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The Hikurangi subduction margin, New Zealand, has not produced large subduction earthquakes within the short written historic period (~180 years) and the potential of the plate interface to host large (M > 7) to great (M > 8) earthquakes and tsunamis is poorly constrained. The geological record of past subduction earthquakes offers a method for assessing the location, frequency and approximate magnitude of subduction earthquakes to underpin seismic and tsunami hazard assessments. We review evidence of Holocene coseismic coastal deformation and tsunamis at 22 locations along the margin. A consistent approach to radiocarbon age modelling is used and earthquake and tsunami evidence is ranked using a systematic assessment of the quality of age control and the certainty that the event in question is an earthquake. To identify possible subduction earthquakes, we use temporal correlation of earthquakes, combined with the type of earthquake evidence, likely primary fault source and the earthquake certainty ranking. We identify 10 past possible subduction earthquakes over the past 7000 years along the Hikurangi margin. The last subduction earthquake occurred at 520–470 years BP in the southern Hikurangi margin and the strongest evidence for a full margin rupture is at 870–815 years BP. There are no apparent persistent rupture patches, suggesting segmentation of the margin is not strong. In the southern margin, the type of geological deformation preserved generally matches that expected due to rupture of the interseismically locked portion of the subduction interface but the southern termination of past subduction ruptures remains unresolved. The pattern of geological deformation on the central margin suggests that the region of the interface that currently hosts slow slip events also undergoes rupture in large earthquakes, demonstrating different modes of slip behaviour occur on the central Hikurangi margin. Evidence for subduction earthquakes on the northern margin has not been identified because deformation signals from upper plate faults dominate the geological record. Large uncertainties remain in regard to evidence of past subduction earthquakes on the Hikurangi margin, with the greatest challenges presented by temporal correlation of earthquake evidence when working within the uncertainties of radiocarbon ages, and the presence of upper plate faults capable of producing deformation and tsunamis similar to that expected for subduction earthquakes. However, areas of priority research such as improving the paleotsunami record and integration of submarine turbidite records should produce significant advances in the future.

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...

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...

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 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.

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...

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

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 ...

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

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...

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...

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...

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.

The Canterbury Earthquake Sequence of 2010–2011 caused regional tectonic subsidence and uplift. The observed slip distributions and fault locations were used to develop models of the 3-D tectonic deformation throughout the region, for each earthquake. The earthquake sequence also triggered widespread liquefaction causing subsidence and localized lateral spreading. These were both mapped by land damage assessment teams for the Earthquake Commission. Land was categorized on the basis of observed land and foundation damage to differentiate the amounts of geotechnical investigation and foundation design effort required to address the potential for liquefaction. Aerial LiDAR (light detection and ranging) surveys were used to quantify the surface deformations and, by subtracting the estimated vertical tectonic movements, the subsidence attributable to liquefaction, which correlated well with areas observed to be affected by liquefaction. Horizontal ground surface movements were also estimated using sub-pixel correlation of pairs LiDAR data sets. Horizontal movements within the soil layers were estimated by subtracting the tectonic movements, which correlated well with lateral spreading observations.

[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.

We present the main results of a probabilistic seismic hazard assessment of the Canterbury region recently completed for Environment Canterbury (formerly Canterbury Regional Council). We use the distribution of active faults and the historical record of earthquakes to estimate the levels of earthquake shaking (peak ground acceleration and response spectral accelerations) that can be expected across the Canterbury region with return periods of 150, 475 and 1000 years. The strongest shaking (e.g. 475 year peak ground accelerations of 0.7g or more) can be expected in the west and north to northwest of the Canterbury region, where the greatest concentrations of known active faults and historical seismicity are located. Site-specific analyses of eight towns and cities selected by Environment Canterbury show that Arthur's Pass and Kaikoura are located within these zones of high hazard. In contrast, the centres studied in the Canterbury Plains (Rangiora, Kaiapoi, Christchurch, Ashburton, Temuka and Timaru) are generally located away from the zones of highest hazard. The study represents the first application of recently-developed methods in probabilistic seismic hazard at a regional scale in New Zealand.

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...

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

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.

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.

The destruction of the Fukushima Daiichi Nuclear Power Plant (NPP) following the March 2011 Tohoku earthquake and tsunami brought into sharp focus the susceptibility of NPPs to natural hazards. This is not a new issue—seismic hazard has affected the development of plants in the United States, and volcanic hazard was among the reasons for not commissioning the Bataan NPP in the Philippines [Connor et al., 2009].

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....

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.

Fault behaviour appears to be different in different tectonic provinces of New Zealand. Uplifted Holocene marine terraces along the east coast of the North Island suggest time-predictable behaviour on reverse faults of the Hikurangi subduction margin. Major dextral faults of the strike-slip fault province in central New Zealand appear to show characteristic slip behaviour. Short normal faults in the Central Volcanic Region show highly variable increments of displacement. Finally, reverse faults of the Central Otago and Northwest Nelson region may have intermittently characteristic patterns of activity. Each of these behaviour patterns has been observed elsewhere, although, where there are good data to constrain the actual dates of palaeoearthquakes, a uniform slip or coupled model best explains most situations. Temporal and spatial clustering of fault rupture and major earthquakes are increasingly being recognized. It is crucial to obtain better dates and to determine the extent of individual rupture segments in order to better characterize fault behaviour. Non-characteristic fault behaviour has serious implications for current methods of seismic hazard evaluation. Seismic hazard studies should utilize specific fault data in preference to assuming a particular fault behaviour model.

Geological observations require that episodic slip on the Alpine fault averages to a long-term displacement rate of 2-3 cm/yr. Patterns of seismicity and geodetic strain suggest the fault is locked above a depth of 6-12 km and will probably fail during an earthquake. High pore-fluid pressures in the deeper fault zone are inferred from low seismic P-wave velocity and high electrical conductivity in central South Island, and may limit the seismogenic zone east of the Alpine fault to depths as shallow as 6 km. A simplified dynamic rupture model suggests an episode of aseismic slip at depth may not inhibit later propagation of a fully developed earthquake rupture. Although it is difficult to resolve surface displacement during an ancient earthquake from displacements that occurred in the months and years that immediately surround the event, sufficient data exist to evaluate the extent of the last three Alpine fault ruptures: the 1717 AD event is inferred to have ruptured a 300-500 km length of fault; the 1620 AD event ruptured 200-300 km; and the 1430 AD event ruptured 350-600 km. The geologically estimated moment magnitudes are 7.9 ± 0.3, 7.6 ± 0.3, and 7.9 ± 0.4, respectively. We conclude that large earthquakes (Mw >7) on the Alpine fault will almost certainly occur in future, and it is realistic to expect some great earthquakes (Mw ≥8).

The Conway Segment of the dextral-slip Hope Fault is one of the fastest slipping fault segments along New Zealand s plate boundary, but has not ruptured co-seismically in the historic period and little paleoseismic data exist to constrain its large earthquake record. Two paleoseismic trenches were opened adjacent to Greenburn Stream near Kaikoura for the 2001 ILP Paleoseismology Conference. Both trenches were excavated into deposits ponded against an uphill-facing shutter scarp. Trench 1, dug through a cobbly soil and surface deposit was dominated by a thick fan/fluvial sequence that was radiocarbon dated at 4409 ± 60 C14 years BP (4844-5288 cal years BP) at the base of the trench. This trench exhibited evidence of complex deformation from many paleoseismic events. The most recent earthquakes are difficult to constrain due to a lack of cover stratigraphy on the fan deposits. However, the modern soil appears to be faulted and is covered by cobbles with a weathering rind-derived age of 220 ± 60 years. Trench 2, dug ?? 50 m to the west has an expanded sequence of the younger cover deposits. Paleoseismic event horizons have been recognised from the combined evidence of upwardterminating faults, offset and mismatched units, a sandblow deposit, and abrupt landscape change shown by the burial of paleosol surfaces that form the event horizons. Two paleosols underlying the modern soil are clearly faulted by two separate rupture events. A dome of sand interpreted as a liquefaction sandblow deposit overlies the lower paleosol (event horizon). Both paleosols are overlain by metre-thick debris deposits, interpreted as earthquake-induced rock avalanches that cascaded off the hillslope following Mw 7 + events. Four radiocarbon dates place some constraints on the timing of the three recent surface-rupturing events. The youngest and lowest date is 548 ± 60 C14 years BP (504-656 cal years BP) and occurs below the lower paleosol. It constrains the maximum duration of time in which the last 2 earthquake events occurred to be 545 years (1295-1840 A.D.). This is consistent with the average Recurrence Interval (RI) of 180-310 years that we determine using two independent paths. The soil record indicates that each event is separated by a significant period of time, comparable to the calculated RI. The most recent event is constrained between ca. 1780 A.D. ± 60 years, taking into account the dates from these trenches, a weathering rind age, and from stratigraphic correlation at the site. Event III probably occurred before 1220 A.D. A maximum dextral slip rate of 23 ± 4 mm/yr is calculated from the minimum fan age and the offset/deflection of a stream channel along the shutter ridge. In concert with the estimate of single event displacement (5-6 m), these results show that the Conway Segment of the Hope Fault is fast-slipping and has ruptured regularly as a result of large earthquakes prior to the European colonisation of New Zealand.

De Pascale et al. (2014) present a new “bimodal” fault rupture behavior model for the dextral-reverse Alpine fault using evidence from several new, small (

International audience; This paper presents preliminary results for three GPR profiles acquired across the Wellington active strike-slip fault within the Wellington urban area. In this sector, it is suggested that the subsurface geometry (8-10 m) of the fault comprises twomain deforming strands that bound narrow transpressive and transtensive sections. The location of fault planes interpreted from radargrams closely corresponds with the inferred location of the main fault at the ground surface. Despite noise due to the urban settings, GPR proved to be a technique capable of locating fault strands, thus potentially providing useful data in targeting areas for palaeoseismic studies, such as trenching.

[1] The 1957 Gobi Altay M8.3 earthquake in southern Mongolia was associated with the simultaneous rupture of several faults, including the Gurvan Bulag reverse fault, which is located about 25 km south of the main strike-slip Bogd fault. Our study of paleoseismic excavations across the Gurvan Bulag fault suggests that the penultimate surface rupture occurred after 6.0 ka, most likely between 2.6 and 4.4 ka, and a possible earlier rupture occurred after 7.3 ka. Our interpretation of the stratigraphic relations in one of the exposures suggests that at least five earthquakes have generated surface rupture of the Gurvan Bulag fault since the abandonment of an ancient alluvial fan surface. Luminescence dating of sediment associated with this surface indicates that it formed either 26.6 ± 2.1 ka or 16.1 ± 2.0 ka. These data imply that the recurrence intervals for surface faulting on the Gurvan Bulag and Bogd faults are similar, on the order of several thousands of years, but that the penultimate surface ruptures of the two faults did not occur during the same earthquake.

Histories of movement on several active faults have been determined and used to evaluate possible future seismic hazard in the Rangitaiki Plains. The eruption of Kaharoa Ash c. 800 years B. P. provides a datum to establish the history of faulting. The Matata, Edgecumbe, Onepu, and Rotoitipakau Faults, all located in the southern and western Rangitaiki Plains, have moved at least once during the last 800 years. In contrast, faults in the eastern part of the Rangitaiki Plains do not show evidence of post-Kaharoa movement. The past level of seismic hazard has, therefore, been lower in the eastern part of the plains compared with southern and western areas. We assume that rupture of the northeast-trending normal faults in the Rangitaiki Plains will produce isoseismal patterns similar to that observed during the 1987 March 2 Edgecumbe earthquake. By overlaying the MM IX isoseismal of the Edgecumbe earthquake over each fault in the Rangitaiki Plains, and taking into account geological data on the recur...

The Edgecumbe earthquake, 1987 March 2 (M L 6. 3), was associated with renewed tectonic rupture on the Edgecumbe Fault, renewed movement on the Onepu and Rotoitipakau Faults, and several new surface breaks—the Awaiti, Otakiri, Te Teko, and Omeheu Faults. These northeast trending tectonic ruptures are widely distributed across the Rangitaiki Plains, range in length from 0. 5 to 7 km, and are mostly downthrown to the northwest. They are associated with warping and prominent fissuring. Maximum displacement, 2. 5 m vertical and 1. 8 m extensional, occurred near the middle of the Edgecumbe Fault trace. Trenching investigations revealed that perhaps two faulting events have occurred in the past 1850 years in addition to the 1987 event; the earlier one is unsubstantiated, but may have occurred at about 1850 years B. P., and another occurred at about 800 years B. P. (the time of deposition of the Kaharoa Ash). The 800 year B. P. event was associated with warping, but little fissuring. An average slip vec...

Both the South Island of New Zealand and the Transverse Ranges of California have (1) a major right-slip fault marking the plate boundary, (2) a left-stepping bend in the fault resulting in ranges and basins bounded by active reverse faults that strike 45° counterclockwise to the regional strike of the main fault, (3) a set of right-slip faults on one side of the constraining bend, with most of the total displacement concentrated On the fault stepped farthest left from the continuation of the fault on the other side of the bend, and (4) intersections between the set of faults and the main fault within the bend not present or poorly defined. The faults with most of the displacement (Alpine-Wairau, San Andreas) may pre-date the constraining bend, The reverse fault province southeast of the Alpine fault is separated from that fault by the Southern Alps, which may be underlain by crust that is too hot and too weak to sustain major reverse faults. Average reverse fault recurrence intervals in New Zealand and California are 10³ to 2 × 104 years as compared to less than 10³ years for the right-slip master fault, Seismicity is high but patchy in the Nelson-Buller region of the northern South Island, low but patchy in the Transverse Ranges, and very low in Central Otago in the southern South Island, all reverse fault provinces. Seismicity patterns in both regions, poorly related to overall late Quaternary fault distribution, correspond largely to individual rupture events on portions of Quaternary faults, and the seismic inactivity of many of these faults may simply represent quiescence between seismic faulting with long recurrence intervals. The geology and Seismicity of the three reverse-fault provinces support the suggestion of C. R. Allen [1975] that late Quaternary fault history is a better long-term guide for assessment of large-magnitude earthquake hazard than instrumental and historical Seismicity for faults with long recurrence intervals.

Tectonic processes have both very pronounced and very subtle effects on the earth’s crust, which may be measured by the deformation of datum planes at the earth’s surface. The position of sea level with respect to adjacent landmasses may be regarded as a datum plane that records the interplay between climatic, geodynamic and tectonic processes through time.

Trenching of two fault strands that form part of the 21 km long, and up to 2 km wide Whirinaki Fault, Taupo Rift, New Zealand, shows that surface fault rupture has occurred at least eight times during the past 26.5 kyr. Single‐event displacements on each strand vary from a few decimetres to perhaps >2.5 m. Fault trace mapping, geomorphic analysis, and paleoseismic studies indicate a maximum magnitude for the Whirinaki Fault of c. Mw 6.6, with a recurrence interval of between 1000 and 4000 yr. The variability of single‐event displacement and timing of rupture on the two strands is attributed to various unsegmented and segmented rupture modes. Airfall tephra revealed in the trenches span the past 26.5 kyr, and provide time horizons to enable interpretation of how slip has accumulated on each of the strands of the fault. Temporal variation in slip rate ranges from 0.3 to 1.5 mm/yr and is indicative of spatial and temporal changes in the locus of strain in the Taupo Rift and the interdependence of th...