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We summarise the geological setting of complex surface rupture of the 2016 Mw 7.8 Kaikōura earthquake in the Marlborough Tectonic Domain of New Zealand. The event was complex both seismologically and geologically but not totally dissimilar to other large historical events globally. The earthquake occurred in the comprehensively imbricated, steeply-dipping Pahau Terrane crust that exhibits numerous tectonic overprints with diverse faulting styles. The current strike slip faults of the Marlborough Fault System are immature in their structural development and occupy, at least in part, inherited faults of earlier deformation phases. Several of the faults that ruptured in 2016 may connect at seismogenic depths. A listric fault geometry is likely for many of the faults that ruptured in 2016. This interpretation is supported by crustal seismic mapping identifying listric geometries for other large faults within the region. Examination of other historic surface rupturing earthquakes in the Marlborough Tectonic Domain and globally show some complexity but not to the same level of multifault rupture as in 2016. We conclude that multifault ruptures may be enhanced in the Kaikōura region where the Australian plate crust is thinner than farther west and the plate boundary deformation, at rates of >20 mm year-1, transfers between closely-spaced faults with acute changes in surface geometry and with diverse rupture characteristics. The trend in seismic hazard assessment since 2016 is to include multifault ruptures universally, but this would be inconsistent with historic events in the Marlborough Tectonic Domain. Consideration of geological structure and history may usefully be incorporated into seismic hazard methodology to evaluate when and where multifault source models are indeed appropriate. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

The c. 15 km-long Ngapouri-Rotomahana Fault (NRF) is a major splay of the Paeroa Fault at the eastern margin of the modern Taupō Rift, the active tectonic structure embedded within the Taupō Volcanic Zone of North Island, New Zealand. The NRF and Paeroa Fault extend to the southern margin of the Okataina Volcanic Centre (OVC) and lie southwest of the Tarawera vent lineation, which is the source of approximately half of the eruptions of the OVC in the past 25 cal. ka BP. Here, we explore volcano-tectonic relationships between the OVC and the NRF and Paeroa Fault. Collective evidence used in our analysis includes: volcanic processes interpreted as occurring during the historic 1886 Tarawera (basalt) and the prehistoric 1314 ± 12 CE Kaharoa (basalt triggered rhyolite) eruptions, both on the Tarawera vent lineation; exposures in five trenches excavated across the NRF and seven trenches across the Paeroa Fault; data on a series of explosion craters formed to the southwest of the volcano associated with the ~1314 CE Kaharoa eruption and the Rotoma rhyolite (~9.4 cal. ka BP) eruption from the OVC; and mafic dykes that primed several of the OVC eruptions. Data from the twelve trenches on the two faults reveal eight surface fault ruptures since 15.6 cal. ka BP, with most closely coinciding with volcanic eruptions, providing a first-order indication of probable causality. Three principal modes of interaction are identified. Firstly, large displacement events on the Paeroa fault, arguably immediately prior to the Mamaku and Rotoma rhyolite eruptions (~7.9 and ~9.4. cal. ka BP, respectively) and on the NRF immediately prior to the ~1314 CE Kaharoa eruption are candidates for earthquake static or dynamic stress triggers for those explosive eruptive events. Secondly, basalt dyke intrusion was also involved in the initiation of the Kaharoa eruption, so the spatial and temporal relationships between dyke intrusion, smaller displacement fault ruptures and initiation of the Kaharoa eruption appear closely connected. Thirdly, faulting events that are interpreted as co- or post-eruption may be the result of stress triggers associated with magma chamber deflation. • Spatial and temporal associations between fault ruptures and eruptions indicate linked processes. • Fault ruptures occur immediately before, during and shortly after volcanic eruptions. • Static stress transfer is a likely trigger between fault rupture and volcanic eruption or caldera deflation. • Basalt dykes interact with active faults at caldera margins as well as rhyolite magma chambers. [ABSTRACT FROM AUTHOR]

The scarcity of long geological records of major earthquakes, on different types of faults, makes testing hypotheses of regular versus random or clustered earthquake recurrence behavior difficult. We provide a fault-proximal major earthquake record spanning 8000 years on the strike-slip Alpine Fault in New Zealand. Cyclic stratigraphy at Hokuri Creek suggests that the fault ruptured to the surface 24 times, and event ages yield a 0.33 coefficient of variation in recurrence interval. We associate this near-regular earthquake recurrence with a geometrically simple strike-slip fault, with high slip rate, accommodating a high proportion of plate boundary motion that works in isolation from other faults. We propose that it is valid to apply time-dependent earthquake recurrence models for seismic hazard estimation to similar faults worldwide. [ABSTRACT FROM AUTHOR]

Abstract: 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 2.2km long section of the Waihuka tributary (217km2) of the Waipaoa River (2150km2) in eastern North Island, New Zealand, a sequence of at least ten fluvial terraces and abandoned meanders up to 45m 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 10–8ka 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 2km/kyr. In the period before and after rapid downcutting in the Waihuka tributary, modest incision rates, averaging 1–2mm/yr, probably represent the regional tectonic uplift rate. [Copyright &y& Elsevier]

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 m. From these data a mean dip-slip rate of c. 0.1 mm/yr and a maximum recurrence interval of 4490-6900 yr, can be calculated. if the Repongaere Fault is representative of other Raukumara Peninsula normal faults, then this relatively low rate of activity supports the interpretation that these faults are not contributing significantly to the deformation of the Raukumara Peninsula. The low rate of activity is also consistent with the very localised evidence for landscape impacts, a calculated moderate Mw of 6.3-6.7, and the fault's location within the lower part of the Waipaoa River catchment. Together, these observations suggest that Repongaere Fault earthquakes have minimal, localised impact on the Waipaoa Sedimentary System. [ABSTRACT FROM AUTHOR]

The 30 km long Paeroa Fault is one of the largest and fastest slipping (c. 1.5 mm/yr vertical displacement rate) normal faults of the currently active Taupo Rift of North island, New Zealand. Along its northern section, seven trenches excavated across 5 of 11 subparallel fault strands show that successive ruptures of individual strands probably occurred at the same time, but were individually and collectively highly variable in size and recurrence, and most fault strands have ruptured three or four times in the past 16 kyr. in the c. 16 kyr timeframe, four surface-rupturing earthquakes took place when Okataina volcano was erupting, and six occurred between eruptions. Large earthquakes on the Paeroa Fault comprise a significant component of the seismic hazard in the region between the Okataina and Taupo Volcanic Centres, and there are partial associations between these large earthquakes and volcanism. [ABSTRACT FROM AUTHOR]

Abstract: A sequence of fluvio-estuarine sediments exposed beneath the highest Holocene marine terrace at Pakarae, North Island, New Zealand, records the early-mid Holocene infilling of the Pakarae valley. This sequence was developed on an active, coseismically uplifting coastline and provides a valuable comparison to widely used facies models for estuaries, which were developed exclusively from stable coastal settings. We describe eight sedimentary sections, distributed along a 220 m stretch of riverbank and present twelve new radiocarbon ages. Sedimentology and benthic foraminifera are used to divide the sequence into eight bio-lithofacies. These units are grouped into four paleoenvironmental facies associations: barrier, estuarine, estuary-head delta and floodplain. We compare the distribution of the Pakarae paleoenvironmental facies associations to those in models of incised valley infill sequence models and case studies of infilled valleys. These data allow us to present new contributions to the development of a facies model for the sedimentary infilling of an incised valley system that was experiencing coseismic uplift synchronous with deposition. We suggest the distinctive characteristics of such a model would include (1) part, or all, of the transgressive and lowstand sequences may now lie above modern sea level, (2) the transgressive sedimentary sequence is typically condensed relative to the coeval amount of eustatic sea level (SL) rise that occurred during that period, and (3) evidence of relative SL falls, such as transitions from estuarine to fluvial environments, despite conditions of rapid and continuous eustatic SL rise. [Copyright &y& Elsevier]

Abstract: 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 >1mmyr−1 adjacent to a subduction zone and it provides a valuable comparison to subduction zones dominated by great earthquakes. [Copyright &y& Elsevier]

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 <0.91 ka (T7). The average Holocene tectonic uplift rate at Pakarae is 3.2 ± 0.8 mm/yr. The abandonment of each terrace, from T2 to T7, probably took place after a discrete uplift event. The average time interval between these events is 850 ± 450 yr and the average uplift magnitude is 2.7 ± 1.1 m per event. We infer that uplift has been accommodated by slip on an offshore reverse fault. Normal slip on the Pakarae Fault, at right angles to the margin, occurs at a comparatively slower rate and has probably made little contribution to coastal uplift. [ABSTRACT FROM AUTHOR]

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 least 1811 yr since the last surface rupture, and an average slip rate estimate for the Wairau Fault of 3-5 mm/yr, suggests that at least 5.4 m and up to 11.5 m of elastic shear strain has accumulated since the last rupture. This is near to or greater than the single-event displacement estimates of 5-7 m. The average recurrence interval for surface rupture of the fault determined from the trench data is 1150-1400 yr. Although the uncertainties in the timing of faulting events and variability in inter-event times remain high, the time elapsed since the last event is in the order of 1-2 times the average recurrence interval, implying that the Wairau Fault is near the end of its interseismic period. [ABSTRACT FROM AUTHOR]

Abstract: A correlation of fluvial terraces is presented for eight non-glacial catchments of the eastern North Island, New Zealand, within the actively uplifting Hikurangi Margin. Using a combination of loess and tephra coverbed stratigraphy, and radiocarbon and OSL dating of fluvial deposits and loess coverbeds, we demonstrate correlation of four fill terraces, T1–T4. The available age constraints suggest T1=15–30 ka, T2=31–50 ka, T3=50–70 ka, and T4=∼115 ka, but the association and temporal link with loess deposits suggest correlation with cold periods, and thus the refinement of T2=late MIS 3 (31–40 ka), T3=MIS 4 (55–70 ka), T4=MI Substage 5b (∼90 ka), 5d (∼110 ka), or MIS 6 (∼140–160 ka). The ability to correlate terraces between catchments, plus the lack of independent evidence for tectonic triggering events, indicates terraces have probably formed in response to either climate (terrestrial) or baselevel (sea level) control. Climate control is indicated by the temporal link of post-glacial incision with re-establishment of forest cover, and of LGM aggradation with limited grass and shrub cover and periglacial processes. Aggradation due to increased sediment supply under reduced vegetation is dramatically demonstrated by formation of the Taupo Pumice Alluvium terrace in response to inundation by volcanic deposits (unwelded ignimbrite) following the 1.8 ka Taupo eruption, and the response to post-settlement (&#60;500 yr BP) deforestation. The upstream limit of post-glacial baselevel control is recorded by a post-glacial sediment wedge burying older terraces in six catchments. In one catchment, the inner (landward) edge of the wedge is a mid-Holocene fill terrace, interpreted to have formed in response to the post-glacial sea level highstand, and thus is a baselevel-controlled terrace. Evidence defining the downstream extent of climate control during the LGM (and thus the upstream limit of baselevel-controlled lowstand incision) is now buried beneath the continental shelf, but limited fluvial features on the inner shelf (&#60;20 km offshore), and LGM aggradation despite a range of shelf gradients indicate climate-induced aggradation probably extended at least to the present day inner shelf. [Copyright &y& Elsevier]

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 Mw 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 Mw 8.1 earthquake, or consecutively, could explain larger amounts (>1.5 m) of coastal subsidence. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

Abstract: 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 (~10000–7000cal. yr BP), (ii) a sequence of post-7000cal. 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 10–24km 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. [Copyright &y& Elsevier]

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 the displacement rates and paleoearthquakes in the area. [ABSTRACT FROM AUTHOR]

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 the Porewan loess of OIS 4, indicating the Te Papa Terrace formed during OIS 5a or earlier. Regardless of terrace age, the morphology of the terraces shows the coastal uplift mechanism is not related to upper plate faults, but is probably driven by deep-seated subduction zone processes. [ABSTRACT FROM AUTHOR]

Paleoearthquakes at Earth's surface often generate faults with variable displacement rates over short time intervals (e.g., <18 k.y.). The nature and origin of these variations and the extent to which they result from systematic, and therefore predictable, earthquake processes is unresolved. We examine the processes underlying fluctuations in displacement rates by charting the accumulation of displacement over the last 60 k.y. on 25 normal fault traces distributed across the Taupo Rift, New Zealand. Displacement rates become more stable with increasing fault size and are uniform when aggregated across the entire rift. The increased stability of fault displacement rates at greater spatial scales suggests that each fault is a component of a kinematically coherent system in which all faults interact and their earthquake histories are interdependent. Fault interdependencies generate short-term complex (<18 k.y.) fluctuations in the timing and magnitude of earthquakes, but also ultimately result in the stability of displacement rates on million-year time scales. [ABSTRACT FROM AUTHOR]

Abstract: 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. <100ka) and geological (e.g. >1Ma) 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 14–225ka in age and five horizons of 5.3–1.6Ma in age, were mapped along the ca. 70km length of the fault. These horizons record maximum displacements ranging from 6 to 2344m and suggest that this active fault commenced its latest phase of movement about 3.7Ma 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 3.2Ma, 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 3.7Ma (0.18–2.8mm/yr). Decreases in displacement rates were accompanied by proportional increases in the average earthquake recurrence intervals (ca. 1.3–18ka), and reflect regional changes in the rates of extension. [Copyright &y& Elsevier]

Infrastructure networks (e.g. transport, water, energy, telecommunications) support life and the economy of communities of all sizes. New Zealand has witnessed several damaging earthquakes in the last decade that provide a compelling case to accelerate building resilient infrastructures in the country, so we can minimize any adverse impacts from future earthquakes. One of the regions that is highly vulnerable to earthquakes is Wellington. With the region's population continually expanding and placing increasing demand on its ageing infrastructures, with limited redundancy in the networks, and with many of its assets close to and / or intersecting fault lines, a large earthquake in the region could be highly disruptive, potentially resulting in serious social and economic consequences. While it may not be possible to completely avoid the impacts, they can be reduced. This paper provides an overview of the process taken in delivering a Wellington Lifelines Group report that demonstrates how impacts from a future major earthquake can be reduced through integrated and targeted infrastructure resilience investments. To quantify the benefits that can be achieved by making the proposed investments, impact modelling on nine different lifeline utilities in the Wellington metropolitan area were conducted; the assessment approach taken, and results derived and their use to prioritise resilience investments, are shown in this paper for selected key networks. The time-stamped service outage maps and tables produced from this work formed an essential input to evaluate and demonstrate the impact of the proposed resilience initiatives on the regional and national economies. [ABSTRACT FROM AUTHOR]

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. • We review - past coseismic coastal deformation on the Hikurangi subduction margin. • Along-margin temporal correlations are used to identify past subduction earthquakes. • Upper plate faults introduce uncertainty in earthquake source interpretation. • We identify ten possible subduction earthquakes in the past 7000 years. [ABSTRACT FROM AUTHOR]

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 sources and publication of the evidence has been somewhat fragmented. Here, we review physical evidence for past large to great earthquakes on the Alpine Fault to summarise current understanding, illustrate progress and highlight future directions. Paleoseismic evidence has been derived from tree disturbance, landscape features and trenches across the fault. These records have been supplemented and extended back in time with sedimentary evidence of Alpine Fault earthquakes from fault-proximal lakes and wetlands. In this review, we update radiocarbon analyses using recent calibration curves and modern Bayesian statistical methods where necessary to enable comparison between on-fault, fault-proximal and off-fault earthquake records. Over recent decades, Alpine Fault paleoseismology has progressed from playing an important role in demonstrating that large surface-rupturing earthquakes occur, to enabling estimates of earthquake recurrence behaviour, shaking intensities, rupture extents, landscape response durations and likelihood of the next earthquake. [ABSTRACT FROM AUTHOR]

The Manawahe Fault is located at the boundary between the tectonic Whakatane and the magmatic Okataina segments of the Taupō Rift. We investigate prehistoric ground surface fault ruptures and their timing in association with volcanic eruptions of the Okataina Volcanic Centre (OVC), using geomorphic fault mapping, paleoseismic trenching, ground penetrating radar and shallow drillcores. Paleoseismic trench data across the major strand shows that the Manawahe Fault ruptured at least seven times in the last c. 9.5 cal. ka (with a possible rupture 8 just prior to c. 9.5 cal. ka). At least four of these surface fault ruptures occurred during, or immediately prior to, volcanic eruptions. These eruptions, named Whakatane (c. 5.5 cal. ka – 1 fault rupture), Mamaku c.8 cal. ka −1 fault rupture), and the Rotoma (c. 9.5 cal. ka - 2-3 fault ruptures), were all sourced from the nearby Haroharo Volcanic Complex nested within the OVC, one of the two currently active volcanic lineaments within the OVC. Ground penetrating radar and drillcore data show that the Manawahe Fault has a slip rate of c. 3 mm/yr and that it only formed recently (< 26.5 ka ago), much more recently than the last caldera forming eruption, the c. 61 ka Rotoiti eruption. Fault rupture recurrence is 1580–2000 years. We discuss possible modes of ruptures of the Manawahe Fault in association with modes of volcanic unrest and magmatic processes; whether these prehistoric ruptures were seismogenic or not, and what the implications are for volcanic and seismic hazard. • Paleoseismic studies identify large prehistoric fault ruptures occur with volcanic eruptions. • Stress triggering between faults and volcanos is the most likely mode of interaction. • Fault slip rate in volcanic environments vary with evolution of nearby magmatic systems. • Large earthquakes triggered by volcanic eruptions need more consideration in seismic hazard. • Large earthquakes on nearby faults are underappreciated in volcanic hazard assessment. [ABSTRACT FROM AUTHOR]

Professional engineers have provided a range of inputs into the responses to the Canterbury Earthquake Sequence and the recovery process that has followed. This earthquake sequence has been unique in many respects, including the intensity of shaking produced in the Christchurch CBD by each of the major aftershocks in February, June and December 2011. For engineers, the heavy workload has been continuous from the response to the original 4 September 2010 Darfield earthquake, and will extend for several years to come. There have been many post-earthquake challenges for seismologists and geotechnical and structural engineers, commencing with urban search and rescue responses and rapid building evaluations, and extending through the more detailed assessments and repair specifications during the recovery phase. Engineers are required to interface with owners, regulatory authorities and insurers, and face many challenges in meeting the objectives of these different sectors, which are rarely aligned. Adding to the technical demands has been the requirement for many scientists and engineers to provide input into the Canterbury Earthquakes Royal Commission of Inquiry and other investigations. The Royal Commission was set up to investigate the failure of buildings that led to the loss of 185 lives in the 22 February 2011 aftershock, and has placed close scrutiny on many aspects of engineering activities, particularly those undertaken following the 4 September 2010 earthquake. The prominent public reporting of the Royal Commission hearings has placed additional pressure on many engineers, including those who volunteered their services following the original earthquake into a role for which they had received only limited prior training. Interpreting and communicating 'safety' in relation to the re-occupancy (or continued occupancy) of commercial buildings continues to be a challenge in the face of liability concerns. A more comprehensive understanding of the technical and process guidance required by engineers and authorities has resulted from the work undertaken in response to this earthquake sequence. Much of this guidance has now been produced, and will be of considerable benefit for future major earthquake events. This paper reflects on the range of work undertaken by scientists and engineers during the response and recovery stages. The scope and implications of the various official inquiries are summarised, and the potential impacts on engineers involved in the response to and recovery from future major earthquakes are briefly discussed. [ABSTRACT FROM AUTHOR]

Abstract: The sediment flux generated by postglacial channel incision has been calculated for the 2150 km2, non-glacial, Waipaoa catchment located on the tectonically active Hikurangi Margin, eastern North Island, New Zealand. Sediment production both at a sub-catchment scale and for the Waipaoa catchment as a whole was calculated by first using the tensioned spline method within ARC MAP to create an approximation of the aggradational Waipaoa-1 surface (contemporaneous with the Last Glacial Maximum), and second using grid calculator functions in the GIS to subtract the modern day surface from the Waipaoa-1 surface. The Waipaoa-1 surface was mapped using stereo aerial photography, and global positioning technology fixed the position of individual terrace remnants in the landscape. The recent discovery of Kawakawa Tephra within Waipaoa-1 aggradation gravels in this catchment demonstrates that aggradation was coincidental with or began before the deposition of this 22600 14C-year-old tephra and, using the stratigraphic relationship of Rerewhakaaitu Tephra, the end of aggradation is dated at ca 15000 14C years (ca 18000 cal. years BP). The construction of the Waipaoa-1 terrace is considered to be synchronous and broadly correlated with aggradation elsewhere in the North Island and northern South Island, indicating that aggradation ended at the same time over a wide area. Subsequent downcutting, a manifestation of base-level lowering following a switch to postglacial incision at the end of glacial-age aggradation, points to a significant Southern Hemisphere climatic warming occurring soon after ca 15000 14C years (ca 18000 cal. years BP) during the Older Dryas interval. Elevation differences between the Waipaoa-1 (c.15 ka) terrace and the level of maximum channel incision (i.e. before aggradation since the turn of the 20th century) suggest about 50% of the topographic relief within headwater reaches of the Waipaoa catchment has been formed in postglacial times. The postglacial sediment flux generated by channel incision from Waipaoa catchment is of the order of 9.5 km3, of which ~6.6 km3 is stored within the confines of the Poverty Bay floodplain. Thus, although the postglacial period represented a time of high terrigenous sediment generation and delivery, only ~30% of the sediment generated by channel incision from Waipaoa catchment probably reached the marine shelf and slope of the Hikurangi Margin during this time. The smaller adjacent Waimata catchment probably contributed an additional 2.6 km3 to the same depocentre to give a total postglacial sediment contribution to the shelf and beyond of ~5.5 km3. Sediment generated by postglacial channel incision represents only ~25% of the total sediment yield from this landscape with ~75% of the estimated volume of the postglacial storage offshore probably derived from hillslope erosion processes following base-level fall at times when sediment yield from these catchments exceeded storage. [Copyright &y& Elsevier]

Abstract: 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), 1000cal years BP and 1855AD. 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 500cal 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. [Copyright &y& Elsevier]

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 <100 km to the east of the Alpine Fault is possible. The role of tectonic block rotations in partitioning plate boundary deformation is less pronounced in the South Island compared to the North Island. Vertical axis rotation rates of tectonic blocks in the South Island are similar to that of the Pacific Plate, suggesting that edge forces dominate the block kinematics there. The southward migrating Chatham Rise exerts a major influence on the evolution of the New Zealand plate boundary; we discuss a model for the development of the Marlborough fault system and Hikurangi subduction zone in the context of this migration. [ABSTRACT FROM AUTHOR]

The authors discuss the study "Lidar reveals uniform Alpine fault offsets and bimodal plate boundary rupture behavior, New Zealand," by Gregory P. De Pascale, Mark C. Quigley and Tim R. H. Davies, published online on March 17, 2014 by "Geology." Topics addressed include the occurrence of partial fault ruptures in New Zealand's Alpine fault (AF) near Whataroa, the lack of evidence for bimodal rupture behavior, and the occurrence of moderate to large earthquakes in the historical record.