to include post-1997 seismicity data, a new seismicity regionalization, and improved methodology for calculation of the seismicity parameters. Probabilistic seismic hazard maps produced from the new NSHM show a similar pattern of hazard to the earlier model at the national scale, but there are some significant reductions and increases in hazard at the regional scale. The national-scale differences between the new and earlier NSHM appear less than those seen between much earlier national models, indicating that some degree of consis- tency has been achieved in the national-scale pattern of hazard estimates, at least for return periods of 475 years and greater. Online Material: Table of fault source parameters for the 2010 national seismic- hazard model.

Strata and fault relationships revealed in five trenches excavated across the recent trace of the Alpine fault at the Haast, Okuru, and Turnbull Rivers, South Westland, New Zealand, record the three most recent surface‐faulting events. Using back‐stripping techniques to remove the three faulting events and the sedimentary units associated with the faulting restores the cross‐sections to gravel‐bed floodplains at the Haast and Okuru Rivers, at about A.D. 750. Horizontal and vertical offsets of stream channels and terrace risers reveal characteristic displacements of about 8–9 m dextral and up to 1 m vertical per event. Cumulative dextral displacement is 25±3 m in the past three events. The most recent surface‐rupture event was probably in A.D. 1717, and the next prior events were about A.D. 1230±50 and about A.D.750±50. The timing of these events is consistent with past large‐great earthquakes on the southern section of the Alpine fault inferred from off‐fault data, but there are fewer events identified in trenches. Our three‐event dataset indicates the average surface‐rupture recurrence interval for the South Westland section of the fault is about 480 years, much longer than the current elapsed time of 295 years. Therefore, the Alpine fault in South Westland may not be close to rupture as is often speculated.

The formation and uplift of Holocene marine terraces along a 160-km-long stretch of the Wairarapa coast in the southern Hikurangi subduction margin, North Island, New Zealand, are interpreted in terms of causative faults and associated large earthquakes during the past circa 7000 cal yr B.P. Distinctive stepped terrace morphology, the clustering of radiocarbon ages on each uplifted terrace, and the historic occurrence of coseismic uplift in other parts of eastern and southern North Island, support the contention that coastal uplift occurred suddenly and repeatedly during large-magnitude earthquakes. The rupture of five west-dipping reverse or reverse-oblique faults within the Australian plate, whose surface traces lie a short distance seaward of the present shoreline, are inferred to be responsible for coastal uplift. Individual structures range in length from 25 to 60 km. These lengths, together with uplift events in the range of 1–4 m, suggest earthquakes in the range of M w 7–7.5. Approximately 20% of the radiocarbon ages are anomalously young for their elevations, but many have ages indistinguishable from accepted ages for terrace uplift. We infer that many of the anomalous ages are from samples deposited by tsunami that occurred in association with offshore fault rupture on adjacent sections of the coast.

The El Salvador earthquake of 13 February 2001 (Mw 6.6) caused tectonic rupture on the El Salvador fault zone (ESFZ). Right-lateral strike-slip surface rupture of the east–west trending fault zone had a maximum surface displacement of 0.60 m. No vertical component was observed. The earthquake resulted in widespread landslides in the epicentral area, where bedrock is composed of volcanic sediments, tephra, and weak ignimbrites. In the aftermath of the earthquake, widespread damage to houses and roads and the hazards posed by landslides captured the attention of responding agencies and scientists, and the presence of surface-fault rupture was overlooked. Additionally, the tectonic context in which the earthquake took place had not been clear until mapping of the ESFZ was completed for the present study.We identified several fault segments, the distribution of surface ruptures, the aftershock pattern, and fault-rupture scaling considerations that indicate the 21-km-long San Vicente segment ruptured in the 2001 event. Static Coulomb stress transfer models for the San Vicente rupture are consistent with both aftershock activity of the 2001 sequence and ongoing background seismicity in the region. At Mw 6.6, the 2001 earthquake was of only moderate magnitude, yet there was significant damage to the country’s infrastructure, including buildings and roads, and numerous deaths and injuries. Thus, earthquake hazard and risk in the vicinity of the ESFZ, which straddles the city of San Salvador with a population of >2 million, is high because even moderate-magnitude events can result in major damage, deaths, and injuries in the region.

Coastlines that trend both parallel and normal to the Hikurangi subduction margin along the Raukumara Peninsula, New Zealand, provide a globally unique situation that enables study of the coastal deformation and its spatial variance across and along the forearc. The data suggest there is margin-parallel zoning of the forearc deformation processes across the Raukumara segment of the Hikurangi margin. On forearc promontories closest to the Hikurangi trench (within 80 km), Holocene marine and fluvial terraces record localised zones of intermittent uplift driven by large coseismic events on landward-dipping nearshore reverse faults. At greater distances from the trench (>100 km), Holocene and Pleistocene coastal stratigraphy and geomorphology suggest that surface uplift occurs by a gradual mechanism: either by frequent small earthquakes or by an aseismic process. In concurrence with geophysical models, we suggest the gradual uplift of this area is most likely driven by the buoyancy of underplated sed...

The Repongaere Fault is one of a series of active normal faults within the Raukumara Peninsula, eastern North Island, New Zealand. These faults appear to form in response to rapid uplift of the Raukumara Range and related extensional strain. However, the activity of these normal faults is poorly constrained. This paper presents new mapping of the active surface trace of the Repongaere Fault, c. 18 km northwest of Gisborne, and the results of two paleoseismic trenches. These results are then used to assess the seismic hazard posed by this fault and impacts on the Waipaoa Sedimentary System in which the fault is situated. Active traces can be mapped for c. 4.5 km, but we infer the surface rupture length to be at least 9 km. Tephras within the trenches constrain the timing of the most recent surface rupture event to have occurred during deposition of the Waimihia Tephra (c. 3400 cal. yr BP), and at least one event in the period c. 13 800–5470 cal. yr BP, with single‐event displacements of ≥0.4–1. 1 ...

The distribution and age of Pleistocene marine terraces fringing the northern Raukumara Peninsula, North Island, New Zealand, is revised. Two terraces, the higher Otamaroa Terrace and the lower Te Papa Terrace, are present from the eastern Bay of Plenty to near east cape. Six optically stimulated luminescence (OSL) ages obtained from the terrace deposits and coverbeds represent the first radiometric ages from these terraces. Loess from the Te Papa Terrace has an age of 62.6 ± 6 ka and the underlying sand has an age of 58.3 ± 4.1 ka. Four OSL ages obtained from sand resting on the bedrock strath of the higher Otamaroa Terrace range from 64.5 ± 4.7 to 79.2 ± 5.5 ka. These OSL ages suggest that the Te Papa Terrace was formed during early Oxygen Isotope Stage (OIS) 3 and the Otamaroa Terrace was formed during OIS 5a. however, global geomorphological and regional loess unit correlations would imply the extensive Otamaroa Terrace correlates with OIS 5e and the loess on the Te Papa Terrace correlates to...

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...

SUMMARY The landmass of New Zealand exists as a consequence of transpressional collision between the Australian and Pacific plates, providing an excellent opportunity to quantify the kinematics of deformation at this type of tectonic boundary. We interpret GPS, geological and seismological data describing the active deformation in the South Island, New Zealand by using an elastic, rotating block approach that automatically balances the Pacific/Australia relative plate motion budget. The data in New Zealand are fit to within uncertainty when inverted simultaneously for angular velocities of rotating tectonic blocks and the degree of coupling on faults bounding the blocks. We find that most of the plate motion budget has been accounted for in previous geological studies, although we suggest that the Porter’s Pass/Amberley fault zone in North Canterbury, and a zone of faults in the foothills of the Southern Alps may have slip rates about twice that of the geological estimates. Up to 5 mm yr −1 of active deformation on faults distributed within the Southern Alps

A suite of seven marine terraces at the Pakarae River mouth, New Zealand, provide evidence for the highest Holocene coastal uplift rates adjacent to the Hikurangi Subduction Zone. New elevation, coverbed stratigraphy, and age data allow for a timely revision of the distribution, nomenclature, and chronology of these terraces. Terrace correlation primarily is based on the elevation of the wave‐cut strath. Terrace preservation either side of the river is more equal than previously proposed. The age of abandonment of each terrace is c. 7 ka (T1), 4.3 ka (T2), 3.5 ka (T3), 2.89 ka (T4), 1.6 ka (T5), 0.91 ka (T6), and

To understand the tectonic evolution of the southern termination of the Taupo Volcanic Zone (TVZ), New Zealand, we compare the late Quaternary structure and kinematics of the southern part of the Taupo Rift or Taupo Fault Belt (Mt Ruapehu Graben) with central parts of the rift (Ngakuru Graben), and with the South Wanganui Basin. We also investigate the differences between displacements of Pliocene and late Quaternary markers within the southern Taupo Rift. Comparison of fault displacement rates derived from displacements of late Quaternary and Pliocene markers yields a preliminary estimate of

Three trenches excavated across the central portion of the right‐lateral strike‐slip Wairau Fault in South Island, New Zealand, exposed a complex set of fault strands that have displaced a sequence of late Holocene alluvial and colluvial deposits. Abundant charcoal fragments provide age control for various stratigraphic horizons dating back to c. 5610 yr ago. Faulting relations from the Wadsworth trench show that the most recent surface rupture event occurred at least 1290 yr and at most 2740 yr ago. Drowned trees in landslide‐dammed Lake Chalice, in combination with charcoal from the base of an unfaulted colluvial wedge at Wadsworth trench, suggest a narrower time bracket for this event of 1811–2301 cal. yr BP The penultimate faulting event occurred between c. 2370 and 3380 yr, and possibly near 2680 ± 60 cal. yr BP, when data from both the Wadsworth and Dillon trenches are combined. Two older events have been recognised from Dillon trench but remain poorly dated. A probable elapsed time of at l...

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.

The Wellington Fault is a major active, right lateral, strike‐slip fault in southern North Island that can be divided into three distinct geometric sections based on changes in neotectonic character and structural complexities. These are, from south to north: the Wellington‐Hutt Valley segment; Tararua section; and Pahiatua section. The Pahiatua section is a 42 km long, straight, NNE‐striking fault section defined between two geometric endpoints near Putara in the south and Woodville. This section has been mapped in detail and exhibits classic strike‐slip tectonic geomorphology and late Quaternary dextral displacements of up to 125 m. Three trenches excavated at sites along the Pahiatua section are used to define the dextral slip rate for this section. At Bennett trench site, a stream is dextrally deflected 50 ± 6 m. Peaty silts underlying “deflected” channel deposits in the trench yield an age of 8390–8700 cal. yr BP, providing a minimum dextral slip rate of 5.1–6.7 mm/yr. At Hughes 1 site, a st...

Eleven sand layers occur within Holocene low- energy estuarine and marginal marine sequences of blue-grey silty clay at two sites on the coastal plain between Wairoa and Mahia Peninsula, northern Hawke's Bay, New Zealand. The sedimentology and fossil assemblages of these layers are consistent with deposition by high-energy influxes to the sites. Three influxes are terrestrial in nature and are thought to represent alluvial flood events. All other sand layers are marine derived and are likely to be the result of storm surges or tsunami. Tsunami inundation is favoured for two sand layers that occur in association with evidence for sudden subsidence at c. 6300 and c. 4800 yr BP. The c. 6300 yr inundation also coincides with previously identified evidence for a tsunami at a site 10 km westwards along the coast. Further investigation is required to distinguish between tsunami and storm surge deposition for the remaining six layers.

The 1929 March 9 Arthur's Pass earthquake of MS7.1 occurred on a newly mapped fault in the Arthur's Pass region, which we name the Poulter Fault. Surface rupture of at least 16 km and possibly as much as 36 km occurred with 4 m of dextral displacement at one site. The extent of fault rupture coincides very closely with a narrow, elongate zone of intense landsliding. A best estimate of the dip‐slip component of faulting is 1–2 m (north side up), making the 1929 rupture a dextral to oblique‐dextral fault displacement, in keeping with earthquake first motion studies. The Poulter Fault is mapped from the South Hurunui River in a WSW direction to Williams Saddle near the confluence of the Mingha and Edwards Rivers, a distance of nearly 50 km. The 1929 earthquake was not on the Kakapo Fault as previously proposed by Yang. No active fault has been found along the line proposed by Yang, and the Kakapo Fault is here redefined as the southern element of a rhomboid fault wedge formed with the Hope Fault bet...

Active faulting in the upper plate of the Hikurangi subduction zone, North Island, New Zealand, represents a significant seismic hazard that is not yet well understood. In northern Wairarapa, the geometry and kinematics of active faults, and the Quaternary and historical surface‐rupture record, have not previously been studied in detail. We present the results of mapping and paleoseismicity studies on faults in the northern Wairarapa region to document the characteristics of active faults and the timing of earthquakes. We focus on evidence for surface rupture in the 1855 Wairarapa (MW 8.2) and 1934 Pahiatua (MW7.4) earthquakes, two of New Zealand's largest historical earthquakes. The Dreyers Rock, Alfredton, Saunders Road, Waitawhiti, and Waipukaka Faults form a northeast‐trending, east‐stepping array of faults. Detailed mapping of offset geomorphic features shows the rupture lengths vary from c. 7 to 20 km and single‐event displacements range from 3 to 7 m, suggesting the faults are capable of g...

We present a new probabilistic seismic hazard analysis (PSHA) for New Zealand. An important feature of the analysis is the application of a new method for the treatment of historical (distributed) seismicity data in PSHA. The PSHA uses the seismicity recorded across and beneath the country to define a three-dimensional grid of a -values (i.e., parameter a of a Gutenberg-Richter distribution log N/yr = a - bM , in which N /yr is the number of earthquakes per year recorded inside each grid cell equal to or greater than magnitude M ); parameter b and the limiting maximum cutoff magnitude of the Gutenberg-Richter distribution are defined from the surrounding region (14 crustal and 23 subcrustal seismotectonic zones are defined for the country) and then smoothed across the boundaries of the zones. The methodology therefore combines the modern method of defining continuous distributions of seismicity parameters (Frankel, 1995; Frankel et al. , 1996) with the traditional method of defining large area sources and the associated seismicity parameters (e.g., Algermissen et al. , 1990). The methodology provides a means of including deep (subduction zone) seismicity in a PSHA, preserves the finer-scale spatial variations of seismicity rates across a region, avoids the undesirable edge effects produced in the traditional method when adjacent area sources enclose areas of significantly different seismicity rates, and also enables parameters most reliably defined at a regional scale (parameter b and maximum cutoff magnitude of a Gutenberg-Richter distribution, and slip type) to be incorporated into the PSHA. The PSHA combines the modeled seismicity data with geological data describing the location and earthquake recurrence behavior of 305 active faults and new attenuation relationships for peak ground acceleration and spectral acceleration developed specifically for New Zealand. Different attenuation expressions are used for crustal and subduction zone earthquakes. The resulting PSH maps for a 150-year return period show the highest hazard to occur in the center and southwest of the country, in the areas of highest historical crustal and deep subduction zone seismicity. In contrast, the longer return-period maps (475 and 1000 year return period) show the highest hazard to occur from the southwest to northeast ends of the country, along the faults that accommodate the majority of the motion between the Pacific and Australian plates. The maps are currently being used to revise New Zealand's building code, which has previously been based on PSHAs that did not explicitly include individual faults as earthquake sources. Manuscript received 10 April 2001.

Estimates of surface rupture displacement and magnitude for crustal earthquakes from the preinstrumental era (pre-1900) tend to be greater than the corresponding estimates derived from modern scaling relations. We investigate this tendency using an expanded and updated version of the earthquake dataset of Wells and Coppersmith (1994) to fit regression relations of moment magnitude on surface rupture length and rupture area and average surface displacement on surface rupture length. Separate relations are fitted to preinstrumental and instrumental data and the results compared to the equivalent relations of Wells and Coppersmith. We find that our relations for instrumental data remove some, but not all, of the differences between the preinstrumental data and the relations of Wells and Coppersmith. We attribute the remaining differences largely to natural censoring of surface displacements less than about 1 m and surface rupture lengths less than about 5 km from the dataset for the preinstrumental era because regressions constructed from similarly censored instrumental data are indistinguishable from the preinstrumental regressions. Since the regressions for our censored instrumental data (i.e., restricted to moderate to large earthquakes) are different from regressions for our complete dataset of instrumental earthquakes and from the regressions of Wells and Coppersmith (both with a larger proportion of small-to-moderate earthquakes), the results may indicate that large earthquakes have different scaling relationships from those of smaller earthquakes.

Remnants of four aggradational terraces in the lower 45 km of the main branch of the Waipaoa River have been correlated with cold/cool climate episodes of the Otiran glaciation. The youngest of the aggradation levels—the Waipaoa‐1 terrace—has the c. 14.7 kaRerewhakaaituTephra as the oldest part of the coverbed sequence, indicating cessation of aggradation about 16 ka BP. This terrace is broadly correlated with Ohakean‐aged terraces in other parts of the North Island. The second most recent episode of aggradation—the Waipaoa‐2 terrace—is slightly older than the c. 28 ka Mangaone Tephra, and is broadly correlated with the Rata terrace. The third most recent aggradation episode— the Waipaoa‐3 terrace—is slightly older than the c. 55–57 ka Rotoehu Tephra (age estimate based on stratigraphic relationships in this study), indicating cessation of aggradation at c. 65 ka BP, and correlative with the Porewa terrace. The fourth, and oldest, aggradation episode we identify in the present landscape—the Waipa...

We examine the drainage system on four anticlinal ridges in Manawatu that affect a mid‐Quaternary (c. 300 000 yr old) marine horizon. The folds are all located above buried, west‐dipping, reverse faults in the basement that are c. 15–20 km long and capable of generating earthquakes of c. MW 6.5–7.0. The drainage systems allow us to distinguish a regional tectonic tilt from the normal plunge of an anticline axis towards its end. We estimate tilt rates of around 4 × 10‐8 rad/yr towards the south averaged over the last c. 300 000 yr. The regional tilting is related to the development and southward migration of the Pliocene‐Pleistocene depocentre in the offshore South Wanganui Basin.

We construct probabilistic seismic hazard (PSH) maps for New Zealand that are based on the distribution and long‐term recurrence behaviour of active faults and the spatial distribution of earthquakes observed in historic time. Slip rate, single‐event displacement, and return time data for 154 active faults (including segments of the Hikurangi and Fiordland subduction zones) are combined with observations of the magnitudes and rupture lengths of large New Zealand earthquakes since 1843 and the instrumental record of seismicity since 1964 to predict the future ground motions that will occur across the country. Maps of the peak ground accelerations and 0.5 s response spectral accelerations expected at 10% probability in 50 yr on “rock” show the highest accelerations (>0.2g and locally over 0.6g) in a belt that extends from the southwestern end of the country to the northeastern end, along the faults that accommodate essentially all of the relative plate motion between the Australian and Pacific plat...

Trenching of 6 of the 10 fault strands that comprise the 5 km long, 1 km wide Rotoitipakau Fault Zone, Taupo Volcanic Zone, New Zealand, shows that surface rupture has occurred at least eight times in the zone during the past 8500 yr. Single‐event displacements on each strand vary from a few decimetres to perhaps more than 2.5 m, and there may have been as much as 4.5–5.0 m of cumulative slip on several strands in a single event. Five airfall tephra whose ages span the past 8500 yr provide time lines within which cumulative slip rate has varied by approximately 10 times: from 1–2.5 mm/yr in the period from the AD 1886Tarawera Tephra to the present, and in the c. 4000 yr period from the 4.8 ka Whakatane Tephra to the 0.65 ka Kaharoa Tephra; to 11 mm/yr in the c. 500 yr period from 0.65 ka to AD 1886. All but one of the fault strands are downthrown to the southeast, suggesting that the fault zone is part of the western margin of the Whakatane Graben. This short fault zone may therefore be a splay o...

The Wellington region is cut by five active right-lateral strike-slip faults : Wairarapa, Wellington, Ohariu, Shepherds Gully/Pukerua, and Wairau faults that have average recurrence intervals of meter-scale surface rupture that range from ∼500 years to 5000 years, and lateral slip rates that range from 1 to 10 mm/yr. Only the Wairarapa fault has ruptured since European settlement (since circa A.D. 1840). Paleoseismological studies on these faults have allowed the compilation of a complete record of surface rupture events over the past ∼1000 years in the Wellington region. Within this time period, there does not appear to be any temporal clustering of surface rupture events on adjacent faults. The M 8 A.D. 1855 Wairarapa earthquake did not trigger rupture on any other fault in the region. The most recent surface-faulting event on the Wellington fault (290-440 cal years B.P.) (cal years are calendar years before A.D. 1950) does not coincide with rupture of any other onland fault, and over 300 years separate the timing of the second most recent rupture on the Wellington fault (660-720 cal years B.P.) and the most recent rupture of the Ohariu fault (1060-1140 cal years B.P.). The most recent rupture of the Shepherds Gully/Pukerua fault is probably older than that of the Ohariu fault. The apparent nonclustering of surface rupture earthquakes in the Wellington region has been documented only for the on-land strike-slip faults. There are other possible seismogenic sources in the region, and thus important issues remain to be addressed regarding the history of large earthquakes in the Wellington region : (1) the seismogenic potential and earthquake recurrence interval of the subduction thrust beneath Wellington is not known ; (2) the timing of rupture events on the offshore portion of the Wairau fault is not known ; and (3) paleoseismic data are not available for the section of the Wellington fault north of the Wellington-Hutt Valley segment. Estimates of earthquake hazard in the Wellington region, for all return times greater than 50 years, that incorporate paleoseismicity data are between one and two Modified Mercalli (MM) intensity units higher than the hazard based solely on the historical seismicity catalog, and the hazard is spatially more variable. Using a deterministic attenuation model, the level of shaking hazard approaches near maximum values within a return time of ∼500 years, largely reflecting the recurrence interval (500-770 years) of surface rupture earthquakes on the Wellington fault. Inclusion of a plausible model for magnitude 8 subduction zone earthquakes does not affect the level of MM intensity in Wellington region at return times greater than 500 years but does make a small contribution to the hazard at return times between 50 and 500 years.

A seismic reflection profile across the c. 25 km long, NNE‐trending Mount Stewart‐Halcombe Anticline in the southeastern Wanganui Basin, along with reinterpretation of its stratigraphy, reveals details of the structure and development of the fold. Two reverse faults (I and II), 1 km apart, bound the eastern side of the anticline and dip at 60— 65° beneath the anticline; a third reverse fault (III) dips 60° to the east towards the adjacent Feilding Anticline. The faults offset basement (Torlesse greywacke), Mangapanian, Nukumaruan, and lower Castlecliffian strata, but do not propagate through upper Castlecliffian ‐ Haweran strata to the surface; this upper part of the sedimentary section is folded but not faulted. Progressive deformation of the sedimentary sequence, as well as differences in sedimentary thickness across the faults, indicates that the Mount Stewart‐Halcombe Anticline has been growing from at least Mangapanian time (c. 3.1 Ma) through to the present. Topographic expression of the an...

Height and age information from Holocene estuarine deposits along the northeastern Marlborough coast provide a database to evaluate coastal vertical tectonics. These data are related to the postglacial marine transgression and coastal geomorphic features formed since the culmination of sea‐level rise. Four tectonic domains are recognised. The Wairau domain is characterised by subsidence at rates over 4 mm/yr. About 60% of this subsidence is tectonic and may be related to Marlborough Sounds subsidence, and 40% is a result of compaction. The Vernon Fault at the south side of the lower Wairau plain separates the Wairau domain from the high‐standing Vernon domain. The Awatere Fault marks the southern boundary between the Vernon domain and the Grassmere domain, which extends from the Awatere River valley to Mussel Point. Slight uplift (c. 1 m in 6500 yr) characterises the Grassmere domain, based on data obtained from Blind River, Lake Grassmere, and, to a lesser extent, from Awatere River fluvial terr...

The accretionary margin of the Hikurangi forearc on the southeast coast of the North Island of New Zealand is part of the leading edge of the Australian plate, which is overriding the obliquely converging Pacific plate. We investigate the last 10 m.y. of deformation history of the innermost (western) quarter of the total width of the forearc through analysis of the sedimentologic and structural evolution of the Eketahuna area on the east coast of the North Island. The Eketahuna area is ideal for such a study because emergence of the margin in the Quaternary has exposed a complete late Neogene rock record. This record has allowed us to chronicle the strain history. From 10 Ma to about 2.5 Ma this forearc region was the locus of subsidence and marine deposition. In the latest Pliocene this part of the margin began to shorten through folding and reverse faulting, bringing an end to basin filling. The period of shortening was brief, and by the late Pleistocene, reverse faulting had ceased and was immediately succeeded by dextral strike-slip faulting, in some cases along the same faults. Presently, the dominant strain regime in the inner quarter of the forearc is strike-slip faulting. This structural history illustrates that, over time, the pattern of strain partitioning has changed in the Hikurangi forearc. The switch from crustal shortening to dextral shear along the major faults in this area in the last 1 m.y. may be a response to more than 10° of clockwise rotation in the southern Hikurangi forearc in Pliocene and Pleistocene time. This rotation is a consequence of the fact that the accretionary margin is undergoing continuous deformation between the obliquely converging Australian and Pacific plates in this area at the southernmost end of the Kermadec-Hikurangi subduction system. The inboard portion of this young accretionary margin is exceptionally well exposed today, probably in part because of the late Neogene subduction of relatively thick, buoyant crust of the Hikurangi-Chatham plateau.

A flight of coral terraces, up to ca. 1, 000 m above sea level, is well preserved on the northern coast of the Huon Peninsula, Papua New Guinea, and records the sea level and tectonic history since ca. 300 ka. The region is located near the boundary between the Western Pacific and Australian plates. The uplift rate since the last interglacial maximum (oxygen isotope stage 5e) ranges from 0.7 m/ka at the northwest end of the coast, and up to 3.5 m/ka towards the southeast end. Late Quaternary paleoseismicity is estimated from subdivided Holocene and late Pleistocene terraces, each of which records meter-scale coseismic uplift events.The study area covers about 40 km of coast. Holocene coral terraces, up to 25 m above sea level, are divided into seven levels at maximum, four to five at most sites. The highest Holocene terrace is a reef crest representing former sea level of the culmination of the sea level rise at ca. 6-6.6 ka BP. The lower terraces are regressive terraces, which record successive intermittent uplift events, probably caused by great earthquakes. Timing of the Holocene uplift events is ca. 2.5, 3.8, 4.4-5.1, and 5.4 ka BP at Kwambu-Kilasairo area on the northwestern coast, and at ca. 0.8, 1.4, 1.8, 2.5, 3.9 and 5.4 ka BP at Kanomi-Nanda area to Hubegong on the central and southern coast. Difference in the timing of the uplift events implies that there are at least two tectonic suregions on this coast.Similar small regressive terraces are also recognized from the detailed profiles of late Pleistocene terraces. For example, in the central and southern part of the study area, 15-7 extra steps occur between transgressive terrace IIIa (ca. 52 ka) and terrace II (ca. 38 ka). Thus, we infer that repeated meter-scale uplift events have occurred at least since ca. 52 ka. The apparent interval of uplift events, about 1-1.5 ka, resembles to that for Holocene.Such a meter-scale uplift with ka-scale recurrence intervals records a different earthquake deformation cycle from the centimeter-scale uplift associated with the 1992 May earthquake (M= 7.2 : Pandolfi et al., 1994). Such a small event with shorter recurrence interval is apparently not expressed geomorphologically as in the form of regressive terrace.

This paper summarises the tectonic setting and seismicity of the Huon Peninsula, based on recently published papers. Some characteristic aspects of tectonic geomorphology are also briefly reviewed.The Huon Peninsula on the northeastern Papua New Guinea, located on ca. 6° S, is a suitable place for Quaternary sea level study, because coral reef terraces as an indicator of former sea level position are well preserved as separate terraces on land, due to strong uplift on the collision zone between the Australian and Pacific plate. The plate boundary is traced on land as Ramu-Malkahm Fault Zone. The formation of the Huon-Finisterre Range is a result of the collision of these two plates during the Quaternary. Fault plane solution for the major shallow earthquakes indicates that many of them are by reverse faults, strike of which is perpendicular to the fault zone. Thus, it can be said that the north-south oriented compression has been dominated at this fault zone.A flight of coral terraces, up to ca. 1, 000 m in altitude, fringes the northeastern coast of this tectonically active Huon Peninsula. U-series dates have been obtained from the terraces younger than Terrace VII, correlated with isotope stage 5e of the last interglacial maximum. Terrace height shows the northwestward downtilting, with some irregularity, from the maximum uplift rate of 3.5 m/ka. The uplift rate since the isotope stage 5e agrees with that for the Holocene, implying that the same pattern of tectonic uplift with the uniform rate has continued during the late Quaternary.Rapid uplift of this area is a result of repeated coseismic uplift which has an meter-scale uplift and ka-scale interval. Evidence of the coseismic uplift is obtained from both Holocene terraces and late Pleistocene terraces. Some of large landslides disrupting coral terraces are also originated coseismically. Coseismic process is an important tectonic factor for the formation and emergence and also for the destruction of coral terraces. These topics, related to paleoseismicity, are discussed in detail elsewhere in another papers in this special issue.Some landforms, related to active tectonics, such as active faults, uplifted alluvial deltas, and stream system, are also briefly discussed in the paper.

A sequence of seven marine terraces of late Pleistocene age constitutes approximately 40% of the area of Mahia Peninsula in eastern North Island. The peninsula is one of the closest land areas to the Hikurangi Trough (approximately 80 km further east), where the Pacific plate is being subducted beneath the Australian plate. Terrace ages of 40, 59, 81, 106, 124, 176, and 212 ka are assigned by correlation with the marine terrace sequence of Huon Peninsula, Papua New Guinea. Paleontological data and amino acid dating of marine components of the 124 ka terrace at Mahia Peninsula provide a basis for correlation to the Huon Peninsula sequence. Loess and tephra stratigraphy constrain the ages of older and younger terraces. The marine terrace sequence is tilted to the WNW on the flank of the NNE trending Lachlan anticline. Uplift of at least 130 m of the circa 124-kyr-old shoreline indicates uplift rates of at least 1 mm/yr at the axis of the anticline. Younger marine terraces have been uplifted more rapidly (about 3 mm/yr), and there is a progressive increase in rate to the youngest Holocene shoreline. Structural contours normalized to the circa 124 ka terrace illustrate the tilt on the flank of the Lachlan anticline and on a secondary structure, the Aurora Point fold. Seismic profiling has confirmed the presence of a reverse fault (the Lachlan fault) at the eastern margin of the Lachlan anticline. The Lachlan fault is inferred to be responsible for growth of the anticline and deformation of the marine terraces. The relationship of the reverse fault to the subduction thrust, which separates the two crustal plates at about 20 km depth below Mahia Peninsula and dips about 6°–12° to the NW, is uncertain. However, the late Pleistocene and Holocene growth of the Lachlan anticline indicates substantial coupling across the plate interface, deforming the inner part of the frontal wedge of the Australian plate.

Mahia Peninsula is a prominent coastal landmark in eastern North Island and is the closest point of land in the North Island to the Hikurangi Trough, where the Pacific plate plunges beneath the subduction complex at the eastern margin of the Australian plate. Uplifted Holocene marine deposits of both estuarine and open beach affinities are found in many parts of the peninsula and provide the basis for Holocene tectonic characterization. Estuarine deposits record the later part of the postglacial transgression that culminated about 6500 years B.P. in New Zealand. The deposits have been differentially uplifted since that time at a rate of 2.5 ± 0.3 mm/yr in the central north coast area, decreasing to 0.7 ± 0.2 mm/yr about 6 km to the west. The coastal plain is characterised in many places by a stepped sequence of emergent shore platforms overlain by fossiliferous beach deposits. Extensive radiocarbon dating of samples from beach deposits shows that terraces in widespread parts of the peninsula are of five distinct ages. Each of the terraces is inferred to have formed in conjunction with a large prehistoric earthquake because of the stepped terrace morphology, clustering of ages on each terrace, differential uplift of terraces across the peninsula, and historic coseismic uplift events in this tectonic setting. Paleoseismic events of Mw 7.5–8.0 are estimated to have occurred approximately 250, ∼1600, ∼1900, ∼3500, and ∼4500 years B.P. Uplift distribution of the Holocene and late Pleistocene marine terraces shows that the peninsula lies on the west (gentle) flank of the active Lachlan anticline, which is cored by a major west dipping reverse fault (the Lachlan fault). Holocene active deformation at Mahia Peninsula and other coastal areas of eastern North Island is a continuation of structures developed in Pleistocene time in the landward part of the subduction complex adjacent to the Hikurangi subduction zone.

The Wellington Fault is one of the major active right‐lateral strike‐slip faults of the southern North Island and represents a significant seismic hazard to the greater Wellington region. Trench excavations across the fault in the Long Gully/Karori Reservoir area and near Kaitoke, along with Quaternary stratigraphic and soil studies at Te Mania, indicate that the most recent surface rupture event along the southern portion of the Wellington Fault was 300–450 cal B .P. (calendar years before A.D. 1950) and the next oldest event was 670–830 cal B.P. The elapsed time between these two events is 220–530 years. Based on the previously reported 6.0–7.6 mm/yr, long‐term (c. 140 ka), average, horizontal slip rate calculated at Emerald Hill, and the 3.2–4.7 m single‐event offsets (the five most recent events) measured at Te Marua, the average recurrence interval for this portion of the Wellington Fault is 420–780 years. At the Long Gully trench site, two stream channels are laterally displaced by c. 50 m....

Rotoehu Ash, a widespread tephra marker in central and eastern North Island, occurs within terrestrial cover deposits overlying some shore platforms at Mahia Peninsula. Several loess units, tephra, and paleosols overlie shore platforms and provide age and paleoclimatic information for the period subsequent to shore platform formation. These data, along with faunal and floral samples, enable the terrace sequence to be correlated with the well‐dated, late Quaternary coral reef sequence at Huon Peninsula, Papua New Guinea. The youngest shore platform at Mahia Peninsula on which the Rotoehu Ash occurs is correlated to the 59 ka B.P. reef crest; it does not occur on a shore platform correlated to the c. 40 ka B.P. reef crest at Huon Peninsula Evaluation of the stratigraphic sequence on the 59 ka B.P. Auroa 2 shore platform results in an age estimate of the Rotoehu Ash of 52 ± 7 ka B.P. Previous radiocarbon dates indicating an age of c. 42 ka B.P. are considered to be minimum values. Climato‐stratigrap...

The Hikurangi subduction margin, New Zealand, has not experienced any significant (>Mw 7.2) subduction interface earthquakes since historical records began ∼170 years ago. Geological data in parts of the North Island provide evidence for possible prehistoric great subduction earthquakes. Determining the seismogenic potential of the subduction interface, and possible resulting tsunami, is critical for estimating seismic hazard in the North Island of New Zealand. Despite the lack of confirmed historical interface events, recent geodetic and seismological results reveal that a large area of the interface is interseismically coupled, along which stress could be released in great earthquakes. We review existing geophysical and geological data in order to characterize the seismogenic zone of the Hikurangi subduction interface. Deep interseismic coupling of the southern portion of the Hikurangi interface is well defined by interpretation of GPS velocities, the locations of slow slip events, and the hypocenters of moderate to large historical earthquakes. Interseismic coupling is shallower on the northern and central portion of the Hikurangi subduction thrust. The spatial extent of the likely seismogenic zone at the Hikurangi margin cannot be easily explained by one or two simple parameters. Instead, a complex interplay between upper and lower plate structure, subducting sediment, thermal effects, regional tectonic stress regime, and fluid pressures probably controls the extent of the subduction thrust's seismogenic zone.

The Wellington Fault is one of the major active dextral strike-slip faults of southern North Island. Quaternary stratigraphic studies and fault mapping along the southern part of the fault in Upper Hutt have provided some data on slip rates and recurrence intervals. Horizontal offsets of terrace risers and channels on terrace surfaces range from 3.7 m to 900 m. Increasing numbers of loess units, separated by paleosols, on successively older fluvial terraces in the Upper Hutt and Kaitoke Basins, provide a means of dating the terraces and, together with displacement measurements, a means of estimating horizontal slip rates on the Wellington Fault. At Emerald Hill, a terrace with an estimated age of 14 ± 4ka is dextrally offset by 104± 10m(after correcting for tread width differences of the terrace on either side of the fault). An older terrace estimated to be about 70 ± 5 ka is offset by 437 ± 20 m, and a 940 ± 40 m offset is associated with a terrace about 140 ± 10 ka. These displacement/age pairs...