Ice-marginal lakes are increasingly common around Greenland and are important for modulating glacier runoff and dynamics. This study investigates the evolution of a ~3 km2 and up to ~100 m deep ice-dammed lake at Isunnguata Sermia, West Greenland. Satellite observations between 1987 and 2024, and field observations of a 2023 drainage using passive seismics, GNSS and time-lapse imagery reveal that the lake drains subglacially and has undergone 12 fill-drain cycles since 1987, a drainage periodicity of 1-3 years. Peak lake volume has decreased since 2010, associated with glacier thinning. Lake drainage can perturb the wider subglacial hydrology system, including triggering the release of stored subglacial water along the flood path in 2019. During the extreme melt year of 2012, the lake drained but did not refill, suggesting that subglacial leakage under the ice dam was sustained by record runoff. Transient ice flow acceleration was observed during the late season drainage in 2023 when the subglacial hydrological system was less efficient and therefore more easily overwhelmed. Our results indicate that ice-dammed lake fill-drain cycles, and the downstream impact on subglacial hydrology and ice dynamics, are modulated by ice dam thickness, melt supply and the antecedent subglacial hydraulic capacity.

The design of ground-source heat pump systems depends on reliable determination of heat transport parameters, especially the ground thermal conductivity. An effective thermal conductivity, lambda eff, is traditionally calculated from in-situ thermal response testing (TRT), expressed as a bulk value for the depth range being tested. However, this practice is insensitive to heterogeneous heat transport within the ground, and flowing groundwater may significantly increase lambda eff. To characterise high- and/or heterogeneous-flow regimes, e.g. in fractured aquifers, distributed TRT observations are advantageous. Distributed TRTs using fibre-optic distributed temperature sensing (FO-DTS) have therefore been applied at a chalk site (Berkshire, southern UK) to assess heat flow and the depth variability of effective thermal conductivity and flow conditions, within boreholes reaching up to 100 m depth. With a vertical resolution of 0.5 m, FO-DTS can isolate different thermo-hydrogeological conditions in the chalk and particularly the groundwater flow horizons. Values of lambda eff, measured during a 3-day TRT, vary with depth between 5 and 30 W/m K, compared to thermal conductivities of 2.3-2.9 W/m K measured on chalk core samples. Zones of enhanced lambda eff correlate with highly permeable flow zones in the aquifer. However, when evaluated during a 7-day cooling phase, lambda eff is reduced by between 10-60% compared to values measured during heating, highlighting the potential influence of complex convection effects and vertical flow within the open borehole. Overall, this study illustrates the value of distributed spatial assessments of thermo-hydrogeological conditions, and the necessity of combining different testing approaches to characterise heat flow in dualporosity aquifers.

Soil structure degradation, particularly due to compaction and unstable watering regimes, poses significant challenges to sustainable agriculture. This problem is often exacerbated by inefficient irrigation management, irregular rainfall distribution, tillage processes and the cumulative effects of regular field traffic from agricultural machinery. These variables cumulatively diminish the soil’s structural stability, decreasing its ability to support plant development and increasing vulnerability to erosion and productivity loss. This study aims to understand how agricultural soils respond to wetting-drying cycles under various watering regimes, with a particular emphasis on changes in soil compaction. Furthermore, it assesses the ability of seismic surveys to continually and accurately detect volumetric changes and compaction dynamics caused by these regimes. To achieve this, seismic surveys, potentially expanded to fibre-optic distributed acoustic sensing, offer significant potential for high-resolution monitoring of subsurface soil dynamics, including indicators of soil compaction and soil densification. This method may offer new opportunities and a scalable approach for real-time monitoring of soil structure and compaction changes. To improve the reliability of survey data interpretation, additional validation will be conducted through in-situ measurements at the research site and geotechnical laboratory analyses. The results of this study are expected to provide new insights into the use of seismic survey techniques for real-time monitoring of soil compaction in precision agriculture. By enabling early detection and management of compaction-related issues, these findings can support the development of more effective and sustainable soil management strategies.

Abstract The evolution and connectivity of subglacial drainage systems control basal sliding and therefore modulate ice motion, yet direct observations of these systems remain limited. Here, we investigate hydraulic connectivity and its influence on ice motion at Isunnguata Sermia, a large land‐terminating outlet glacier of the Greenland Ice Sheet. We use “Cryoegg” wireless sensors to obtain moulin water pressure and electrical conductivity, in conjunction with passive seismics to measure glacio‐hydraulic tremor and GNSS‐derived measurements of ice motion. We identify rapid switching (<24 hr) of subglacial hydraulic connectivity between distinct subsystems: a large, primary drainage axis located in a deep trough, and secondary subglacial channels. When surface melt inputs are high, the secondary subsystem fed by the instrumented moulins connects with the efficient primary drainage axis and exhibits smoothed diurnal variability and synchronization with regional ice motion and seismic tremor. When surface melt decreases, hydraulic connectivity is reduced, and the secondary subsystem becomes disconnected and responds sensitively to variations in local melt inputs, increasing local meltwater residence time. Regional ice motion is controlled by the characteristics of the primary drainage axis and is insensitive to local inputs into the secondary subsystem.

A hydrologically-active subglacial lake system has been identified near the south lateral margin of Isunnguata Sermia, West Greenland. Differencing time-stamped ArcticDEM strips has revealed multiple anomalies in ice-surface elevation change. A large hydrological drainage event from Isunnguata Sermia in 2015 slowed ice flow for ~1 month and flooded the foreland, depositing up to 8 meters of sediment. Although the proglacial flooding provided evidence that the ice-surface elevation anomalies were likely caused by subglacial water bodies, satellite altimetry cannot provide direct insights into their thickness, structure and properties. Therefore, field-based geophysical measurements, including ground-based radar and active source seismics, were collected during summer 2023 and autumn 2024 to characterise the subglacial hydrological system. Radar data were collected in October 2024 using a 10 MHz Blue Systems Integration ice-penetrating radar (IPR) to determine ice thickness and constrain a subglacial hydrological model. 26 km of radar data were collected over two of the ice-surface elevation anomalies. The radar data cross existing airborne IPR transects and point measurements from a phase-sensitive radar (pRES). Active source seismic surveys were performed at three locations over the largest ice-surface elevation anomaly: 1) anomaly centre, 2) anomaly southern edge, and 3) between the anomaly centre and southern edge, where bright basal reflections had been identified from radar observations. Seismic data were acquired with a hammer and plate source and 48 100 Hz vertical component geophones in a 94 m-long spread at a geophone spacing of 2 m. Our radar results show that the ice-surface elevation anomalies overlie complex subglacial topography on the southern sidewall of the large over-deepened trough beneath the Isunnguata Sermia trunk. Across the largest surface anomaly, ice thickness varies between 380 m to 600 m. The seismic data shows a negative polarity at the ice-bed interface, coincident with a subglacial topographic low. This indicates an acoustically soft basal material, which could represent water or water-saturated sediment. Scattering and diffraction hyperbola in the radar data arise from a complex englacial structure, which have implications for attenuation of radio and sound energy. These observations provide new insights into the glaciology and hydrology of an important West Greenlandic outlet glacier and highlight the complexities associated with active glacier hydrological systems and their geophysical characterisation.

Basal conditions that facilitate fast ice flow are still poorly understood and their parameterization in ice‐flow models results in high uncertainties in ice‐flow and consequent sea‐level rise projections. Direct observations of basal conditions beneath modern ice streams are limited due to the inaccessibility of the bed. One approach to understanding basal conditions is through investigating the basal landscape of ice streams and glaciers, which has been shaped by ice flow over the underlying substrate. Bedform variation together with observations of ice‐flow properties can reveal glaciological and geological conditions present during bedform formation. Here we map the subglacial landscape and identify basal conditions of Rutford Ice Stream (West Antarctica) using different visualization techniques on novel high‐resolution 3D radar data. This novel approach highlights small‐scale features and details of bedforms that would otherwise be invisible in conventional radar grids. Our data reveal bedforms of <300 m in length, surrounded by bedforms of >10 km in length. We correlate variations in bedform dimensions and spacing to different glaciological and geological factors. We find no significant correlation between local (<3 × 3 km) variations in bedform dimensions and variations in ice‐flow speed and (surface or basal) topography. We present a new model of subglacial sediment discharge, which proposes that variations in bedform dimensions are primarily driven by spatial variation in sediment properties and effective pressure. This work highlights the small‐scale spatial variability of basal conditions and its implications for basal slip. This is critical for more reliable parameterization of basal friction of ice streams in numerical models.

The icy parts of the Earth, known as the cryosphere, are an integral part of the climate system. Comprehensively understanding the cryosphere, requires dense observations, not only of its surface, but also of its internal structure and dynamics. Seismic methods play a central role in this endeavour. Fibre-optic sensing is emerging as valuable complement and alternative to well-established electro-mechanical seismometers. Offering metre-scale channel spacing, interrogation distances of up to around 100 km, and a bandwidth from mHz to kHz, it has enabled new seismological applications, for instance, under water, in cities and on volcanoes. Cryosphere research particularly benefits from fibre-optic sensing because long cables can be deployed with relative ease in icy environments where dense arrays of seismometers are difficult to install, including glaciers, ice sheets and deep boreholes. Intended to facilitate future fibre-optic seismology research in the cryosphere, this Expository Review combines a classical publication review with theoretical background, a practical field guide, a cryospheric signal gallery, and open-access data examples for hands-on training. Following a summary of recent findings about firn and ice structure, glacial seismicity, hydrology and avalanche dynamics, we derive the ideal instrument response of a distributed fibre-optic deformation sensor. To approach this ideal in field experiments, we propose numerous practical dos and don'ts concerning the choice and handling of fibre-optic cables, required equipment, splicing in the field at low temperatures, cable layout and trenching, and the deployment and coupling of cables in boreholes. A cryospheric signal gallery provides examples of data from a wide range of sources, such as explosions, land and air traffic, electricity generators, basal stick-slip icequakes, surface crevassing, englacial icequake cascades, floating ice shelf resonance, surface water flow and snow avalanches. Many of these data are enclosed as an open-access training resource, together with code for reading, visualisation and simple analyses. This review concludes with a discussion of grand open challenges in our understanding of cryosphere structure and dynamics, and how further advances in fibre-optic sensing may help to overcome them.

The stability of Thwaites Glacier, the second largest marine ice stream in West Antarctica, is a major source of uncertainty in future predictions of global sea level rise. Critical to understanding the stability of Thwaites Glacier, is understanding the dynamics of the shear margins, which provide important lateral resistance that counters basal weakening associated with ice flow acceleration and forcing at the grounding line. The eastern shear margin of Thwaites Glacier is of interest as it is poorly topographically constrained, meaning it could migrate rapidly, causing further ice flow acceleration and drawing a larger volume of ice into the fast-flowing ice stream. In this study, we present an analysis of ~4000 icequakes, recorded over a two-year-period on a broadband seismic array deployed across the eastern shear margin of Thwaites Glacier. The array consisted of seven three-component seismometers, deployed around a central station in a circle, roughly 10 km in diameter. We use an automated approach to detect and locate “high-frequency” seismic events (10-90 Hz), the majority of which are concentrated in clusters around the ice-bed interface on the slow-moving side of the shear margin, as opposed to within the ice-stream itself. The event waveforms exhibit clear shear-wave splitting, indicative of the presence of an anisotropic ice fabric, likely formed within the shear margin, which is consistent with published radar studies from the field site. Initial analysis of the split shear-waves suggests that they can be used to better constrain the region's ice fabric, and likely used to infer past shear margin location and assess the future stability of this ice rheology.

Reconstructing past ice sheets is important for understanding the response of modern ice sheets to changes in climate. The evolution of the Weddell Sea Sector’s grounding line since the last glacial maximum (LGM) to its present position remains ambiguous; previous authors have proposed hypotheses both of monotonic grounding line retreat and of rapid grounding line retreat followed by readvance. However, distinguishing these scenarios with current observations remains difficult. To explore these scenarios, we report seismic measurements of basal properties at KIR, an ice rise in the Weddell Sea Sector, West Antarctica. A three-component seismic survey enabled detection of the compressional (P) wave reflection and the converted (PS) wave reflection (an incident P wave converted to a shear wave at the base-ice reflector) from the base of KIR. Amplitude-vs-angle (AVA) analysis aims to constrain the physical properties (namely density, seismic velocity, by measuring the variation of reflectivity with incidence angle at the reflector. By jointly inverting the AVA responses of the PP wave reflection and the PS reflection, we increase the confidence in the interpretation of the base-ice properties. Analysis of PP and PS AVA responses at KIR indicates that the reflection arises from a material with a P wave velocity of 4.03 ± 0.05 km/s, an S wave velocity of 2.16 ± 0.06 km/s and a density of 1.44 ± 0.06 g/cm3; these properties are consistent with a reflection from a layer of entrained basal debris, with 20-30% debris by volume. The observed properties are not indicative of interference at a thin layer, as observed beneath glaciers elsewhere. The absence of deeper subglacial reflections indicates a poorly-defined boundary between this basal debris layer and the underlying subglacial material, which we therefore propose consists of frozen sediments . If this interpretation is correct, the presence of a debris layer overlying basal frozen sediment indicates a potential retreat/readvance scenario for KIR. A possible scenario is a previous episode of flow during which KIR may have been weakly grounded as an ice rumple, followed by grounding on the lee side of the bathymetric high and subsequent freezing of subglacial sediments. However, the origin of such a homogeneous and debris-rich layer remains unclear. The indication of a reflection from a basal debris layer raises questions about whether conventionally interpreted basal reflections can truly be considered as such, and whether these interpretations may mask the true nature of the underlying subglacial material. This ambiguity may be most effectively reconciled by borehole sampling.

Hydrologically active subglacial lakes modulate subglacial hydrology, ice motion, microbial habitats, biogeochemical fluxes, and subglacial and proglacial geomorphic activity. The recent potential identification of active subglacial lakes beneath the ablation area of the Greenland Ice Sheet from repeat satellite altimetry data suggests that they are a significant yet poorly constrained component of the ice sheet hydrological system. These subglacial lakes, which are presumably fed by both supraglacial and subglacial water inputs, appear to be highly dynamic features that fill gradually (i.e. over years) but drain rapidly (i.e. hours to days), causing high discharge flood events observed in the proglacial area. While remote sensing observations constrain lake dynamics to a coarse temporal and spatial resolution the precise timing of lake filling and drainage and the detailed effect on ice dynamics can only be determined from field-based measurements. Here we present initial results from a comprehensive geophysical investigation of subglacial lake dynamics beginning in April 2023. We report measurements of horizontal and vertical ice surface motion together with horizontal strain rates from an array of 11 GNSS receivers installed across three juxtaposed subglacial lakes on Isunnguata Sermia — an ~6 km wide land-terminating outlet glacier in West Greenland. We combine these GNSS data with autonomous phase-sensitive radio echo sounding measurements of ice thickness and vertical strain to construct a time series of lake filling and drainage spanning the 2023 melt season. To investigate inter-relationships between subglacial lake hydrology and ice dynamics at both short (hourly) and seasonal timescales, we supplement these time series with data from an array of seismometers installed in between two of the lakes and at the glacier terminus, together with several kilometres of radio echo sounding measurements of ice thickness.

Urban geothermal solutions to heating and cooling have developed slowly in the UK, partly due to limited understanding of subsurface heat flow regimes and how stored heat might be sustainably governed within heterogeneous aquifers. Understanding heat flow through various aquifers is the goal of the SmartRes project, in which heat flow trials will be conducted in a number of sites. To provide context for heat flow experiments in a fractured chalk aquifer, geophysical surveys were acquired at Trumplett’s Farm, a groundwater abstraction and monitoring site near Reading (Berkshire, UK). Here, groundwater flow is primarily within a fracture network, likely in an active zone within the upper 10 m of the saturated chalk. Seismic surveys recorded energy generated with an impact source at surface geophones (24 cabled GEODE, and 20 nodal Smart-Solo, geophones) and hydrophone strings, deployed to 100 m depth in boreholes drilled at the site. Smart-Solo nodes were deployed in a ~10 x 5 m grid at the site, with cabled geophones occupying lines between adjacent boreholes, with geophone intervals of up to 2 m. Nodal geophones recorded passively throughout the 3-day deployment and will be analysed using ambient noise correlation to evaluate anisotropy. The remaining data has been used for preliminary analysis with MASW (Multichannel Analysis of Surface Waves), P-wave refraction velocities, and vertical seismic profiles (VSPs). MASW analyses suggest shear wave velocity (Vs) ranges from 250-600 m/s in the uppermost 1.5 m, but estimates are challenging given poor dispersion imaging of the fundamental mode. Different source-receiver offsets were tested to eliminate mode superposition, but the best dispersion curves are observed for zero-offset shots. Data were processed in a commercially available software with relatively limited freedom to adjust inversion parameters, hence further analysis will use the MuLTI code to undertake a constrained Monte Carlo inversion approach. The deeper structure of the chalk was characterised in VSPs, indicating reflective P-wave horizons at 52 and 69 m depth, separating material with interval velocities of ~2100 m/s, ~2500 m/s and 3000 m/s. Observing these reflections required aggressive frequency-wavenumber filtering to suppress direct waves in the water column. Electrical resistivity tomography (ERT) surveys were conducted using the BGS PRIME ERT system to optimise array configuration for long-term monitoring. The reconnaissance survey included in-hole, borehole-to-surface, and surface ERT at 1 m intervals, employing C1P1-C2P2 bipole-bipole and dipole-dipole arrays around the site. Preliminary ERT inversion revealed low resistivity zones within the top 1.5 – 2 m across the site and mapped a potential south-dipping high resistivity structure. A longer ERT survey spread is planned to better reveal hydrodynamic interactions at deeper depths. This initial insight will be refined with a fibre-optic distributed acoustic sensing deployment at the Trumplett’s site and an optimised repeat of the BGS PRIME ERT array. These will be synchronous with a thermal response test at the Trumplett’s site monitored with distributed temperature sensing. Keywords: Seismic analysis, ERT, geothermal investigation, fractured aquifer, aquifer thermal energy storage

This study presents high resolution mapping of moulins located above three subglacial lakes at Isunguata Sermia. Moulins are the primary pathway for transferring supraglacial melt to englacial and subglacial environments. The formation of moulins has been explained by the flow of water into a notch, associated with glacier structures and incision of supraglacial streams, which are directly related to glacier morphology and dynamics. Meltwater input to subglacial systems, along with glacier dynamics, will in turn affect the development of subglacial meltwater networks, which control glacier morphology and dynamics. This study focusses on Isunguata Sermia, West Greenland, which has an active subglacial drainage system that includes distinct subglacial lakes. Hydrologically connected or active subglacial lakes may be directly influenced by water input from supraglacial to englacial systems via moulins during the ablation season. Moulins were mapped using a combination of high resolution orthomosaics and digital elevation models derived from uncrewed aerial vehicle flights. Moulin locations and morphologies were compared with glacier structures, ice flow velocities, and bed topography. We reveal a distinct pattern of moulin locations relative to each subglacial lake and the locations of primary and secondary glacier structures an supraglacial hydrology. Furthermore, we also outline a clear morphological pattern, wherein morphology of moulins varies distinctly at with the location of each subglacial lake between vertical shafts, crevasse associated and keyhole morphology. These observations will be used to consider the efficiency of meltwater routing from the surface to the bed, and the potential for inputs to subglacial lakes, and the wider implications for varying ice flow velocity and evolution of the subglacial drainage system.

Deep-seated bedrock landslides contribute to rapid landscape evolution, often resulting in transient erosion rates that exceed long-term average rates of tectonic uplift. Understanding the spatiotemporal patterns of such landslides reveals past drivers of landscape evolution and helps predict how the landscape will respond in the future. The Nooksack River watershed (NRW), Whatcom County, Washington, USA, features numerous paleo landslides linked to high relief, seismic activity, local geologic structures, and abundant precipitation. Specifically, Holocene surface rupturing earthquakes on the Boulder Creek Fault (BCF) are a likely triggering mechanism for widespread prehistoric landsliding. To determine the relative importance of several probable drivers of past bedrock landsliding, we investigate spatiotemporal trends of 440 landslides using a calibrated relationship between lidar-based deposit surface roughness and radiocarbon-based age. We find the roughness-age relationship in Washington's Cascade Range is consistent with that of bedrock landslides in Oregon's coast range. Our observed landslide frequency history best matches a modeled history that incorporates preservation bias and two coseismic landslide pulses, each comprising 6.5 % of the total landslides, at known times of surface rupturing earthquakes on the BCF in the last 4,000 years. Both the density of past bedrock landslides and size of plausible coseismic landslides peak near the Holocene scarps of the BCF and decrease with distance from the fault. These findings suggest surface rupturing earthquakes on the BCF measurably affected spatiotemporal landslide patterns and watershed evolution in the NRW, highlighting the importance of considering coseismic landslides in regional hazard assessment and planning.

The rate of ice loss from marine terminating glaciers is governed by both surface runoff and ice dynamics. Although ice loss due to runoff can be relatively easily studied using in-situ and remote sensing methods, ice dynamics are more difficult to constrain and are the largest contributor to uncertainty in ice loss estimates. By recording and locating the source of seismic signals released during (e.g.) crevasse opening and stick-slip events, we can obtain a spatial and temporal distribution of icequakes. This will allow for estimates of stress and strain within Sermeq Kujalleq (Store Glacier), West Greenland. The emerging technology of distributed acoustic sensing (DAS) offers the ability to perform seismic surveys at higher spatial sampling resolutions than is feasible with conventional geophone deployments. This is especially true when instruments are required to be deployed in a logistically challenging environment such as Store Glacier. Here, we present an icequake source location method that exploits the dense spatial sampling of DAS alongside the directionality and increased signal to noise ratio of 3-component geophones. Both instruments were deployed in closely drilled boreholes on Store Glacier in July 2019, as part of the RESPONDER project. The DAS fiber optic cable was deployed in a 1043 m deep borehole. The three geophones are at depths of 100 m, 250 m and 400 m. The data set includes controlled-source vertical seismic profiles (VSPs) and a 3-day passive record of cryoseismicity recorded by both instrument types. Previous work on the passive DAS dataset created a convolutional neural network-based method that performs efficient signal detection in the frequency-wavenumber domain and provided a catalogue of detections at a mean rate of 4074 per hour. The next step is to locate the catalogued seismic sources in targeted time periods containing arrivals. Our borehole DAS deployment only records the vertical component of a seismic signal because of the fiber optic cable’s sensitivity only to strain along its longitudinal axis. This renders it impossible to determine the backazimuth of arrivals solely using the DAS data. To overcome this limitation, we analyse the particle motion recorded by the 3-component geophones. The 3D source location can be derived using well-resolved estimates of source depth and distance from the DAS data, plus the backazimuth gained from geophones. Our initial results include an estimated location of the source of one large icequake at ~800 m offset from the borehole and ~300 m depth. The backazimuth of these arrivals is yet to be determined, but the depth of this event suggests it may originate from an englacial shear zone related to a temperature anomaly that we have inferred in Store Glacier from distributed temperature sensing. Once efficiently automated, we aim to combine the seismic observations to build a catalogue of seismicity, including event time and origin location. Additional work aims to estimate moment tensors of these detected and located events to improve our understanding of Store Glacier’s dynamics.

The accuracy of sea-level rise predictions is highly dependent on reliably understanding the subglacial environment beneath ice streams. Bedforms result from the interaction between ice and its substrate, and therefore have the potential to shed light on poorly understood basal conditions influencing ice dynamics. However, theoretical models of bedform formation are often based on observations from deglaciated areas or from sparsely-sampled geophysical surveys over glaciated regions. Here, we use high-resolution three- and two-dimensional radar and seismic data to reveal details of the initiation and evolution of a subglacial bedform beneath Rutford Ice Stream, West Antarctica. Radar surveys at 20 m and 50 m line spacing allow detailed imaging of bed topography, including a moat up to 55 m deep, surrounding the upstream end of a 50-m high and >18-km long bedform. Many models rely on either a topographical or a locally resistant seed point to initiate bedform formation. The bedform described here is mostly composed of soft sediment (porosity >0.3) and lacks a boulder or outcrop, suggesting the bedform initiated without a topographic seed point. Sediment at the upstream end of bedforms appears stiffer over a distance of 2.3 km. We suggest sediment inhomogeneities in the initially flat bed cause the deposition of sediment, which, assuming resistant enough, acts as a seed point for bedform extension and moat erosion. The moat's geometry and its truncation of other bedforms suggest that it was eroded after the deposition of surrounding bedforms. These observations from a modern ice stream deliver information of subglacial processes involved in the initiation as well as in situ high-resolution topography and properties of bedforms and moats. Using these observations numerical models can be tested and developed accordingly.

ABSTRACT Earthquake-induced landslides can record information about the seismic shaking that generated them. In this study, we present new mapping, Light Detection and Ranging-derived roughness dating, and analysis of over 1000 deep-seated landslides from the Puget Lowlands of Washington, U.S.A., to probe the landscape for past Seattle fault earthquake information. With this new landslide inventory, we observe spatial and temporal evidence of landsliding related to the last major earthquake on the Seattle fault ∼1100 yr before present. We find spatial clusters of landslides that correlate with ground motions from recent 3D kinematic models of Seattle fault earthquakes. We also find temporal patterns in the landslide inventory that suggest earthquake-driven increases in landsliding. We compare the spatial and temporal landslide data with scenario-based ground motion models and find stronger evidence of the last major Seattle fault earthquake from this combined analysis than from spatial or temporal patterns alone. We also compare the landslide inventory with ground motions from different Seattle fault earthquake scenarios to determine the ground motion distributions that are most consistent with the landslide record. We find that earthquake scenarios that best match the clustering of ∼1100-year-old landslides produce the strongest shaking within a band that stretches from west to east across central Seattle as well as along the bluffs bordering the broader Puget Sound. Finally, we identify other landslide clusters (at 4.6–4.2 ka, 4.0–3.8 ka, 2.8–2.6 ka, and 2.2–2.0 ka) in the inventory which let us infer potential ground motions that may correspond to older Seattle fault earthquakes. Our method, which combines hindcasting of the surface response to the last major Seattle fault earthquake, using a roughness-aged landslide inventory with forecasts of modeled ground shaking from 3D seismic scenarios, showcases a powerful new approach to gleaning paleoseismic information from landscapes.

Masonry arch bridges continue to form a pivotal part of the transport networks of the UK and many other countries worldwide. However, their three-dimensional response (3D) under loading has to date been relatively little investigated. Here, details of a large-scale masonry arch bridge load tested to failure under laboratory conditions are presented. The bridge consisted of a brickwork arch barrel, abutments, spandrel walls, and compacted limestone as backfill material. Patch loading was applied to the surface of the backfill at the quarter and three-quarter span points to assess the failure mechanism, load-carrying capacity, and residual strength of the bridge. A range of sensors were employed to capture the 3D bridge response and ground-penetrating radar surveys were performed on both the virgin and load-tested bridge to compare its internal structure. The observed evolution of cracks and post-test deformed geometry demonstrated the presence of both a localised 3D mode of response in the arch barrel in the vicinity of the applied load and a global four-hinge mechanism. Failure-level load tests carried out first at the quarter span and then at the three-quarter span points showed that the load-carrying capacity of the bridge had reduced by only 10 % in the second test, though the stiffness of the bridge had decreased by around 35 %. During the failure-level load tests, significant in-plane and out-of-plane deformations of the spandrel walls were also observed, adding to the much smaller residual deformations recorded in low- and mid-level load tests.