Seabed fluid seepage is a dynamic process that modulates gas and heat transfer between the Earth’s interior and the ocean. In submarine volcanic settings, short-term changes in hydrothermal seep behaviour can provide tangible indicators of volcanic activity. However, such signals are rarely, if ever, observed directly. Here, we show that passive acoustic monitoring can resolve tidally controlled variability in condensable bubble dynamics at the Calypso hydrothermal vent field in the Bay of Plenty, New Zealand. Over three days of acoustic recording, we detect an exceptionally large number of acoustic emissions. We demonstrate they are vapour-rich bubble sounds generated by boiling fluids within unconsolidated sediments. Systematic changes in sound frequency of bubbles condensing in sub-cooled water reveal cyclic transitions in fluid phase. Therefore, tidal loading may constrain high-temperature fluid expulsion, directly modulating seep intensity and heat flux. These results establish passive acoustics as a powerful high-resolution monitoring tool of transient sub-seabed processes in hydrothermal systems. This study provides a new window into the physics of condensable bubbles in extreme environmental conditions, with implications for volcanic hazard assessment.

The Kāpiti Marine Reserve (KMR) in New Zealand, established in 1992, aims to protect representative marine ecosystems and benthic habitats in the region. This study focuses on white-striped sea anemone (Anthothoe albocincta) and rhodolith (Sporolithon durum) beds as key habitat-forming taxa and compares the spatial representation of predicted suitable habitat under the current boundary and an initially proposed boundary configuration developed prior to stakeholder involvement. It integrates high-resolution acoustic mapping, sediment grain size models, and oceanographic data to produce substrate and habitat suitability models for both habitats and to assess habitat representation relative to reserve boundaries and adjacent seafloor outside KMR. Seafloor morphometric and texture features were derived from acoustic data, and extensive seasonal oceanographic summaries were incorporated to capture environmental variability. A Random Forest classifier was used for substrate mapping, and Maximum Entropy modelling for habitat suitability. The full feature set achieved the highest substrate classification performance (accuracy ≈ 0.736, F1 ≈ 0.732, Kappa ≈ 0.602). Habitat suitability models also showed strong predictive performance, with True Skill Statistic (TSS) ≈ 0.89 and Area Under the Curve (AUC) ≈ 0.97 for anemone beds, and TSS ≈ 0.93 and AUC ≈ 0.98 for rhodolith beds. Predicted high-suitability habitats for both taxa were predominantly located outside the KMR boundaries at both suitability thresholds (0.5 and 0.7). At the 0.5 threshold, the initially proposed boundary encompassed 42.3% of anemone and 16.1% of rhodolith habitat, compared to 8.9% and 12.7% under the current boundaries. At the 0.7 threshold, coverage was 34.8% and 19.0% under the proposed configuration, compared to 6.1% and 14.2% under the current boundaries. These results demonstrate that integrating acoustic and environmental predictors improves habitat suitability modelling and provides a robust framework for assessing the spatial representation of predicted benthic habitat in relation to marine reserve boundaries.

Documenting and characterizing past submarine landslides is fundamental to understanding their distribution and frequency through time, and critical to assessing the associated hazard. The widespread availability of marine geophysical data at the active Hikurangi subduction margin, east of Aotearoa New Zealand, provides an excellent basis to map regional trends in landslide occurrence. We present a database that documents mass transport deposits (MTDs) in 30 marine geophysical surveys, encompassing ∼45,400 line‐km of 2D seismic profiles. We map and characterize 737 MTDs, showing variations in size, location and style of failure, which we attribute to changes in geomorphic setting from north to south. Mass transport deposits in the northern Hikurangi margin, characterized by a high taper wedge and seamount subduction, show a broad range in size, with the highest proportion of MTDs displaying blocky or intact internal architecture. The central margin, characterized by lower wedge taper, hosts the most MTDs (51%), albeit with the thinnest (on average) and clustering within interridge basins. The southern Hikurangi margin hosts widespread submarine canyons and the largest (on average) MTDs, based on area and thickness. We demonstrate the importance of seismic archives in providing new insights into MTD preservation and discuss the bias between seafloor geomorphology and subseafloor seismic data in quantifying MTD occurrence. Our findings support the interrogation of the varied and complex causes of submarine landslides along active margins generally, as well as regions prone to cascading geohazards and landslide‐induced tsunami.

Submarine landslides can generate destructive tsunamis. Yet their recurrence intervals and tsunamigenic mechanisms are poorly understood, hampering quantification of global exposure and risk. With growing coastal populations and climatic changes, the impacts of tsunami hazards will increase, and will disproportionately affect peoples in underdeveloped countries (e.g., Small Island Developing States). Specific hazard characteristics of submarine landslide-tsunami include the potential for: short tsunami travel times, highly directional waves, locally extreme wave amplitudes and lack of forewarning. Probabilistic tsunami hazard assessments (PTHA) have emerged as the gold standard for tsunami hazard quantification, enabling science understanding to be translated into policy and decision making. However, our knowledge gaps and research challenges largely prohibit PTHA for submarine landslide sources. In this review, we reference Aotearoa New Zealand, as a western Pacific Island nation vulnerable to tsunami hazards, to illustrate the fragmentary nature of the evidence for, and perceived threat of submarine landslide-tsunami typical of many regions globally. We present an overview of geoscience approaches for the identification and assessment of submarine landslide-tsunami hazards, which include construction of submarine landslide databases, source-specific numerical tsunami simulations, successful approaches to submarine landslide-specific PTHA, submarine landslide susceptibility mapping and emerging data science techniques. We recommend a sequence of logical and accessible steps for enhanced submarine landslide identification and hazard assessment aimed at geoscience disciplines. Our recommendations promote strategic approaches to future data collection and enhanced multi-disciplinary collaboration between marine geoscientists, and tsunami, hydrodynamic, hazard and risk specialists.

Detecting and characterizing oceanic seep sites is of considerable interest for the geoscience community due to their influence on global climate, ecological significance, connection to resources of high value, and, in many locations including New Zealand, their cultural importance. Modern acoustic systems provide the means for quantitative analysis of seep systems by collection of backscattered energy by gas bubbles and associated water column phenomena and surrounding seafloor. The July 2018 international, multi-institution Quantitative Ocean-Column Imaging (QUOI) voyage aimed to develop protocols and methodologies for identifying and quantifying seafloor and water-column backscatter data associated with bubble seep sites utilizing a large range of active acoustic systems and direct sampling methods. Here, we will provide an overview of QUOI voyage goals and research activities at several locations offshore of New Zealand, including the Calypso hydrothermal vent field in the Bay of Plenty. Gas bubble and hydrothermal fluid emission were captured in acoustic water column data, video transects, and direct sampling operations. More than 3000 individual seep bases were identified in the Calypso hydrothermal vent field, occupying approximately 9 of 115 km2 of mapped seafloor. Efforts are underway to characterize the bubble size distribution of seep sites and quantify carbon flux to the atmosphere using a combination of broadband acoustic methods and in-situ measurements.

Over the past few years, improvements in broadband split-beam echosounders have made it possible to obtain precise measurements of bubble-size distribution and density of gas seeps. Here, we model acoustic volume backscattering of a group of bubbles with a multi-modal size distribution that we matched to real-time acoustical measurement over a gas seep. The results are profiles of bubble size distribution descriptors (e.g., distribution type and parameters), density and ratio of the various components (i.e., gas composition). To test the ability of this methodology to differentiate gas flux composition and estimate gas flux magnitudes, we applied it in a semi-automated fashion on broadband data (12 to 250 kHz) acquired in the Bay of Plenty (NZ) over mixed gas seeps (e.g., CO2, CH4). Model outputs were compared with real-time dissolved gas measurements to constrain gas composition, magnitude, and ground-truth methodologies. The method can be applied to a variety of marine seeps to produce regional flux estimations, improving oceanic carbon budgets and our understanding of downstream feedbacks, such as localized deoxygenation or ocean acidification.

Understanding fluid expulsion is key to estimating gas exchange volumes between the seafloor, ocean, and atmosphere; for locating key ecosystems; and geohazard modelling. Locating active seafloor fluid expulsion typically requires acoustic backscatter data. Areas of very-high seafloor backscatter, or “hardgrounds,” are often used as first-pass indicators of potential fluid expulsion. However, varying and inconsistent spatial relationships between active fluid expulsion and hardgrounds means a direct link remains unclear. Here, we investigate the links between water-column acoustic flares to seafloor backscatter and bathymetric metrics generated from two calibrated multibeam echosounders. Our site, the Calypso hydrothermal vent field (HVF) in the Bay of Plenty, Aotearoa/New Zealand, has an extensive catalogue of vents and seeps in <250 m water depth. We demonstrate a method to quantitatively link active fluid expulsion (flares) with seafloor characteristics. This allows us to develop predictive spatial models of active fluid expulsion. We explore whether data from a low (30 kHz), high (200 kHz), or combined frequency model increases predictive accuracy of expulsion locations. This research investigates the role of hardgrounds or surrounding sediment cover on the accuracy of predictive models. Our models link active fluid expulsion to specific seafloor characteristics. A combined model using both the 30 and 200 kHz mosaics produced the best results (predictive accuracy: 0.75; Kappa: 0.65). This model performed better than the same model using individual frequency mosaics as input. Model results reveal active fluid expulsion is not typically associated with the extensive, embedded hardgrounds of the Calypso HVF, with minimal fluid expulsion. Unconsolidated sediment around the perimeter of and between hardgrounds were more active fluid expulsion sites. Fluids exploit permeable pathways up to the seafloor, modifying and refashioning the seafloor. Once a conduit self-seals, fluid will migrate to a more permeable pathway, thus reducing a one-to-one link between activity and hardgrounds. Being able to remotely predict active and inactive regions of fluid expulsion will prove a useful tool in rapidly identifying seeps in legacy datasets, as well as textural metrics that will aid in locating nascent, senescent, or extinct seeps when a survey is underway.

With the COVID-19 pandemic came what media has deemed the “port congestion pandemic”. Intensified by the pandemic, the commonplace anchoring of high-tonnage ships causes a substantial geomorphologial footprint on the seabed outside marine ports globally, but isn’t yet quantified. We present the first characterisation of the footprint and extent of anchoring in a low congestion port in New Zealand-Aotearoa, demonstrating that high-tonnage ship anchors excavate the seabed by up to 80 cm, with the impacts preserved for at least 4 years. The calcuated volume of sediment displaced by one high-tonnage ship (> 9000 Gross Tonnage) on anchor can reach 2800 m3. Scaled-up globally, this provides the first estimates of the footprint of anchoring to the coastal seabed, worldwide. Seafloor damage due to anchoring has far-reaching implications for already stressed marine ecosystems and carbon cycling. As seaborne trade is projected to quadruple by 2050, the poorly constrained impacts of anchoring must be considered to avoid irreversible damage to marine habitats.

The shallow marine environment represents a region of high biological productivity, ecological diversity, and complex oceanographic conditions, and often supports various human activities and industries. Mapping of the seafloor in shallow marine environments reveals seafloor features in detail, shedding light on a range of natural and anthropogenic processes. We present a high-resolution (2-m) multibeam dataset, combined with geologic samples that reveals a complete map of the seafloor from the land-water interface to similar to 350 m water depth within Queen Charlotte Sound/Totaranui (QCS) and Tory ChanneVKura Te Au (TC), Marlborough Sounds, New Zealand. These data reveal that the seafloor geomorphology and distribution of natural and anthropogenic features varies spatially from the inner QCS to the Cook Strait. Tidal currents play a large role in the erosion, transport, and deposition of sediments in QCS and TC. The distribution and depth of seafloor scouring suggests that tidal flow is locally intensified by coastal geometry and bathymetric barriers, resulting in concentrated scouring where tidal flow is restricted or redirected. In addition, superimposed bedforms reflect localized variations in flow direction that have likely developed across a range of spatial and temporal scales. Evidence for extensive seafloor fluid expulsion is preserved in > 8500 pockmarks mainly located within the inner and central QCS. The size and spatial distribution of pockmarks suggest multiple fluid sources in the region. The cumulative anthropogenic footprint on the seafloor within QCS represents 6.4 km(2) (similar to 1.5%) of the total seafloor area and is predominantly related to maritime activities including anchor dragging (47.5%) and mooring blocks (24%). This study provides a unique example of the information that can be revealed by a comprehensive survey programme that mapped from the land-water interface to the subtidal zone. Results presented in this study form a robust basis upon which to develop improved hydrodynamic models and benthic habitat maps and to assess the full extent of anthropogenic activities in the shallow marine realm.

The distribution of benthic ecosystems, dominated by filter-feeding communities, is highly influenced by the seabed geomorphology. However, the spatial variation in settlement of these species is also affected by near-bottom currents and any changes in light, nutrient concentration and food quality often associated with increases of suspended sediment concentrations within the water column. Detailed predictions of the geographic distribution of filter-feeder species and a deeper understanding of the physical processes influencing their distribution patterns is key for effective management and conservation. To date, predictive distribution modelling has been derived essentially from geomorphological parameters, mainly using spatially limited observations. In this study, seabed mapping, oceanographic modelling, hydrographic records and biological observations are integrated to provide high-resolution prediction of filter-feeder habitat distribution within Queen Charlotte Sound/Tōtaranui and Tory Channel/Kura Te Au, South Island of New Zealand. The aim is to evaluate potential suitable habitat areas for filter-feeders to inform where habitat restoration management should focus efforts to recover communities such as the horse mussel (Atrina zelandica) or the green-lipped mussel (Perna canaliculus), both of which have high economic impact in New Zealand. To accomplish this, Maximum Entropy (MaxEnt) predictive modelling was used to produce Habitat Suitability (HS) maps, using geomorphological parameters and seafloor classification information. Final HS maps also incorporated oceanographic and sediment dynamic information, showing that filter-feeder habitat distribution is highly influenced by the hydrodynamics and sedimentary processes apart from the seafloor geomorphology. Filter-feeder communities inhabit quiescent areas, limited by depth, slope and sediment type; and coincide with regions presenting low near-bottom currents and low turbidity levels. Additionally, the obtained results reveal the effects of the coastal settlements and major marine traffic routes, limiting the suitable habitats to areas with less human impact. This study demonstrates that a multidisciplinary approach is crucial to better predict the spatial distribution of benthic communities, which is key to improve benthic habitat restoration and recovery assessments.

Identifying the geomorphology and biogenic habitats of an area are essential to understanding the processes influencing species' distributions, ecological interactions, and managing the marine environment. We mapped the seafloor around Kapiti Marine Reserve, New Zealand, using a 30 kHz multibeam echosounder, to produce highly detailed bathymetric and backscatter maps of the marine reserve and surrounding area. We used these data and morphometric derivatives to generate a 14-class Benthic Terrain Model (BTM). We combined the BTM with the backscatter facies to create 18 sampling zones; these were used to inform the spatial distribution of sampling for ground truthing and to define biogenic habitats. Ground truthing included 214 camera drops, 12 sled tows, and 46 dives. We present here the compilation of ground truthing and multibeam data to reveal the diversity of physical and biogenic habitats that comprise the submarine landscape surrounding Kapiti Island, which include soft sediments with associated infaunal communities, large areas of rock rubble and gravels with mobile invertebrates, extensive anemone and rhodolith beds, boulder fields with dense macroalgal stands, flat and complex rocky reefs encrusted with a diversity of macroinvertebrates and macroalgae. This multidisciplinary and scalar approach supports a greater ability to effectively manage the area and promote awareness of the richness, diversity, and complexity of the seafloor and the biota it supports of the Kapiti Island region.

Detailed knowledge of the shape of the seafloor is crucial to humankind. Bathymetry data is critical for safety of navigation and is used for many other applications. In an era of ongoing environmental degradation worldwide, bathymetry data (and the knowledge derived from it) play a pivotal role in using and managing the world's oceans in a way that is in accordance with the United Nations Sustainable Development Goal 14 - conserve and sustainably use the oceans, seas and marine resources for sustainable development. However, the vast majority of our oceans is still virtually unmapped, unobserved, and unexplored. Only a small fraction of the seafloor has been systematically mapped by direct measurement. The remaining bathymetry is predicted from satellite altimeter data, providing only an approximate estimation of the shape of the seafloor. Several global and regional initiatives are underway to change this situation. This paper presents a selection of these initiatives as best practice examples for bathymetry data collection, compilation and open data sharing as well as the Nippon Foundation-GEBCO (The General Bathymetric Chart of the Oceans) Seabed 2030 Project that complements and leverages these initiatives and promotes international collaboration and partnership. Several non-traditional data collection opportunities are looked at that are currently gaining momentum as well as new and innovative technologies that can increase the efficiency of collecting bathymetric data. Finally, recommendations are given toward a possible way forward into the future of seafloor mapping and toward achieving the goal of a truly global ocean bathymetry.

Hydrogeological processes influence the morphology, mechanical behavior, and evolution of subduction margins. Fluid supply, release, migration, and drainage control fluid pressure and collectively govern the stress state, which varies between accretionary and nonaccretionary systems. We compiled over a decade of published and unpublished acoustic data sets and seafloor observations to analyze the distribution of focused fluid expulsion along the Hikurangi margin, New Zealand. The spatial coverage and quality of our data are exceptional for subduction margins globally. We found that focused fluid seepage is widespread and varies south to north with changes in subduction setting, including: wedge morphology, convergence rate, seafloor roughness, and sediment thickness on the incoming Pacific plate. Overall, focused seepage manifests most commonly above the deforming backstop, is common on thrust ridges, and is largely absent from the frontal wedge despite ubiquitous hydrate occurrences. Focused seepage distribution may reflect spatial differences in shallow permeability architecture, while diffusive fluid flow and seepage at scales below detection limits are also likely. From the spatial coincidence of fluids with major thrust faults that disrupt gas hydrate stability, we surmise that focused seepage distribution may also reflect deeper drainage of the forearc, with implications for pore-pressure regime, fault mechanics, and critical wedge stability and morphology. Because a range of subduction styles is represented by 800 km of along-strike variability, our results may have implications for understanding subduction fluid flow and seepage globally.

An international research group recorded the acoustic signatures of gas bubbles rising from a hydrothermal vent field to gather clues about greenhouse gases escaping into the atmosphere.

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

Using automated supervised segmentation of multibeam backscatter data to delineate seafloor substrates is a relatively novel technique. Low-frequency multibeam echosounders (MBES), such as the 12-kHz EM120, present particular difficulties since the signal can penetrate several metres into the seafloor, depending on substrate type. We present a case study illustrating how a non-targeted dataset may be used to derive information from multibeam backscatter data regarding distribution of substrate types. The results allow us to assess limitations associated with low frequency MBES where sub-bottom layering is present, and test the accuracy of automated supervised segmentation performed using SonarScope® software. This is done through comparison of predicted and observed substrate from backscatter facies-derived classes and substrate data, reinforced using quantitative statistical analysis based on a confusion matrix. We use sediment samples, video transects and sub-bottom profiles acquired on the Chatham Rise, east of New Zealand. Inferences on the substrate types are made using the Generic Seafloor Acoustic Backscatter (GSAB) model, and the extents of the backscatter classes are delineated by automated supervised segmentation. Correlating substrate data to backscatter classes revealed that backscatter amplitude may correspond to lithologies up to 4 m below the seafloor. Our results emphasise several issues related to substrate characterisation using backscatter classification, primarily because the GSAB model does not only relate to grain size and roughness properties of substrate, but also accounts for other parameters that influence backscatter. Better understanding these limitations allows us to derive first-order interpretations of sediment properties from automated supervised segmentation.

Multibeam echosounders are becoming widespread for the purposes of seafloor bathymetry mapping, but the acquisition and the use of seafloor backscatter measurements, acquired simultaneously with the bathymetric data, are still insufficiently understood, controlled and standardized. This presents an obstacle to well-accepted, standardized analysis and application by end users. The Marine Geological and Biological Habitat Mapping group (Geohab.org) has long recognized the need for better coherence and common agreement on acquisition, processing and interpretation of seafloor backscatter data, and established the Backscatter Working Group (BSWG) in May 2013. This paper presents an overview of this initiative, the mandate, structure and program of the working group, and a synopsis of the BSWG Guidelines and Recommendations to date. The paper includes (1) an overview of the current status in sensors and techniques available in seafloor backscatter data from multibeam sonars; (2) the presentation of the BSWG structure and results; (3) recommendations to operators, end-users, sonar manufacturers, and software developers using sonar backscatter for seafloor-mapping applications, for best practice methods and approaches for data acquisition and processing; and (4) a discussion on the development needs for future systems and data processing. We propose for the first time a nomenclature of backscatter processing levels that affords a means to accurately and efficiently describe the data processing status, and to facilitate comparisons of final products from various origins.

During the 2016, Mw 7.8 Kaikōura earthquake the Kekerengu fault ruptured the ground surface producing a maximum of ~12 m of net displacement (dextral-slip with minor reverse- slip), one of the largest five co-seismic surface rupture displacements so far observed globally. This thesis presents the first combined onshore to offshore dataset of co-seismic ground-surface and vertical seabed displacements along a near-continuous ~83 km long strike-slip dominated earthquake surface rupture of large slip magnitude. Onshore on the Kekerengu, Jordan Thrust, Upper Kowhai, and Manakau faults, we measured the displacement of 117 cultural and natural markers in the field and using airborne LiDAR data. Offshore on the dextral-reverse Needles fault, multibeam bathymetric and high-resolution seismic reflection data image a throw of the seabed of up to 3.5±0.2 m. Mean net slip on the total ~83 km rupture was 5.5±1 m, this is an unusually large mean slip for the rupture length compared to global strike-slip surface ruptures. Surveyed linear features that extend across the entire surface rupture zone show that it varies in width from 13 to 122 m. These cultural features also reveal the across-strike distribution of lateral displacement, 80% of which is, on average, concentrated within the central 43% of the rupture zone. Combining the near-field measurements of fault offset with published, far-field InSAR, continuous GPS, and coastal deformation data, suggests partitioning of oblique plate convergence, with a significant portion of co-seismic contractional deformation (and uplift) being accommodated off-fault in the hanging-wall crust to the northwest of the main rupturing faults. This thesis also documents in detail the onshore extent of surface fault rupture on the Kekerengu, Jordan Thrust, Upper Kowhai and Manakau faults. I present large-scale maps (up to 1:3,000) and documentary field photographs of this 53 km-long onshore surface rupture zone utilizing field data, post-earthquake LiDAR-derived Digital Elevation Models (DEMs), and post-earthquake ortho-rectified aerial photography. Ground deformation data is most detailed near the Marlborough coast where the 2016 rupture trace is well-exposed on agricultural grassland on the Kekerengu fault. In the southwest, where surface fault rupture traversed the alpine slopes of the Seaward Kaikoura ranges, fault mapping relied heavily on the LiDAR-derived DEMs. At 24 sites along the Kekerengu fault, I document co-seismic wear striae that were formed during the earthquake and were preserved on free face fault exposures. Nearly all of these striae were distinctly curved along their length, demonstrating that the direction of near-surface fault slip changed with time during rupture of the Kekerengu fault. Co-seismic displacement on the Kekerengu fault initiated as oblique-dextral (mainly dextral-reverse), and subsequently rotated to become nearly-pure dextral slip. These slip trajectories agree with directions of net displacements derived from offset linear features at nearby sites. Temporal rotation of the slip direction may suggest a state of low shear stress on the Kekerengu fault before the earthquake, and a near-complete reduction in stress during the earthquake, as has been inferred for other historic earthquakes that show evidence for changing slip direction with time.