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Minor changes in geometry along the length of mature strike-slip faults may act as conditional barriers to earthquake rupture, terminating some and allowing others to pass. This hypothesis remains largely untested because palaeoearthquake data that constrain spatial and temporal patterns of fault rupture are generally imprecise. Here we develop palaeoearthquake event data that encompass the last 20 major-to-great earthquakes along approximately 320 km of the Alpine Fault in New Zealand with sufficient temporal resolution and spatial coverage to reveal along-strike patterns of rupture extent. The palaeoearthquake record shows that earthquake terminations tend to cluster in time near minor along-strike changes in geometry. These terminations limit the length to which rupture can grow and produce two modes of earthquake behaviour characterized by phases of major (Mw 7–8) and great (Mw > 8) earthquakes. Physics-based simulations of seismic cycles closely resemble our observations when parameterized with realistic fault geometry. Switching between the rupture modes emerges due to heterogeneous stress states that evolve over multiple seismic cycles in response to along-strike differences in geometry. These geometric complexities exert a first-order control on rupture behaviour that is not currently accounted for in fault-source models for seismic hazard. The rupture mode between major and great earthquakes is controlled by transform fault geometry, according to simulations of a reconstructed record of 20 palaeoearthquakes along the Alpine Fault, New Zealand.

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.

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...

At Table Cape, Mahia Peninsula, North Island, New Zealand, four marine terraces have been uplifted coseismically during the past 3500 years. Detailed facies assessment of the terrace coverbed sequence coupled with identification of modern analogues on the active shore platform were used to infer the process of marine terrace formation and to estimate the timing and amount of past uplift events (earthquakes). The modern platform can be subdivided into seven depositional zones: subtidal, outer platform, intertidal sand pockets, inner platform, high-tide, mid-storm, and storm beach. Terrace coverbeds were characterised from two trenches excavated across the full width of the uplifted terrace sequence. Off-lapping packages of high tidal, mid-storm, and storm beach sediments were most common. Outer platform sediments occurred only rarely near the base of some uplifted shore platforms. Overlying the marine sediments were near-horizontal terrestrial deposits of airfall tephra (on the two highest terraces), subsoil, topsoil, rare wedges of colluvial sediment (slopewash) shed from terrace risers, and an anomalous deposit possibly emplaced by a tsunami. Fifty-one radiocarbon ages, obtained from molluscs in the marine coverbeds, showed a general pattern of seaward-younging across the coastal plain and across each terrace and a less pronounced pattern of decreasing age upward in each coverbed sequence. The distinctive stepped geomorphology of the terraces, the facies and age structure of the terrace deposits and historical earthquake causation of similar terraces elsewhere in New Zealand provided the data to invoke an earthquake-driven model for terrace formation. Marine terrace development following an uplift event involved rapid cutting of a new intertidal shore platform and generally regressive deposition of high-tide to storm beach deposits. Following further uplift, the platform became a geomorphic terrace (above marine influence) and was then mantled by terrestrial sediments. On the two highest terraces at Table Cape, airfall tephras mantling the marine coverbeds provided a minimum age for terrace uplift. The youngest radiocarbon ages from high-tide deposits high in the stratigraphy and near the seaward edge of each terrace provided the best estimates for the timing of uplift. Based on the new radiocarbon ages and the constraining airfall tephra ages, we revised the earthquake ages to 3530–3350, 1810–1730, 1560–1300 and 300–100 cal. YBP. Associated best estimates of the coseismic uplift amounts were 2.1, 1.4, 1.8, and 3.1 m respectively, once we accounted for eustatic sea level changes through the late Holocene.

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.

The Global Alliance of Disaster Research Institutes held its 3rd Global Summit of Research Institutes for Disaster Risk Reduction at the Disaster Prevention Research Institute, Kyoto University, Japan, 19–21 March, 2017. The Global Alliance seeks to contribute to enhancing disaster risk reduction (DRR) and disaster resilience through the collaboration of research organizations around the world. The summit aim was to expand the platform for bridging science and policy making by evaluating the evidence base needed to meet the expected outcomes and actions of the Sendai Framework for Disaster Risk Reduction 2015–2030 and its Science and Technology Roadmap. The summit reflected the international nature of collaborative research and action. A pre-conference questionnaire filled out by Global Alliance members identified 323 research projects that are indicative of current research. These were categorized to support seven parallel discussion sessions related to the Sendai Framework priorities for action. Four discussion sessions focused on research that aims to deepen the understanding of disaster risks. Three cross-cutting sessions focused on research that is aimed at the priorities for action on governance, resilience, and recovery. Discussion summaries were presented in plenary sessions in support of outcomes for widely enhancing the science and policy of DRR.

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 Global Earthquake Model (GEM) aims to develop uniform, openly available, standards, datasets and tools for worldwide seismic risk assessment through global collaboration, transparent communication and adapting state-of-the-art science. GEM Faulted Earth (GFE) is one of GEM’s global hazard module projects. This paper describes GFE’s development of a modern neotectonic fault database and a unique graphical interface for the compilation of new fault data. A key design principle is that of an electronic field notebook for capturing observations a geologist would make about a fault. The database is designed to accommodate abundant as well as sparse fault observations. It features two layers, one for capturing neotectonic faults and fold observations, and the other to calculate potential earthquake fault sources from the observations. In order to test the flexibility of the database structure and to start a global compilation, five preexisting databases have been uploaded to the first layer and two to the second. In addition, the GFE project has characterised the world’s approximately 55,000 km of subduction interfaces in a globally consistent manner as a basis for generating earthquake event sets for inclusion in earthquake hazard and risk modelling. Following the subduction interface fault schema and including the trace attributes of the GFE database schema, the 2500-km-long frontal thrust fault system of the Himalaya has also been characterised. We propose the database structure to be used widely, so that neotectonic fault data can make a more complete and beneficial contribution to seismic hazard and risk characterisation globally.

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.

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.

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.

The Sedimentary Life of Earthquakes Estimating the hazards associated with possible large earthquakes depends largely on evidence of prior seismic activity. The relatively new global seismic networks installed to monitor earthquakes, however, have only captured the very recent history of fault zones that can remain active for thousands of years. To understand the recurrence of large earthquakes along the Alpine Fault in New Zealand, Berryman et al. (p. 1690 ) looked to the sediments near an old creek for evidence of surface ruptures and vertical offset. Along this fault segment, 24 large earthquakes seem to have occurred over the last 6000 years, resulting in a recurrence interval of ∼329 years. The activity is more regular than other similar strike-slip faults, such as the San Andreas Fault in California.

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.

From a data set of 50 published and new fault exposures, we establish a 26,000 year record of associations between the timing of fault rupture in two sectors of the Taupo rift, New Zealand, and deposition on the fault scarps of rhyolitic fall tephra from the adjacent Okataina volcanic center. We also investigate processes that could be responsible for the time associations. From 40 high-resolution couplets of fault rupture and volcanic eruption (located up to 30 km distant), we show that 30% of the fault ruptures occurred when the volcano was erupting, whereas in 70% of the cases volcanism and faulting were independent. Other geological and geophysical information indicates that faulting in the Taupo rift is essentially tectonic and, thus, most of the cases with time association between fault rupture and volcanic eruption found in the fault exposures in this study are interpreted to be a manifestation of stress transfer between faults and magmatic storage zones beneath the volcanic center. In a few cases close (

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.

Fault interactions are an essential feature of all fault systems on timescales of individual earthquakes to millions of years. We examine the role of these interactions in the development of an array of normal faults within the active Taupo Rift, New Zealand. Stratigraphic horizons (0–26 ka) exposed in 30 trenches and laterally extensive topographic surfaces (∼18–340 ka) record displacements during surface-rupturing earthquakes over time intervals of up to 100’s of thousands of years. Complementary changes in displacements, displacement rates and earthquake histories between faults are observed for along-strike displacement profiles and at points on fault traces. Variations of displacement are attributed mainly to fault interactions, and decrease with the aggregation of displacements on progressively more faults and over longer time intervals. Rift-wide displacement rates are, for example, near-constant over timescales of

Determining the spatial and temporal deliveries of sediment from the Waipaoa River catchment in the post-glacial period is a major goal of integrated source-to-sink landscape evolution studies in the region. In a 2.2 km long section of the Waihuka tributary (217 km 2 ) of the Waipaoa River (2150 km 2 ) in eastern North Island, New Zealand, a sequence of at least ten fluvial terraces and abandoned meanders up to 45 m above the present river records rates and times of post-glacial downcutting. Dateable organic and tephra horizons in the terrace and meander infill stratigraphy indicate that downcutting at this location on the Waihuka tributary was dominated by a short-lived event in the early Holocene from 10–8 ka BP, when as much as half of the downcutting was accomplished in only 10–15% of post-glacial time. The large downcutting event is interpreted to record the passing of a succession of major knickpoints or a knickzone through this tributary. The initiation of knickpoint retreat in the catchment was primarily a consequence of reduction in sediment supply at the end of MIS 2. Based on the timing of rapid downcutting in the Waipaoa River mainstem, we estimate that the rate of knickpoint retreat along the Waihuka tributary was about 2 km/kyr. In the period before and after rapid downcutting in the Waihuka tributary, modest incision rates, averaging 1–2 mm/yr, probably represent the regional tectonic uplift rate.

One of the major environmental controls on sedimentary systems is tectonics, and thus in order to make quantitative explanations and predictions of the behaviour of sedimentary systems, it is important to quantify tectonic rates and mechanisms. In this study we show how a combined Holocene fluvial and marine terrace dataset can be used to place constraints on coastal uplift mechanisms at Pakarae River mouth, to the east of the Waipaoa sedimentary system. Mapping and surveying of fluvial terraces shows that the terraces can be divided into three sets, (i) PgT, a fill terrace formed during post-glacial sea level rise (~ 10000–7000 cal. yr BP), (ii) a sequence of post-7000 cal. yr BP degradation terraces, and (iii) historical (post ~ AD 1880) flood terraces. A conceptual model of terrace evolution proposes that coseismic uplift has resulted in the observed back-tilting, downstream divergence, and successive abandonment of tectonic terraces. Coastal uplift mechanisms are then examined by comparing the fluvial and marine terrace uplift distribution and the uplift-per-event from the marine terraces with those predicted by forward elastic dislocation models. The models agree with the interpretation that the terrace uplift can be explained by coseismic slip on a steeply west-dipping reverse fault located close to the shore, possibly in combination with rupture of the Hikurangi Margin subduction interface 10–24 km below. This study also provides insights into the tectonic drivers and impacts on the adjacent Waipaoa sedimentary system including: the possible role of subduction earthquakes, growth of structures on the shelf and upper slope, and the role that the interplay between sea level and tectonic controls has on sediment dispersal.

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...

The coastal geomorphology of the northeastern Raukumara Peninsula, New Zealand, is examined with the aim of determining the mechanisms of Holocene coastal uplift. Elevation and coverbed stratigraphic data from previously interpreted coseismic marine terraces at Horoera and Waipapa indicate that, despite the surface morphology, there is no evidence that these terraces are of marine or coseismic origin. Early Holocene transgressive marine deposits at Hicks Bay indicate significant differences between the thickness of preserved intertidal infill sediments and the amount of space created by eustatic sea level rise, therefore uplift did occur during early Holocene evolution of the estuary. The palaeoecology and stratigraphy of the sequence shows no evidence of sudden land elevation changes. Beach ridge sequences at Te Araroa slope gradually toward the present day coast with no evidence of coseismic steps. The evolution of the beach ridges was probably controlled by sediment supply in the context of a background continuous uplift rate. No individual dataset uniquely resolves the uplift mechanism. However, from the integration of all evidence we conclude that Holocene coastal uplift of this region has been driven by a gradual, aseismic mechanism. An important implication of this is that tectonic uplift mechanisms do vary along the East Coast of the North Island. This contrasts with conclusions of previous studies, which have inferred Holocene coastal uplift along the length of the margin was achieved by coseismic events. This is the first global example of aseismic processes accommodating uplift at rates of >1 mm yr−1 adjacent to a subduction zone and it provides a valuable comparison to subduction zones dominated by great earthquakes.

Paleoenvironmental reconstructions of three coastal waterbodies in Wellington, New Zealand, reveal that sites were isolated from the sea within the last 7500 years through coseismic uplift and barrier growth. Evidence for coseismic uplift consists of distinct transitions in diatom assemblages representing large changes in relative sea-level or water-table level, commonly in association with sedimentological evidence for catchment disturbance or marine influx. Transitions are abrupt, laterally extensive and synchronous within each waterbody. Amount of change across transition horizons is assessed using quantitative estimates of paleosalinity and waterbody type as proxies for relative sea-level change. Seven transitions involve large paleoenvironmental changes and provide evidence for earthquakes occurring at approximately 5100, 3200 (recorded at two sites), 2300 (recorded at two sites), 1000 cal years BP and 1855 AD. Five other transitions involve smaller paleoenvironmental changes and are considered to be consistent with effects of earthquakes but do not provide independent evidence for earthquake occurrence. These smaller transitions occur at approximately 6800, 3600, 2200, 1000 (coincident with a large transition) and 500 cal years BP. The data refine ages and provide information about the extent and effects of past large earthquakes in the region. These are the first paleoecologically derived earthquake signatures for Wellington and they contribute to the sparse collection worldwide of off-fault sedimentary earthquake records for predominantly strike-slip faults.

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

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 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 w 8.1 earthquake, or consecutively, could explain larger amounts (>1.5 m) of coastal subsidence.

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...

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 ± 2.2, 23.2 ± 4.9, 21.4 ± 2.6, and 23.5 ± 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 ± 1.5, 23.2 ± 1.4, and 23.1 ± 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 ± 6 mm/yr to 23 ± 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 ± 3 mm/yr of total plate motion (NUVEL-1A) is partitioned into 23 ± 2 mm/yr of Alpine fault dextral strike slip, 12 ± 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 ± 3 mm/yr of heave on reverse faults at the peripheries of the plate boundary.

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.

Fault growth in the upper crust is mainly achieved by the accumulation of slip during earthquakes. Large faults with cumulative displacements of kilometres experience hundreds of large magnitude earthquakes but the precise manner in which maximum earthquake size evolves over millions of years is uncertain. To bridge the gap between faulting on earthquake (e.g. 1 Ma) timescales we examine the Cape Egmont Fault in offshore New Zealand, using good quality seismic-reflection data tied to wells and seabed bathymetry. Displacements on nine horizons, including the seabed, three horizons of 14–225 ka in age and five horizons of 5.3–1.6 Ma in age, were mapped along the ca. 70 km length of the fault. These horizons record maximum displacements ranging from 6 to 2344 m and suggest that this active fault commenced its latest phase of movement about 3.7 Ma ago. Displacement profiles for all horizons and inter-horizon increments are of similar geometry, indicating an approximately constant fault length and fixed maximum displacement position during growth. Fault length was established rapidly and inherited from an underlying Cretaceous structure with fault dimensions in the overlying sequence mainly achieved by up-dip propagation. As the magnitude of earthquakes is proportional to their rupture length, the maximum size of earthquakes on the fault remained constant for at least the last 3.2 Ma, with the distribution of slip along the fault during these events approximately comparable. This contrasts with the maximum displacement rates which varied by an order of magnitude during the last 3.7 Ma (0.18–2.8 mm/yr). Decreases in displacement rates were accompanied by proportional increases in the average earthquake recurrence intervals (ca. 1.3–18 ka), and reflect regional changes in the rates of extension.

A series of large hydrothermal eruptions occurred across the Waiotapu geothermal field at about the same (prehistoric) time as the ~AD1315 “Kaharoa” rhyolite magmatic eruptions from Tarawera volcano vents, 10–20 km distant. Triggering of the Waiotapu hydrothermal eruptions was previously attributed to displacement of the adjacent Ngapouri Fault. The Kaharoa rhyolite eruptions are now recognised as primed and triggered by multiple basalt intrusions beneath the Tarawera volcano. A ~1000 t/day pulse of CO2 gas is recorded by alteration mineralogy and fluid inclusions in drill core samples from Waiotapu geothermal wells. This CO2 pulse is most readily sourced from basalt intruded at depth, and although not precisely dated, it appears to be associated with the Waiotapu hydrothermal eruptions. We infer that the hydrothermal eruptions at Waiotapu were primed by intrusion of the same arrested basalt dike system that drove the rhyolite eruptions at Tarawera. This dike system was likely similar at depth to the dike that generated basalt eruptions from a 17 km-long fissure that formed across the Tarawera region in AD1886. Fault ruptures that occurred in the Waiotapu area in association with both the AD1886 and ~AD1315 eruptions are considered to be a result, rather than a cause, of the dike intrusion processes.

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...

Sediment cores collected in a coastal lagoon a few kilometres east of Wairoa, northern Hawke's Bay, New Zealand, were examined using sedimentological, geochemical, palynological and micropaleontological analyses. A distinct short-lived catastrophic saltwater inundation (CSI) about 6300 years BP and possibly other minor marine incursions are preserved in the coastal estuarine to lagoonal freshwater sedimentary sequences, which have been deposited in the last 6500 years. The CSI is characterised by a gravel unit that thins landward and decreases in particle size to sand, within a sequence consisting mainly of brackish estuarine muds. Diatom assemblages indicate a marked change from the shallow brackish estuarine muds to marine gravels and sands to brackish estuarine muds. The marine influence in the gravel and sand is also shown by the presence of marine dinoflagellates and a peak in Na/Rb. Sedimentological, chemical and paleontological (in particular diatoms) evidence indicates it is a CSI. We conclude that this was a tsunami and propose the most likely propagating mechanisms. Marine influence decreases upcore and totally freshwater conditions are evident in the upper section of the cores. The geochemistry of the sediments mainly reflects the change in stratigraphy, with distinct signatures for tephra (Na, Fe, Cr), organic-rich and peat units (As, Br) and the coarse gravel-sand CSI unit (Na/Rb, Cr, Fe), but it is also indicative of changes in depositional environment. The change in chemistry (Na/Rb) in the CSI event is indicative of a saltwater influence, whereas a marked change in S content suggests a sudden change from brackish to freshwater conditions shortly after 4800 years BP. Another peak in S and Br content about 3200 years BP may indicate another temporary change to brackish conditions.

[EN] The El Salvador Fault Zone, firstly identified after the 13th February 2001 Mw 6.6 El Salvador earthquake, is a 150 km long, 20 km wide right-lateral strike-slip fault system. Ruptures along the ESFZ are thought to be responsible for most of the historical destructive earthquakes along the El Salvador Volcanic Arc, as well as for most of the current seismicity of the area. In this work, we focus on the geological setting of the fault zone by describing its geomorphology and structure, using field-based observations, digital terrain modelling, and aerial photograph interpretation with the aim at contributing to the understanding of the ESFZ slip behaviour. In particular, we address the ESFZ structure, kinematics and evolution with time. The ESFZ is a complex set of traces divided in major rupture segments characterized by different geometry, kinematics and geomorphic expressions. Natural fault exposures and paleoseismic trenches excavated along the fault show that the strike-slip deformation is distributed in several planes. Both geometry and kinematics of the fault zone are consistent with a transtensional strain regime. The estimated geological slip rate for the main fault segments by paleoseismic trenches and displaced geomorphic features implies a deficit in velocity of the fault compared to the available GPS velocities data. The high vertical scarps of some fault segments would require Quaternary slip rates not coherent neither with measured GPS velocities nor with slip rates obtained from paleoseismic analysis. This mismatch suggests a pre-existing graben structure that would be inherited from the previous regional roll back related extensional stage. We consider that the ESFZ is using this relict structure to grow up along it. As a result, we propose a model for ESFZ development consistent with all these observations., [ES] La Zona de Falla de El Salvador (ZFES) es un sistema de falla de desgarre dextral de 150 km de longitud y 20 de anchura, que fue identificada por primera vez después del terremoto de Mw 6.6 de El Salvador de febrero de 2001. La mayoría de la sismicidad y de los terremotos históricos destructivos producidos en el arco volcánico salvadoreño han sido producidos por la ruptura de la ZFES. Este trabajo se centra en el marco geológico de la zona de falla describiendo su geomorfología y su estructura a través de observaciones de campo, del estudio de los modelos digitales del terreno y de la interpretación de las fotografías aéreas, con el objetivo de avanzar en el conocimiento del comportamiento de la ZFES. En concreto trataremos del estudio de la estructura, la cinemática y la evolución de la ZFES. La ZFES es un complejo sistema de fallas divididas en varios segmentos que se diferencian en la geometría, la cinemática y la expresión geomorfológica. En los afloramientos de la falla, así como en las trincheras paleosismicas excavadas se ha observado que la deformación de desgarre está distribuida en varios planos y tanto la geometría como la cinemática de la zona de falla indican que la ZFES está bajo un régimen de deformación transtensional. La tasa de deformación estimada para los principales segmentos a través del estudio paleosísmico y del análisis de indicadores geomorfológicos desplazados nos muestra un déficit de velocidad para la falla si lo comparamos con los datos obtenidos por GPS. Estos datos tampoco ayudan a explicar la existencia de grandes escarpes verticales que se observan en algunos segmentos de la falla, y que requerirían tasas de deformación muy elevadas. Esta discrepancia sugiere la existencia de una estructura de graben preexistente que puedo ser producida por el “roll-back” de la placa y que creó una fase extensional en el arco volcánico. En este trabajo consideramos que la ZFES está actualmente desarrollándose sobre la estructura extensional relicta y como resultado proponemos un modelo estructural consistente con estas observaciones.

An extensive terrace (Waipaoa-1) that can be traced for about 29 km in the Waipaoa valley, eastern North Island, New Zealand, is underlain by at least 10 m of coarse, aggradational, river gravels. Terrace cover beds contain tephras erupted from central North Island volcanoes and these provide minimum ages for the underlying gravels. Tephra or tephric layers occurring in the lower cover beds were investigated at five sites using a combination of stratigraphy, mineralogy, and the major element composition of glass shards together with discriminant function analysis (DFA). The basal tephra is identified as the ca. 14,700 14C years old (ca. 17,700 cal. years B.P.) Rerewhakaaitu Tephra, erupted from Okataina Volcanic Centre. Using the stratigraphic relationship of Rerewhakaaitu Tephra, the end of aggradation is dated at ca. 15,000 14C years (ca. 18,000 cal. years). Correlation with aggradational terraces elsewhere in North Island and northern South Island indicates that aggradation ended at the same time over a wide area and confirms a climatic origin for the terraces. Subsequent downcutting was apparently rapid because Rerewhakaaitu Tephra also occurs at the base of cover beds on a ca. 15 m lower terrace. The downcutting represents a major change in river dynamics and is most likely the response to climatic change and the resultant upper catchment landscape stability.

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...

Descriptive accounts and analysis of local seismograms establish that the epicentre of the 1934 March 5 Ms7.6 earthquake, known as the Pahiatua earthquake, was nearer to Pongaroa than to Pahiatua. Conspicuous and severe damage (MM8) in the business centre of Pahiatua in the northern Wairarapa led early seismologists to name the earthquake after the town, but it has now been found that the highest intensities (MM9) occurred about 40 km to the east and southeast of Pahiatua, between Pongaroa and Bideford. Uncertainties in the location of the epicentre that have existed for sixty years are now resolved with the epicentre determined in this study lying midway between those calculated in the 1930's by Hayes and Bullen. Damage and intensity summaries and a new isoseismal map, derived from extensive newspaper reports and from 1934 Dominion Observatory "felt reports", replace previous descriptions and isoseismal maps. A stable solution for the epicentre of the mainshock has been obtained by analysing phase arrivals read from surviving seismograms of the rather small and poorly equipped 1934 New Zealand network of twelve stations (two privately owned). The addition of some teleseismic P arrivals to this solution shifts the location of the epicentre by less than 10 km. It lies within, and to the northern end of, the MM9 isoseismal zone. Using local instrumental data larger aftershocks and other moderate magnitude earthquakes that occurred within 10 days and 50 km of the mainshock have also been located. Approximate locations of other associated moderate magnitude earthquakes until October 1934 have been identified by their maximum intensity and S-P intervals read from the Wellington Wood-Anderson seismograph records. The distribution of S-P intervals of aftershocks (magnitudes M > 3.5) within 24 hours of the mainshock is used to delineate the probable mainshock rupture zone. Neither contemporary sources nor recent inquiries directed to old residents yield historical evidence of a surface fault rupture. Nevertheless, the strike-slip mechanism at 20 km depth determined by preliminary teleseismic body wave modelling of Doser and Webb suggests that rupture could have extended to the surface. Recent investigation of two of the freshest-looking, active faults that lie within the MM9 isoseismal by Schermer and others indicates that one of them could have ruptured in the 1934 Pahiatua earthquake.

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...