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The potential for future earthquakes on faults is often inferred from inversions of geodetically derived surface velocities for locking on faults using kinematic models such as block models. This can be challenging in complex deforming zones with many closely spaced faults or where deformation is not readily described with block motions. Furthermore, surface strain rates are more directly related to coupling on faults than surface velocities. We present a methodology for estimating slip deficit rate directly from strain rate and apply it to New Zealand for the purpose of incorporating geodetic data in the 2022 revision of the New Zealand National Seismic Hazard Model. The strain rate inversions imply slightly higher slip deficit rates than the preferred geologic slip rates on sections of the major strike‐slip systems including the Alpine Fault, the Marlborough Fault System and the northern part of the North Island Fault System. Slip deficit rates are significantly lower than even the lowest geologic estimates on some strike‐slip faults in the southern North Island Fault System near Wellington. Over the entire plate boundary, geodetic slip deficit rates are systematically higher than geologic slip rates for faults slipping less than one mm/yr but lower on average for faults with slip rates between about 5 and 25 mm/yr. We show that 70%–80% of the total strain rate field can be attributed to elastic strain due to fault coupling. The remaining 20%–30% shows systematic spatial patterns of strain rate style that is often consistent with local geologic style of faulting. Plain Language Summary: The potential for future earthquakes on faults is often inferred from velocities of the ground surface derived from satellite geodesy, but this approach can be challenging in complex deforming zones with many closely spaced faults. We present a new methodology for estimating the rate at which energy is accumulating on faults using measurements of surface strain rates. The method is applied to New Zealand for the purpose of incorporating geodetic data in the 2022 revision of the New Zealand National Seismic Hazard Model. We show that 70%–80% of the total deformation field can be attributed to energy accumulation on known active faults while the source of the remaining 20%–30% remains unknown. Along some of the major faults in New Zealand we find some important differences in rates of energy accumulation from what is expected from geologic data. Estimated rates are significantly lower than even the lowest geologic estimates on some faults in the fault system near highly‐populated Wellington. Key Points: We develop a method to invert geodetically derived strain rates for slip deficit rates on faultsWe find small but systematic differences between slip deficit rates and geologic slip ratesAbout 70%–80% of the surface strain can be attributed to elastic strain due to coupling on faults [ABSTRACT FROM AUTHOR]

The Hundalee Fault forms part of the southeastern margin of the 2016 Kaikōura Earthquake rupture zone. Its late Quaternary activity and structural character may offer insights to fault interrelationships associated with the 2016 rupture. Mapping of the Hundalee Fault revealed several pre-existing fault scarps. Trenching of a scarp across a fluvial terrace together with radiocarbon dating shows the occurrence of at least two, probably three, surface ruptures since 3.5 ka. The scarp records about 2.5 m of reverse-sense vertical deformation, mostly folding, of which ∼0.6 m occurred in 2016, along with subordinate sinistral slip. Fluvial terrace ages inferred from geomorphological relationships, together with the trenching results, indicate a long-term vertical slip rate of 0.2–0.4 mm/yr since at least 30 ka. Geological data indicate a relatively recently surface emergence of the Hundalee Fault from beneath a fault propagation fold. The 2016 Hundalee Fault rupture is interpreted as a break-out from an extensive blind thrust fault, whose motion triggered predominantly contractional rupture of an array of steeper near-surface faults. The thrust is hypothesised as having provided linkage in the 2016 rupture between the predominantly strike-slip ruptures of The Humps Fault to the southwest and the Kekerengu Fault to the northeast. [ABSTRACT FROM AUTHOR]

The Kaikōura Earthquake uplifted Kaikōura Peninsula by ≤∼1 m. Uplift in 2016 mainly resulted from slip on an offshore thrust fault (OSTF), modelled to splay from the plate-interface, and was further influenced by slip on two newly identified faults (Armers Beach Fault, ABF; Te Taumanu Fault, TTF) mapped onshore from differential lidar (D-lidar). Forward dislocation modelling indicates that 2016 peninsula uplift can be reproduced by mean slip of ∼2.3 m on the OSTF and 0.25–0.5 m on the ABF and TTF. The variable co-seismic uplift recorded during the 2016 earthquake differs from the near-uniform (1.2 ± 0.2°) northwest tilting of MIS5c (96 ± 5 ka) and MIS5e (123 ± 5 ka) marine terraces; these ages are constrained by Optically Stimulated Luminescence (OSL) dating and correlation to sea-level curves. Tilting of Late Quaternary marine terraces can be primarily reproduced by slip rates of ∼0.8–2.7 mm/yr on the OSTF and 0.3–0.6 mm/yr on the ABF. Slip on the TTF is not required to produce tilting of the marine terraces, suggesting that it may have ruptured less frequently than the OSTF and ABF in the Late Quaternary. The OSTF links 2016 ruptures north and south of Kaikōura, with the earthquake rupturing an interconnected network of faults. [ABSTRACT FROM AUTHOR]

The Mw 7.8 Kaikōura earthquake of November 14th, 2016 provided rare opportunities to evaluate ground deformation during a large strike-slip earthquake. Following the earthquake, both halves of a displaced paleoseismic trench were re-excavated and extended to test, refine, and extend the known late Holocene chronology of surface rupturing earthquakes on the Kekerengu Fault. 28 organic-bearing samples were collected during these excavations. Of these, six samples provided new 14C ages that could be superimposed on the preferred age model of (Little VDR, Kearse J, Norton K, Benson A, Wang N. 2018. Kekerengu fault, New Zealand: Timing and size of Late Holocene surface ruptures. Bulletin of the Seismological Society of America. 108(3B):1556–1572) to derive an expanded, updated age model of earthquake events on the fault that is now based on 16 dated samples. Including the 2016 earthquake, we recognise six surface rupturing earthquakes on the Kekerengu Fault since ∼2000 cal. B.P. Based on the last five events, our analysis yields an updated estimate of the mean recurrence interval for surface rupturing on the fault of 375 ± 32 yrs (1σ) since ∼1650 cal. B.P. An older, sixth event (E5) was not included in the preferred age model due to uncertainties in interpretation; however, incorporating this event into an alternative, six-event age model would adjust the recurrence interval estimate to 433 ± 22 yrs (1σ) since ∼2000 cal. B.P. [ABSTRACT FROM AUTHOR]

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]

Earthquake surface deformation provides key constraints on the geometry, kinematics, and displacements of fault rupture. However, deriving these characteristics from past earthquakes is complicated by insufficient knowledge of the pre‐event landscape and its post‐event modification. The 1987 Mw 6.5 Edgecumbe earthquake in the northern Taupō volcanic zone (TVZ) in New Zealand represents a moderate‐magnitude earthquake with distributed surface rupture that occurred before widespread high‐resolution topographic data were available. We use historical aerial photos to build pre‐ and post‐earthquake digital surface models (DSMs) using structure‐from‐motion techniques. We measured discrete and distributed deformation from differenced DSMs and compared the effectiveness of the technique to traditional field‐ and lidar‐based studies. We identified most fault traces recognized by 1987 field mapping, mapped newly identified traces, and made dense remote slip measurements with a vertical separation resolution of ∼0.3 m. Our maximum and average vertical separation measurements on the Edgecumbe fault trace (2.5 ± 0.3 and 1.2 m, respectively), are similar to field‐based values of 2.4 and 1.1 m, respectively. Importantly, this technique can discern between new and pre‐existing fault scarps better than field techniques or post‐earthquake lidar‐based measurements alone. Our surface displacement results are used to refine subsurface fault geometries and slip distributions at depth, which are further used to investigate potential magmatic‐tectonic stress interactions in the northern TVZ. Our results suggest the Edgecumbe fault dips more gently at depth than at the surface, hosted shallow slip in 1987, and may be advanced toward failure by interactions with nearby magma bodies. Plain Language Summary: Understanding earthquake behavior relies heavily on information about how past earthquakes changed the landscape. Detailed information about the surface topography before the earthquake is often limited, creating challenges for accurately measuring earthquake surface deformation. Aerial photos are widely available and can be used to create 3D digital surface models in places where other topographic information is lacking. We use historical aerial photos to make 3D datasets of the surface topography before and after the 1987 Edgecumbe earthquake in New Zealand. We calculated the difference between the two 3D datasets to identify and measure how the earthquake changed the landscape, and compared our results to previous measurements. We found that this method generally works as well as field methods for identifying and measuring fault movement, and has some advantages over other techniques. In particular, this approach can separate deformation from individual earthquakes, which had previously been a challenge. The results refine our understanding of the faults below the surface, provide insight into the earthquake's relationship to surrounding faults and volcanic systems, and allow us to better characterize seismic hazard both here and in other similar geologic settings. Key Points: Historical aerial photos can be used to generate pre‐ and post‐earthquake digital surface models for measuring displacementThis method performs at least as well as field surveys, and better captures single‐event displacements to constrain earthquake behaviorThe Edgecumbe earthquake is important for understanding low dip‐angle normal fault ruptures and possibly magma‐tectonic interactions [ABSTRACT FROM AUTHOR]

The complex 2016 MW 7.8 Kaikōura earthquake ruptured >20 faults and caused highly variable uplift and subsidence of an ~110 km stretch of coastline. The earthquake raised questions about fault interactions in regions of oblique convergence and especially subduction to strike-slip transition zones like the Kaikōura region. We integrate 2016 coastal vertical deformation observations with new mapping and dating of Holocene marine terraces to: (1) compare spatial patterns of 2016 coseismic and longer-term vertical motions, (2) investigate possible past multi-fault ruptures or temporal clusters of earthquakes around Kaikōura, and (3) assess the relative contributions of crustal faults and the Hikurangi subduction interface to late Holocene coastal uplift. We identify possible multi-fault ruptures or loose clusters of earthquakes at ca. 850–550 yr B.P. and ca. 350–100 yr B.P. Most (and possibly all) of the Kaikōura coast has been uplifted over the late Holocene; the 25-km-long Parikawa section of coast subsided coseismically in 2016 but appears to be uplifted through reverse slip on an offshore fault. Late Holocene uplift everywhere along the coastline of interest can be attributed to slip on known upper-plate faults; slip on a shallow-dipping (<20°) subduction interface cannot be ruled out but is not required to explain uplift. [ABSTRACT FROM AUTHOR]

Coseismic landslides are observed in higher concentrations around surface-rupturing faults. This observation has been attributed to a combination of stronger ground motions and increased rock mass damage closer to faults. Past work has shown it is difficult to separate the influences of rock mass damage from strong ground motions on landslide occurrence. We measured coseismic off-fault deformation (OFD) zone widths (treating them as a proxy for areas of more intense rock mass damage) using high-resolution, three-dimensional surface displacements from the 2016 Mw 7.8 Kaikōura earthquake in New Zealand. OFD zones vary in width from ~50 m to 1500 m over the ~180 km length of ruptures analyzed. Using landslide densities from a database of 29,557 Kaikōura landslides, we demonstrate that our OFD zone captures a higher density of coseismic landslide incidence than generic "distance to fault rupture" within ~650 m of surface fault ruptures. This result suggests that the effects of rock mass damage within OFD zones (including ground motions from trapped and amplified seismic waves) may contribute to near-fault coseismic landslide occurrence in addition to the influence of regional ground motions, which attenuate with distance from the fault. The OFD zone represents a new path toward understanding, and planning for, the distribution of coseismic landslides around surface fault ruptures. Inclusion of estimates of fault zone width may improve landslide susceptibility models and decrease landslide risk. [ABSTRACT FROM AUTHOR]

The glacio-fluvial sediments of the Whataroa Valley on the west coast of New Zealand's South Island contain a record of environmental change since the Last Glacial Maximum. The valley is cut by the Australia–Pacific plate-bounding Alpine Fault, the position of which is obscured by recent glacio-fluvial outwash deposits. Five seismic profiles collected across the inferred surface trace of the Alpine Fault between 2011 and 2018, using a variety of source types, are presented here; these profiles provide constraints on the fault's location in the upper few hundred metres of the near surface. The sedimentary strata in the Whataroa Valley have been classified into seismic facies based on their reflectivity characteristics. Two reflective seismic facies, recognisable in all profiles, have been interpreted to correspond to recent fluvial outwash gravels (seismic facies 1) and older post-glacial glaciofluvial or marine sediments (seismic facies 2). These reflective packages are cut by Alpine Fault rupture surfaces with reverse motion dips of 60° to 80° and total throw of up to 50 m. Faults imaged in three of the profiles are interpreted to correspond to the most recent surface rupture of the Alpine Fault, due to their close proximity to a recently trenched surface scarp. [ABSTRACT FROM AUTHOR]

The 2016 M w 7.8 Kaikoura, New Zealand, earthquake occurred along the eastern margin of the transition region between active subduction in the North Island and oblique collision in the South Island. To infer crustal properties, we imaged Q (1/seismic attenuation) by combining selected M > 3.5 aftershocks with data from previous Q models. For 158 distributed aftershocks, we fit spectral decay on temporary stations and all Geonet stations, providing 6194 t * p and 19 497 t * s. Considering the varied rheology and faults, we also used 2.5-D numerical models to study ductile strain development. The complex earthquake ruptured an ∼180-km-long zone of multiple faults, which involved jumping around the complicated eastern end of the Hope fault, without significant slip on the Hope fault. The Qs and Qp results show features in the upper and lower crust which correlate to the distribution and types of fault rupture. This earthquake involved numerous faults over a region of greywacke crust, where the underlying high Q Cretaceous slab is about 30-km depth. It initiated with ∼5-m slip on the Humps fault in a region of background seismicity and low Q lower crust, adjacent to the Hope fault. The central region near Kaikoura shows a high Q crustal block, which appears to have inhibited rupture; as the rupture progressed over several small faults to jump offshore of the apparently strong block. Underlying the Kaikoura greywacke crust, below 20-km depth, there is a 40-km-long region of increased Vp, Qs and gravity, which likely represents an intraplate plutonic complex emplaced into the Hikurangi Plateau, forming an elevated section which influences deformation. In the northern section, in a region with relatively uniform moderate to low Q , the earthquake evolved into the relatively continuous ∼80-km-long major rupture along the Jordan, Kekerengu and Needles faults, with ∼6–20 m dextral slip at depth and surface displacements of ∼10 m dextral and ∼2 m vertical. The northern progression of the rupture stopped when it approached an abrupt change to high Q crust across Cook Strait. At 20–30-km depth northwest of the rupture, deeper zones with low Q are consistent with regions of distributed ductile shear and creep where the observed afterslip may have occurred, where the underlying slab is 25–40 km deep. The numerical model shows that ductile deformation localizes in this area of lower crust above the relatively strong slab, connecting outer faults (Kekerengu) to inland faults (Clarence, Awatere, Wairau), and demonstrates that no subduction thrust is required under the Marlborough region. [ABSTRACT FROM AUTHOR]

To evaluate ground deformation resulting from large (~10 m) coseismic strike-slip displacements, we focus on deformation of the Kekerengu fault during the November 2016 Mw 7.8 Kaikōura earthquake in New Zealand. Combining post-earthquake field observations with analysis of high-resolution aerial photography and topographic models, we describe the structural geology and geomorphology of the rupture zone. During the earthquake, fissured pressure bulges ("mole tracks") initiated at stepovers between synthetic Riedel (R) faults. As slip accumulated, near-surface "rafts" of cohesive clay-rich sediment, bounded by R faults and capped by grassy turf, rotated about a vertical axis and were internally shortened, thus amplifying the bulges. The bulges are flanked by low-angle contractional faults that emplace the shortened mass of detached sediment outward over less-deformed ground. As slip accrued, turf rafts fragmented into blocks bounded by short secondary fractures striking at a high angle to the main fault trace that we interpret to have originated as antithetic Riedel (R') faults. Eventually these blocks were dispersed into strongly sheared earth and variably rotated. Along the fault, clockwise rotation of these turf rafts within the rupture zone averaged ~20°-30°, accommodating a finite shear strain of 1.0-1.5 and a distributed strike slip of ~3-4 m. On strike-slip parts of the fault, internal shortening of the rafts averaged 1-2 m parallel to the R faults and ~1 m perpendicular to the main fault trace. Driven by distortional rotation, this contraction of the rafts exceeds the magnitude of fault heave. Turf rafts on slightly transtensional segments of the fault were also bulged and shortened-relationships that can be explained by a kinematic model involving "deformable slats." In a paleoseismic trench cut perpendicular the fault, one would observe fissures, low-angle thrusts, and steeply dipping strike-slip faults-some cross-cutting one another-yet all may have formed during a single earthquake featuring a large strike-slip displacement. [ABSTRACT FROM AUTHOR]

Large earthquakes usually rupture plate boundary faults, releasing the accumulated stress as displacements localized along smooth, narrow faults. However, certain earthquakes initiate off main faults, rupturing adjacent, secondary faults. The mechanisms of such atypical stress release remain enigmatic, partly due to a lack of detailed geodetic evidence. Here using the 3D coseismic displacement field derived from space imaging geodesy, we detect 10‐km‐scale, nearly‐circular coseismic block rotation during the 2016 Mw 7.8 Kaikōura earthquake in New Zealand. Together, geodetic observations, longer term local paleomagnetic data, analytical, and discrete element modeling imply that localized block rotation occurred south of the Hope fault along weak, steep, bedding‐parallel boundaries within a narrow, ~20‐km‐wide dextral shear zone. That stress near plate boundary faults can be partially released in zones of distributed ruptures absorbing coseismic rotation may retard rupture along main faults. Our observations also suggest that coseismic rotation may help accomodate plate boundary propagation. Plain Language Summary: That the Mw 7.8, 2016, Kaikōura (New Zealand) earthquake, whose epicenter was near the Hope fault, did not rupture that fault which accommodates over half of the ~40 mm/year Pacific/Australian plate motion, is puzzling. Space‐borne radar images, that reveal fine details of the displacements within a 100‐km‐long and ~20‐km‐wide area south the Hope fault, show a clear pattern of clockwise block rotation bounded by three near‐orthogonal surface ruptures. Coseismic slips along the northern and southern edges of the block were ~2 m, a total close to the 5‐m slip accumulated since ~AD 1780 on the Hope fault. Crustal block rotation thus played a significant role in releasing accumulated strain, possibly preventing farther rupture propagation along that fault. Our geodetic observations and numerical modeling are in keeping with longer timescale paleomagnetic rotation along the same crustal shear zone, confirming the tight link between large seismic events and the broader tectonic regime. Key Points: Space imaging geodesy reveals coseismic block rotation during the 2016 Kaikōura earthquakeAnalytical and numerical modeling account for geodetic and local paleomagnetic evidence of clockwise rotationBlock‐rotation might have prevented rupturing on the Hope fault during the 2016 Kaikōura earthquake [ABSTRACT FROM AUTHOR]

In this study, we use version 2.0 of the digital inventory of landslides triggered by the MW 7.8 Kaikōura, New Zealand, earthquake of 14 November 2016 to revaluate some of the controls on their spatial distribution. Version 2.0 contains 29,557 hand-digitised landslides, whilst version 1.0 included only 10,195 mainly larger (> 10,000 m2) landslides. The main results from the re-analysis using version 2.0 of the inventory are the following: (1) the landslide frequency and density results indicate that the power laws fitted to version 1.0 and version 2.0 landslide inventories are similar; (2) the landslide densities decrease with increasing distance from the nearest fault that ruptured to the surface during the earthquake; (3) the larger landslides in the inventory occur on slopes with higher local slope relief; and (4) the results from logistic regression modelling using the version 2.0 inventory show that (a) the geological materials have a larger relative contribution to the fit of the overall model, when compared with the previous model based on the version 1.0 inventory, and (b) the "distance to fault" predictor variable continues to have more statistical power in predicting landslide probability than the modelled peak ground acceleration or peak ground velocity. These results suggest that future research on the Kaikōura earthquake landslide distribution—and the landslide distributions associated with other similar large earthquakes—might be directed towards investigating the interaction between surface fault rupture, fault damage-zone properties, earthquake-induced ground shaking, and the initiation of slope failures. [ABSTRACT FROM AUTHOR]

The Pāpaku Fault Zone, drilled at International Ocean Discovery Program (IODP) Site U1518, is an active splay fault in the frontal accretionary wedge of the Hikurangi Margin. In logging‐while‐drilling data, the 33‐m‐thick fault zone exhibits mixed modes of deformation associated with a trend of downward decreasing density, P‐wave velocity, and resistivity. Methane hydrate is observed from ~30 to 585 m below seafloor (mbsf), including within and surrounding the fault zone. Hydrate accumulations are vertically discontinuous and occur throughout the entire logged section at low to moderate saturation in silty and sandy centimeter‐thick layers. We argue that the hydrate distribution implies that the methane is not sourced from fluid flow along the fault but instead by local diffusion. This, combined with geophysical observations and geochemical measurements from Site U1518, suggests that the fault is not a focused migration pathway for deeply sourced fluids and that the near‐seafloor Pāpaku Fault Zone has little to no active fluid flow. Plain Language Summary: Faults are boundaries in the Earth where two different blocks of sediment or rock slide past each other. Offshore New Zealand, the Pāpaku Fault is very shallow and intersects the seafloor but connects to deeper faults kilometers below the seafloor where large earthquakes can occur. An ice‐like form of methane called hydrate also occurs within and surrounding the fault. We use scientific drilling data to understand the physical properties of the fault. Hydrate can affect fault properties and how fluid flows; however, based on the pattern of hydrate distribution and other geochemical and geophysical measurements, we suggest that the Pāpaku Fault does not have active fluid flow. Key Points: The Pāpaku Fault Zone is a 33‐m‐thick near‐seafloor splay fault drilled at Site U1518 on the Hikurangi MarginMultiple lines of observational, geophysical, and geochemical evidence suggest that there is little to no fluid flow along the Pāpaku Fault [ABSTRACT FROM AUTHOR]

Increasing displacement and strain accumulation in normal faults can result in the formation of hard-linked structures that are preferred loci for fluid leakage. Three-dimensional seismic data from offshore New Zealand reveals Miocene geological units that were structurally deformed to form several hard-linked fault zones. Fluids are observed to migrate through these breached zones into younger strata. Here, we use an automated approach by designing two different meta-attributes, the Thinned Fault (TFC) and Fluid (FC) Cubes, to capture the detailed geometry of hard-linked fault zones, and of fluid flowing through these same structures. The two meta-attributes are prepared through an amalgamation of different seismic attributes, which are trained based on the interpreter's skills and experience following a supervised scheme of neural learning. The meta-attributes enhance sub-surface geological features and reveal their structural geometries. Faults in the study area are therefore observed to strike to the NE with different geometries, e.g. forming curved shapes (F1 and F2), sigmoid shapes (F3), and Y shapes (F4). Relay ramps between these faults are intensively breached, allowing for important fluid migration through hard-linked structures. We demonstrate that our interpretation approach does not only honour the interpreter's knowledge about key geological processes, but also adds value in revealing the 3D architecture of hard-linked normal faults. Image 1 • A novel neural-network based automated fault interpretation is presented. • The amalgamated meta-attributes enhanced the imaging of subsurface geology. • Normal hard-linked fault zones and fluid migrated pathways are enhanced. • Fluid migration is enabled at breached hard-linked fault zones. [ABSTRACT FROM AUTHOR]

Actively deforming crust and upper mantle around the obliquely convergent Pacific-Australia plate boundary in the northern South Island of New Zealand have been investigated by seismic tomography using data from a temporary c. 50 station network plus GEONET. The Alpine-Wairau Fault (principal component of the plate boundary at the surface) transects the study area, separating the Buller-Nelson (BN) province of active compressional inversion involving steep reverse faulting to the northwest, from the Marlborough fault system (MA) dominated by dextral strike-slip faulting to the southeast. In the course of this study, MA hosted the 2013 Seddon earthquake sequence (M 5.9, 6.6) and the 2016 M 7.8 Kaikoura earthquake. Active fault structures and present seismicity are associated with a heterogeneous distribution of low-velocity and Vp/Vs anomalies. Elsewhere, there is a general association between crustal seismicity and low-velocity zones along major fault structures within both the MA and BN seismotectonic provinces along which high Vp/Vs anomalies are locally conspicuous. Areas of active crustal seismicity are also generally characterized by high Vp/Vs , for instance the hypocentre and aftershocks of the 2016 M 7.8 Kaikoura earthquake overlie a low-velocity region with high Vp/Vs. The coincidence of anomalously low Vp and Vs and anomalously high Vp/Vs with zones of high electrical conductivity defined by a previous MT transect is consistent with the notion that upward migration of overpressured hydrothermal fluid from the subducting slab at depth leads to a heterogeneous distribution of overpressured fluid in and around the base of the crustal seismogenic zone, weakening the overlying crust and promoting seismic rupture along major fault systems. It seems possible that the Association of mid-crustal low-velocity zones with anomalously high Vp/ Vs may diagnose rupture preparation zones where frictional strength is being lowered by the build-up of fluid overpressure concurrent with accumulating shear stress, so that eventual fault failure is 'dual-driven'. • Seismic low-velocity zones beneath both the Buller-Nelson inversion province and the Marlbourough fault system • Hypocenter of the 2016 Kaikoura earthquake within low velocity zone • Seismic low-velocity can be interpreted as fluid overpressured area. [ABSTRACT FROM AUTHOR]

Abstract Subduction systems globally terminate, allowing plate-motion to be transferred from the oceanic megathrust onto continental and/or oceanic transform faults. The mechanism of this kinematic transition over earthquake timescales is, however, poorly understood due to a lack of relevant data. Here, we study the 2016 M w 7.8 Kaikōura Earthquake in New Zealand, the first large instrumentally-recorded earthquake across a subduction-termination, to investigate this transfer mechanism in detail. We find that the Kaikōura Earthquake, unlike standard subduction earthquakes globally, involved a predominance (∼80%) of coseismic-slip on upper-plate faults and minor triggered-slip on the underlying oceanic subduction-thrust. In the months following the earthquake, the subduction-thrust accommodated most of the earthquake's afterslip down-dip of its co-seismic rupture zone. This top-down strain-release mechanism is in accord with local geological, geodetic and historical seismicity data which suggest that the bulk of plate-convergence (>75%) is accommodated in the upper-plate. We suggest, therefore, that this alternative strain-release mechanism, which is distinct from standard plate-boundary earthquakes, is characteristic of subduction-terminations and results in the majority of seismic/tsunami hazard being on steep near-surface faults. Highlights • The first large instrumental earthquake to have ruptured a subduction termination. • Primary slip on upper-plate faults triggers minor slip on the subduction-thrust. • Afterslip on the plate-interface released down-dip of the co-seismic asperities. • Plate-interface and offshore splay-fault key elements in transferring coseismic slip. • A top-down strain-release mechanism may typify subduction-terminations globally. [ABSTRACT FROM AUTHOR]

The 2016 Kaikoura, New Zealand, earthquake was one of the most complex ruptures ever recorded. The epicentre was located well inland, but the rupture area extended offshore and generated a modest tsunami which was recorded by tide gauges. Here, we present a detailed estimate of seafloor vertical displacement during the earthquake sequence by a joint inversion of tsunami waveforms and vertical displacement data observed at GPS stations and obtained by field surveys. The combined dataset provides a solution with good resolution, capable of resolving test sources of 20 km of characteristic diameter throughout the study area. We found two seafloor uplift regions which are located very close to the coast, one is located offshore of the Kaikoura peninsula and the other larger uplift region is located near the Kekerengu and Needles faults. To estimate crustal deformation with a complete spatial coverage of the event, the estimated seafloor vertical displacement was combined with the inland vertical displacement from InSAR and GPS datasets. This vertical displacement is then inverted for the fault slip distributions of the Needles, Jordan-Kekerengu, Papatea, Hundalee, Hump faults, and a newly identified fault beneath Kaikoura. We also found that the Needles fault is probably an offshore extension of the Kekerengu fault. The seismic moment calculated from the fault slip distributions by assuming a rigidity of 2.7 × 1010 N/m2, is 5.19 × 1020 Nm or equivalent to Mw 7.8. This total seismic moment estimate is consistent with that of the Global Centroid Moment Tensor solution. The tsunami potential energy calculated from the seafloor vertical displacement is 9.40 × 1012 J, of which about 70% is attributed to movement on the faults known to have ruptured, suggesting a secondary source for tsunami generation. [ABSTRACT FROM AUTHOR]

• Point pattern analyses applied to thermal anomalies of a geothermal area. • From which shallow permeability and heat movement are inferred. • Two broad regions can be identified which present distinct subsurface conditions. Geothermal areas are studied with a diversity of techniques, including remote sensing (e.g. hyperspectral and thermal imagery) which can provide a time and cost efficient method to assess the surface of geothermal areas and infer subsurface processes. This study presents the analysis of thermal anomalies extracted from a single thermal infrared image covering Waiotapu Geothermal Field, New Zealand. Point pattern analyses were undertaken to assess any dominant orientations, and departures from randomness based on anomaly locations. The thermal anomalies present orientations that approximately align with nearby active faults, suggesting fault control in the Waiotapu Geothermal Field. Two distinct regions were observed, northern areas and southern areas. Northern areas show higher temperatures (i.e. >47 C°) and lower densities of thermal anomalies, with an orientation close to that of the whole field (∼ N22E°) and separation within cluster separations of ∼250 m, signalling to a high content of clays and proximity to the heat source. Southern areas exhibit lower temperatures (i.e. <47 C°) and a higher density of clustered thermal anomalies in a variety of orientations with clustering at all distances, indicating higher permeability at shallow depths. This is likely caused by a thinner litho-cap layer and a history of hydrothermal eruptions and collapse craters. Thermal imagery can therefore be used to infer the subsurface processes taking place at geothermal areas, elucidating information about the shallow permeability and heat movement. Our method can be applied to any other geothermal field for exploration to understand the shallow substrate and its control on porosity and permeability structure. [ABSTRACT FROM AUTHOR]

On 2016 November 13, an Mw 7.8 earthquake occurred in the northeast of the South Island of New Zealand near Kaikoura. The earthquake caused severe damages and great impacts on local nature and society. Referring to the tectonic environment and defined active faults, the field investigation and geodetic evidence reveal that at least 12 fault sections ruptured in the earthquake, and the focal mechanism is one of the most complicated in historical earthquakes. On account of the complexity of the source rupture, we propose a multisegment fault model based on the distribution of surface ruptures and active tectonics. We derive the source rupture process of the earthquake using the kinematic waveform inversion method with the multisegment fault model from strong-motion data of 21 stations (0.05-0.35 Hz). The inversion result suggests the rupture initiates in the epicentral area near the Humps fault, and then propagates northeastward along several faults, until the offshore Needles fault. The Mw 7.8 event is a mixture of right-lateral strike and reverse slip, and the maximum slip is approximately 19 m. The synthetic waveforms reproduce the characteristics of the observed ones well. In addition, we synthesize the coseismic offsets distribution of the ruptured region from the slips of upper subfaults in the fault model, which is roughly consistent with the surface breaks observed in the field survey. [ABSTRACT FROM AUTHOR]

The distribution of slip during an earthquake and how it propagates among faults in the subduction system play a major role in seismic and tsunami hazards, yet they are poorly understood because offshore observations are often lacking. Here we derive the slip distribution and rupture evolution during the 2016 M w 7.9 Kaikōura (New Zealand) earthquake that reconcile the surface rupture, space geodetic measurements, seismological and tsunami waveform records. We use twelve fault segments, with eleven in the crust and one on the megathrust interface, to model the geodetic data and match the major features of the complex surface ruptures. Our modeling result indicates that a large portion of the moment is distributed on the subduction interface, making a significant contribution to the far field surface deformation and teleseismic body waves. The inclusion of local strong motion and teleseismic waveform data in the joint inversion reveals a unilateral rupture towards northeast with a relatively low averaged rupture speed of ∼1.5 km/s. The first 30 s of the rupture took place on the crustal faults with oblique slip motion and jumped between fault segments that have large differences in strike and dip. The peak moment release occurred at ∼65 s, corresponding to simultaneous rupture of both plate interface and the overlying splay faults with rake angle changes progressively from thrust to strike-slip. The slip on the Papatea fault produced more than 2 m of offshore uplift, making a major contribution to the tsunami at the Kaikōura station, while the northeastern end of the rupture can explain the main features at the Wellington station. Our inversions and simulations illuminate complex up-dip rupture behavior that should be taken into consideration in both seismic and tsunami hazard assessment. The extreme complex rupture behavior also brings new challenges to the earthquake dynamic simulations and understanding the physics of earthquakes. [ABSTRACT FROM AUTHOR]

The M7.8 Kaikoura Earthquake that struck the northeastern South Island, New Zealand, on November 14, 2016 (local time), is one of the largest ever instrumentally recorded earthquakes in New Zealand. It occurred at the southern termination of the Hikurangi subduction margin, where the subducting Pacific Plate transitions into the dextral Alpine transform fault. The earthquake produced significant distributed uplift along the north-eastern part of the South Island, reaching a peak amplitude of ∼8 m, which was accompanied by large (≥10 m) horizontal coseismic displacements at the ground surface along discrete active faults. The seismic waveforms' expression of the main shock indicate a complex rupture process. Early automated centroid moment tensor solutions indicated a strong non-double-couple term, which supports a complex rupture involving multiple faults. The hypocentral distribution of aftershocks, which appears diffuse over a broad region, clusters spatially along lineaments with different orientations. A key question of global interest is to shed light on the mechanism with which such a complex rupture occurred, and whether the underlying plate-interface was involved in the rupture. The consequences for seismic hazard of such a distributed, shallow faulting is important to be assessed. We perform a broad seismological analysis, combining regional and teleseismic seismograms, GPS and InSAR, to determine the rupture process of the main shock and moment tensors of 118 aftershocks down to Mw 4.2. The joint interpretation of the main rupture and aftershock sequence allow reconstruction of the geometry, and suggests sequential activation and slip distribution on at least three major active fault domains. We find that the rupture nucleated as a weak strike-slip event along the Humps Fault, which progressively propagated northward onto a shallow reverse fault, where most of the seismic moment was released, before it triggered slip on a second set of strike-slip faults at the northern end of the rupture. The northern and southern strike-slip fault domains have the same orientation but are spatially separated by >15 km. In our model, the low angle splay thrust fault is located above the slab and connects the strike-slip faults kinematically. During the aftershock phase, the entire fault system remained active. [ABSTRACT FROM AUTHOR]

The 2016 M 7.8 Kaikōura earthquake was one of the largest earthquakes in New Zealand's historical record, and it generated the most significant local source tsunami to affect New Zealand since 1947. There are many unusual features of this earthquake from a tsunami perspective: the epicentre was well inland of the coast, multiple faults were involved in the rupture, and the greatest tsunami damage to residential property was far from the source. In this paper, we summarise the tectonic setting and the historical and geological evidence for past tsunamis on this coast, then present tsunami tide gauge and runup field observations of the tsunami that followed the Kaikōura earthquake. For the size of the tsunami, as inferred from the measured heights, the impact of this event was relatively modest, and we discuss the reasons for this which include: the state of the tide at the time of the earthquake, the degree of co-seismic uplift, and the nature of the coastal environment in the tsunami source region. [ABSTRACT FROM AUTHOR]

The Alpine Fault is inferred on paleoseismological grounds to produce magnitude 8 earthquakes approximately every 330 yrs and to have last ruptured almost 300 yrs ago in 1717 AD. Despite approximately 90% of its typical interseismic period having elapsed since the last major earthquake, the Alpine Fault exhibits little present-day microseismicity and no geodetic evidence for shallow creep. Determining the mechanical state of the fault ahead of a future earthquake is a key objective of several studies, including the Deep Fault Drilling Project (DFDP). Here we use a network of borehole seismometers installed in conjunction with DFDP to detect and characterise low-magnitude seismicity adjacent to the central section of the Alpine Fault. We employ matched-filter detection techniques, automated cross-correlation phase picking, and singular value decomposition-derived magnitude estimation to construct a high-precision catalogue of 283 earthquakes within 5 km of the fault trace in an otherwise seismically quiet zone. The newly recognised seismicity occurs in non-repeating, spatially and temporally limited sequences, similar to sequences previously documented using standard methods but at significantly lower magnitudes of M L < 1.8 . These earthquakes are not clustered on a single distinctive structure, and we infer that they are distributed throughout a highly fractured zone surrounding the Alpine Fault. Focal mechanisms computed for 13 earthquakes using manual polarity picks exhibit predominantly strike-slip faulting, consistent with focal mechanisms observed further from the fault. We conclude that the Alpine Fault is locked and accumulating strain throughout the seismogenic zone at this location. [ABSTRACT FROM AUTHOR]

Relative to more mature fault zones, immature fault zones that have accumulated smaller total displacement are characterized by less efficient strain localization and more complicated earthquake ruptures. How differences in maturation are reflected in regional-scale upper-crustal fracturing is not well known. Recently, complicated earthquake ruptures associated with immature fault zones, such as the 2016 Kaikōura earthquake in New Zealand, have occurred in areas that are in regional proximity (<100 km away) to more mature faults. Here we examine whether inefficient strain localization in less mature fault zones is associated with a broader distribution and anomalously elevated concentration of fractures over distances of tens of kilometers. We use regional seismic arrival-time tomography in a broad area around the Kaikōura earthquake to investigate lateral variations in Vp and Vp/Vs. Focusing on the extensively faulted but compositionally uniform Torlesse-Pahau terrane in the Marlborough region where the earthquake occurred, we attribute lateral variations in Vp and Vp/Vs to differences in concentration of fluid-filled fractures. Using numerical models relating seismic velocities and fracturing, we solve for the lateral variation in concentration of ∼0.01 aspect ratio fluid-filled fractures. We find that areas near the Kaikōura rupture have >3% elevated fracture porosity compared to the adjacent area to the north. The elevated regional fracturing in the Kaikōura area is interpreted to result from more distributed deformation, and broader distribution of earthquakes, due to inefficient localization of strain from a regionally uniform strain rate field, highlighting the relationship between relative maturity of upper-crustal fault zones and lateral variability of regional upper-crustal properties. Plain language summary: When earthquakes occur in immature fault zones (areas that have accumulated small total displacement), they tend to rupture multiple poorly developed faults of diverse orientations. In contrast, more mature fault zones are associated with more developed, smoother faults and more localized earthquake activity. How these differences in maturation are reflected in the regional distribution of fractures is not well known. Here we use the arrival times of P and S waves from earthquakes to constrain seismic velocities (Vp and Vp/Vs) and use numerical models to relate seismic velocities to fracture concentration. We focus on the Marlborough region of the South Island, New Zealand, where immature fault zones recently ruptured during the 2016 Kaikōura earthquake but which also has more mature fault zones <100 km away. We find elevated fracture concentrations (3% higher fracture porosity), indicative of more distributed deformation along immature fault zones relative to more mature fault zones. In immature settings, fracturing is not as effectively localized along individual fault traces, leading to a broadly distributed fracture network. • We image upper-crustal Vp and Vp/Vs, and interpret their variations in terms of amount of fluid-filled fractures. • The Marlborough region, which experiences near-uniform shear, has variable fluid-filled fracture concentration. • Within the Marlborough region, areas of less mature faulting have more fluid-filled fractures than more mature areas. [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 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]

Understanding the seismic hazard posed by large earthquakes requires paleoseismic investigation because most faults have not ruptured repeatedly during the period of historic records. However, determining the location and length of fault ruptures using paleoseismic data remains challenging. Our study demonstrates that lake sediments record the high intensity shaking that occurs proximal to fault rupture, allowing the location and length of ruptures to be reconstructed. In two lakes adjacent to the Alpine Fault, New Zealand, seismic shaking is recorded as subaqueous mass-wasting derived turbidites formed by coseismic subaqueous slope failures, which are overlain by sets of hyperpycnites representing elevated fluvial sediment fluxes from earthquake-induced landslides. Precise radiocarbon age models show that shaking events are synchronous between the two lake sites and correlate with the timing of known Alpine Fault earthquakes. Modelled shaking intensities for the last two Alpine Fault earthquakes show that subaqueous mass-wasting occurs when shaking intensities exceed Modified Mercalli scale (MM) VI–VII, and that fluvial sediment fluxes from earthquake-induced landslides occur when shaking intensities exceed MM IX. The data demonstrate that lake records distinguish between strong (MM VI) and violent (MM IX) shaking at a lake site. The ability to map the spatial extent of MM IX shaking provides new insights into the timing and extent of rupture for the last five earthquakes on the Alpine Fault. The study demonstrates that lake deposits constrain the spatial extent of rupture during large earthquakes and may yield long records of the spatial and temporal patterns of fault rupture. [ABSTRACT FROM AUTHOR]

High-resolution airborne LiDAR and field mapping were used to investigate a 29 km-long section of the Hurunui segment of the Hope Fault concealed beneath beech forest. Approximately 20 km of the dextral strike-slip principal slip zone (PSZ) was identified as a series of 69 individual fault strands on the LiDAR DEM. Mapping revealed 70 normal, 55 dextral-reverse, and 100 secondary faults, many of which were previously unrecognized. Secondary faults are kinematically linked with the PSZ and comprise a complex surface fault deformation zone (FDZ). A Rose diagram weighted by the lengths of the PSZ strands shows that the Hurunui segment strikes between 070° and 075° and is optimally oriented for dextral strike-slip within the regional stress field. The observed fault zone complexity is thus unlikely to result from large-scale fault mis-orientation with respect to regional stresses. FDZ width measurements from 415 locations reveal a spatially-variable, active FDZ up to ~ 500 m wide with an average width of 200 m. FDZ width increases with increased hanging wall topography and increased topographic relief (e.g., adjacent to high topography with deeply incised streams), suggesting that along-strike topographic perturbations to fault geometry and stress states increase fault zone complexity and width. Where adjacent PSZ strands strike between 070° and 075°, the FDZ is ≤ 150 m wide, however, FDZ width increases where the tips of adjacent PSZ segments locally vary in strike by ≥ 10°. FDZ width and surface fracture density also appear to increase with increasing thickness of alluvial deposits overlying bedrock. Our results indicate that spatial variations in near-fault topography and geology can generate along-strike variability in the morphology of surface ruptures, even in the case of fast-slipping, structurally mature faults where more confined, simplistic ruptures are expected at seismogenic depths. [ABSTRACT FROM AUTHOR]

The 1848 and 1855 earthquakes provide examples of clustered earthquake sequences involving several faults. Historical evidence indicates that fault rupturing and ground deformation on both sides of Cook Strait occurred over periods of several days during the October 1848 earthquakes on the Awatere, Ohariu and possibly the Wellington faults, with shallowing in Lambton Harbour, Wellington. The January–February 1855 earthquakes occurred on the Wairarapa, Wharekauhau, Nicholson Bank, Vernon, Awatere and Needles faults. The pattern of faulting suggests the existence of distinct seismogenic zones across Cook Strait, within which mainshock triggering of aftershock displacement on major faults can occur. [ABSTRACT FROM PUBLISHER]

Gas hydrates are widespread along convergent margins, but their distribution is highly variable. This variability has been attributed to a range of factors, such as the source of gas and the occurrence of permeable faults and porous or fractured reservoirs. We test these concepts on the Hikurangi Margin, where gas hydrate occurrences of variable character are well-documented by seismic reflection datasets and scientific drilling. We use 3D gas hydrate systems modelling to reconstruct processes of gas generation, migration and gas hydrate formation through time in two thrust ridges at the deformation front (Glendhu and Honeycomb ridges). We compare the results of scenarios using different fault and rock properties with indications for concentrated gas hydrates in reflection seismic data. Gas hydrate distributions are best reproduced by models predicting focussed gas migration through thrust faults and permeable strata. The gas is predominantly sourced from microbial generation beneath the gas hydrate stability zone (HSZ) in sedimentary troughs adjacent to the ridges and migrates up-dip as free gas. During progressive ridge deformation, gas generation shifts to the landward side of the ridges, where strata are rapidly buried, while erosion occurs at the crest of the ridges. A prominent back-thrust in the structurally more mature Glendhu Ridge diverts migrating gas into the HSZ and leads to preferential gas hydrate formation in the landward side of the ridge. Recycling of gas at the base of the HSZ during the past 2 Myrs led to an enrichment of gas hydrates, first in the center of the anticlines and then progressively more in the landward limbs. We propose that this process of diverting gas migration into the HSZ during thrust ridge formation is a common feature not only at the southern Hikurangi Margin, but in many convergent margins with high sedimentation rates and a thick accretionary wedge. • Gas hydrate systems modelling reproduces concentrated gas hydrates indicated by high amplitude seismic reflections. • Spatially variable rates in microbial gas generation beneath the hydrate stability zone drive gas hydrate formation. • Gas migration through faults and up-dip migration through permeable layers control gas hydrate distribution within ridges. • Gas hydrate accumulation is enhanced by gas recycling, leading to the formation of concentrated gas hydrates in <2 Ma. [ABSTRACT FROM AUTHOR]

The September 2010 Mw 7.1 Darfield (Canterbury) earthquake in New Zealand is one of the best-recorded earthquakes of this magnitude. The earthquake occurred on a previously unidentified fault system and generated a 29.5 ± 0.5-km-long surface rupture across a low-relief agricultural landscape. High-accuracy measurements of coseismic displacements were obtained at over 100 localities along the Greendale fault. Maximum net displacement (Dmax) (5.3 ± 0.5 m) and average net displacement (Davg) (2.5 ± 0.1 m) are anomalously large for an earthquake of this Mw. Dmax / surface rupture length (SRL) and Davg/SRL ratios are among the largest ever recorded for a continental strike-slip earthquake. "Geologically derived" estimates of moment magnitude (Due to image rights restrictions, multiple line equation(s) cannot be graphically displayed) are less than the seismologically derived Mw, derived using widely employed SRL-Mw scaling regressions. Due to image rights restrictions, multiple line equation(s) cannot be graphically displayed is greater than Mw using Dmax- and Davg-Mw regressions. The "geologically derived" static stress drop of 13.9 ± 3.7 MPa provides a context with which to compare this earthquake rupture to interplate and intraplate ruptures of similar Mw. This data set provides fundamental information on fault rupture processes relevant to seismic-hazard modeling in this region and analogous settings globally. [ABSTRACT FROM AUTHOR]

The article discusses a study on the temporal associations between single volcanic eruptions from Okataina volcanic center (OVC) and normal fault ruptures in the northern sector of the Taupo rift in New Zealand. The researchers examined evidence for volcano-tectonic interactions. They reviewed the eruptive history of the OVC. They found associations between the timing of fall tephra on the fault scarp. They also observed that ruptures have no relationship with tephra deposition.

The paleoseismic research aims to document earth activity during earthquakes, such as displacements of fault, rupture location, distribution of slip or ground shaking intensity. The earthquakes are usually distributed on the plate boundaries causing big damages of life on the Earth. Four faults in North America, New Zealand and Europe with different behaviour, direction and sense of movement have been chosen to document the seismic activity within the world. The White Creek Fault, the Greendale Fault, the San Andreas Fault and the Paganica Fault have been responsible for the earthquakes of M > 6 in the last century. Figures in this paper show the evidence of the earthquakes that can be visible in the field. [ABSTRACT FROM AUTHOR]

The middle Clarence valley, or eastern, section of the active Clarence Fault bounds the steep southeast flank of the Inland Kaikoura Range, Marlborough, New Zealand. This section of the fault extends c. 45 km northeastwards from its junction with the Elliott Fault to Mead Stream, where the active trace of the fault appears to abruptly end. Along the active trace, 41 separate right-lateral offsets of c. 3-40 m were recorded with uncertainties of 10-50% (mean 25%) using tape measurement of displaced topographic features (e.g., gully walls, landslide margins, and ridge crests). Single-event right-lateral displacements of 7 ± 2 m are inferred and indicate earthquake magnitudes of Mw 7.2-7.9. Probable rupture lengths have been in excess of 45 km, which suggests that rupture of the middle Clarence valley (eastern) section of the fault extended to the west onto the central Clarence and/or Elliott Faults. Stream incision through the uphill-facing fault scarp at Ravine Stream and Dead Horse Gully has exposed progressively faulted peat and charcoal horizons. Elsewhere, there are several exposures of unfaulted sediments. Twelve radiocarbon samples dated from these horizons constrain the timing of the four most recent surface-rupture earthquakes on the Clarence Fault in the study area. The most recent surface rupture took place at c. 1700-1900 cal. yr BP (rounded to the nearest hundred years), with two surface ruptures since c. 3400 cal. yr BP, three since 6700 cal. yr BP, and most likely a fourth surface rupture at c. 6600-6900 cal. yr BP. These data suggest a recurrence interval for surface-rupture earthquakes of c. 1700 yr, and imply a lateral slip rate of c. 4 mm/yr (i.e., c. 7 m of slip every c. 1700 yr). [ABSTRACT FROM AUTHOR]

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 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]

New mapping of the Martinborough Fault utilising high resolution LIDAR data and orthophotos defines a c. 1.3 km long active fold trace consisting of a broad (50-150 m wide) warp crossing dissected alluvial fans. GPS survey profiles across the fold-scarp reveal vertical separations ranging from 1.2 to 6 m on two fan surfaces. Published OSL ages imply a Porewan age for the upper fan (surface age c. 55 ka). We calculate a revised vertical slip rate of c. 0.1 mm/yr (previously published rates range between 0.3 and 0.67 mm/yr) and a recurrence interval of c. 15 000 yr from these new data. This places the fault within the Ministry for the Environment Active Fault Guidelines Recurrence Interval Class V (>10 000 to ≤20 000 yr), to which a medium level of confidence is assigned. [ABSTRACT FROM AUTHOR]

Laser-ablation 40Ar/39Ar step-heating analyses of 20 pseudotachylyte veins from a single location along the exhumed central portion of the active Alpine fault of New Zealand yield total gas age values between 1 and 19 Ma. Evidence shows that they are genetically related and were formed during coeval episodes of seismogenic melting at shallow crustal depth, contrasting with a spread in formation ages. The total gas ages show an exponential decrease with increasing proportion of melt matrix and K content, reflecting incomplete degassing and mixtures of radiogenic Ar sources. Calculation of intercepts for all-melted matrix and all-clast end-member components indicate ca. 570 ka (Quaternary) friction-melting ages of ca. 332 Ma (Lower Carboniferous) source rock. Assuming an average exhumation rate of 6–9 mm/yr for uplift and erosion, these results imply that friction melts were generated during major slip episodes at ∼3.5–5 km crustal depth. We conclude that reliable dating of young pseudotachylyte can be accomplished by combining chronologic study with clast-matrix quantification of genetically related vein assemblages. [ABSTRACT FROM AUTHOR]

The article examines the effect of a tsunami on the coastal margin of the South Island, New Zealand. The researchers implemented a numerical model, which was based on the Reynolds-averaged Navier-Stokes (RANS) equation to calculate runup and inundation arising from locally-generated tsunami along the coast. Based on the results, the different generation events had significant effects on different parts of the coastal margin where the study area was very exposed to damage from a fault rupture.

This study aims to understand the process behind the worldwide connection between deep crustal/upper mantle earthquakes and CO 2 emissions along faults in rift zones. We do this by studying CO 2 -induced mineral reactions that facilitate strain localization in peridotites from an ancient rift zone in the Seiland Igneous Province (SIP), North Norway. Strain localization in association with hydration processes is well documented in all types of tectonic settings and has major implications for rheological behavior in active plate margin processes. The implications of CO 2 -bearing fluids are less studied, though experiments have shown how CO 2 can influence the flow laws of olivine by imposing a brittle and more localized type of deformation. This study documents narrow shear zones observed within ultramafic rocks from the Seiland Igneous Province (SIP) comprising large volumes (>20,000 km3) of mafic, ultramafic, silicic and alkaline melts that were emplaced into the lower continental crust (25–30 km) between 570 and 560 Ma under an extensional regime. The extensional shear zones are mm cm-scale and contain extremely fine-grained material with a distinct shape preferred orientation (SPO), but weak to absent crystallographic preferred orientation. The shear zones offset dykes across numerous micro-faults that are documented in areas close to a major fault zone cutting through the area. Within the shear zones, olivine and clinopyroxene react to form orthopyroxene and dolomite at approximately 11 kb and 850 °C according to the reaction: 2 Olivine + Clinopyroxene + 2 CO 2 = Dolomite + 2 Orthopyroxene This reaction formed coronas of orthopyroxene and dolomite between olivine and clinopyroxene in the shear zones. In addition, large olivine grains proximal to the shear zones show a microfabric with subgrain walls decorated by rounded grains of dolomite and more irregular and elongated grains of orthopyroxene. Clinopyroxene grains are separated from the enstatite and dolomite by at least hundreds of microns, suggesting material transport within the shear zone. The shear zones thus provide a unique insight into the interplay between CO 2 -metasomatism and reaction accommodated strain softening. Carbonation-driven cracking and mineral reaction also serves to reduce grain size, making grain boundary sliding an efficient process, further enhancing the rheological contrast between the shear zone and the host rock. The sudden decrease in rock strength could lead to rapid deformation and triggered pseudotachylite formation during earthquake events in the near proximity of the micro-shear zones. Our observations match the relations between CO 2 emissions and earthquakes observed in present rift environments such as the East African rift and in New Zealand, and underline the importance of active shear zones as fluid conduits in the lower crust and upper mantle. • Mantle CO 2 facilitates brittle fracturing of olivine in deep crust/mantle. • Reinfjord as an analogue for understanding the source of deep tremors observed in the East African Rift. • Evidence of earthquake processes underneath present continental rift zones. [ABSTRACT FROM AUTHOR]

The article offers information on the new study on earthquakes conducted after the magnitude-7.8 Kaikoura earthquake struck New Zealand on November 14, 2016 causing ruptures on twelve different faults that earlier were believed to be independent. It talks of seismologists upgrading the likelihood of larger compound quakes due to gaps and ruptures found in faults. Scientists are trying to understand how unconnected faults as far as fifteen kilometers ruptured together in the Kaikoura earthquake.

The real-time retrieval of highly accurate seismic waveforms is essential for the earthquake early warning and fault rupture process inversion. Although the traditional strong motion(SM) sensor can record seismic waveforms with very high accuracy and frequency, it suffers from baseline errors due to the tilt or rotation of the instrument. Compared with the SM, the High-rate GNSS can record ground displacements directly without drift. But it has higher noise and lower sampling rate than that of SM. To complement the advantages of High-rate GNSS and SM, the PPP-based tight integration methods of two sensors have been proposed in the past few years. However, limited by the precise orbit and clock products, it is not possible for traditional PPP to record seismic waveforms in real time. In April 2013, the international GNSS service(IGS) issued the real-time service(RTS), which makes the real-time tight integration of High-rate GNSS and strong motion records possible. Therefore, based on the IGS RTS products, we analyzed the performance of the real-time PPP-based tight integration of two sensors using co-located records collected during the 2016 Mw 7.8 earthquake in New Zealand and 2016 Mw 6.5 earthquake in central Italy in a simulated real-time mode. The results show that the real-time combined displacements include more abundant seismic signals without clipping and drift if the baseline shift is estimated as a random walk process, and the RMSE(Root Mean Square Error) in the North, East and Up component is 3mm, 3mm and 6mm separately while taking post combined displacements as a reference. [ABSTRACT FROM AUTHOR]

Laboratory experiments on serpentinite suggest that extreme dynamic weakening at earthquake slip rates is accompanied by amorphisation, dehydration and possible melting. However, hypotheses arising from experiments remain untested in nature, because earthquake ruptures have not previously been recognised in serpentinite shear zones.We document the progressive formation of high-temperature reaction products that formed by coseismic amorphisation and dehydration in a plate boundary-scale serpentinite shear zone. Magnetite-coated slip surfaces within the serpentinite mélange of the Livingstone Fault, New Zealand, contain microstructural and mineralogical evidence for coseismic dehydration and amorphisation of serpentinite due to frictional heating. Directly adjacent to the principle slip surface are encapsulated the highest-temperature products of serpentinite dehydration consisting of aggregates of nanocrystalline olivine and enstatite, indicating minimum peak coseismic temperatures of ca. 925 ± 60 °C. Further from the slip surface, nanocrystalline olivine co-exists with talc, grading into amorphous and poorly-crystalline material. Below the magnetite layer, no products of dehydration or amorphisation are identifiable. Finite element modelling suggests that frictional heating during earthquakes of magnitude 2.7–4 can satisfy the petrological constraints on the coseismic temperature profile, assuming that coseismic fluid storage capacity and permeability are increased by the development of reaction-enhanced porosity. Our results indicate that earthquake ruptures can propagate through serpentinite shear zones, and that the signatures of transient frictional heating can be preserved in the fault rock record. [ABSTRACT FROM AUTHOR]

A response is presented from the authors of the study "Lidar reveals uniform Alpine fault offsets and bimodal plate boundary rupture behavior, New Zealand," published online on March 17, 2014 by "Geology." Topics discussed include indicators of surface faulting that influence the extent and timing of Alpine fault (AF) paleo-earthquakes along New Zealand's plate boundary AF, the inability of models of full AF ruptures to satisfactorily explain paleoseismic records, and active seismic sources.

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.

The author discusses the study "Lidar reveals uniform Alpine fault offsets and bimodal plate boundary rupture behavior, New Zealand," by Gregory P. De Pascale and colleagues, published online on March 17, 2014 by the journal "Geology." Topics addressed include dextral offsets at a creek near Gaunt Creek in New Zealand, the offsets' occurrence on a fault that is subsidiary to the Alpine fault, and the subsidiary fault's inability to produce single-event displacements.