Dynamic modeling of sequences of earthquakes and aseismic slip (SEAS) provides a self-consistent, physics-based framework to connect, interpret, and predict diverse geophysical observations across spatial and temporal scales. Amid growing applications of SEAS models, numerical code verification is essential to ensure reliable simulation results but is often infeasible due to the lack of analytical solutions. Here, we develop two benchmarks for three-dimensional (3D) SEAS problems to compare and verify numerical codes based on boundary-element, finite-element, and finite-difference methods, in a community initiative. Our benchmarks consider a planar vertical strike-slip fault obeying a rate- and state-dependent friction law, in a 3D homogeneous, linear elastic whole-space or half-space, where spontaneous earthquakes and slow slip arise due to tectonic-like loading. We use a suite of quasi-dynamic simulations from 10 modeling groups to assess the agreement during all phases of multiple seismic cycles. We find excellent quantitative agreement among simulated outputs for sufficiently large model domains and small grid spacings. However, discrepancies in rupture fronts of the initial event are influenced by the free surface and various computational factors. The recurrence intervals and nucleation phase of later earthquakes are particularly sensitive to numerical resolution and domain-size-dependent loading. Despite such variability, key properties of individual earthquakes, including rupture style, duration, total slip, peak slip rate, and stress drop, are comparable among even marginally resolved simulations. Our benchmark efforts offer a community-based example to improve numerical simulations and reveal sensitivities of model observables, which are important for advancing SEAS models to better understand earthquake system dynamics.

Catastrophic failure of brittle rocks is important in managing risk associated with system-sized material failure. Such failure is caused by nucleation, growth and coalescence of micro-cracks that spontaneously self-organize along localized damage zones under compressive stress. Here we present x-ray micro-tomography observations that elucidate the in-situ micron-scale processes, obtained from novel tri-axial compression experiments conducted in a synchrotron. We examine the effect of microstructural heterogeneity in the starting material (Ailsa Craig micro-granite; known for being virtually crack-free) on crack network evolution and localization. To control for heterogeneity, we introduced a random nano-scale crack network into one sample by thermal stressing, leaving a second sample as-received. By assessing the time-dependent statistics of crack size and spatial distribution, we test the hypothesis that the degree of starting heterogeneity influences the order and predictability of the phase transition between intact and failed states. We show that this is indeed the case at the system scale. The initially more heterogeneous (heat-treated) sample showed clear evidence for a second-order transition: inverse power-law acceleration in correlation length with a well-defined singularity near failure, and distinct changes in the scaling exponents. The more homogeneous (untreated) sample showed evidence for a first-order transition: exponential increase in correlation length associated with distributed damage and unstable crack nucleation ahead of abrupt failure. In both cases, anisotropy in the initial porosity dictated the fault orientation, and system-sized failure occurred when the correlation length approached the grain size. These results have significant implications for the predictability of catastrophic failure in different materials.

Geodynamic codes have become fast and efficient enough to facilitate sensitivity analysis of rheological parameters. With sufficient data, they can even be inverted for. Yet, the geodynamic inverse problem is often regularized by assuming a constant geometry of the geological setting (e.g. shape, location and size of salt diapirs or magma bodies) or approximating irregular bodies with simple shapes like boxes, spheres or ellipsoids to reduce the parameter space. Here, we present a simple and intuitive method to parameterize complex 3D bodies and incorporate them into geodynamic inverse problems. The approach can automatically create an entire ensemble of initial geometries, enabling us to account for uncertainties in imaging data. Furthermore, it allows us to investigate the sensitivity of the model results to geometrical properties and facilitates inverting for them. We demonstrate the method with two examples. A salt diapir in an extending regime and free subduction of an oceanic plate under a continent. In both cases, small differences in the model’s initial geometry lead to vastly different results. Be it the formation of faults or the velocity of plates. Using the salt diapir example, we demonstrate that, given an additional geophysical observation, we are able to invert for uncertain geometric properties. This highlights that geodynamic studies should investigate the sensitivity of their models to the initial geometry and include it in their inversion framework. We make our method available as part of the open-source software geomIO.

The comprehensive understanding of the occurred changes of permafrost, including the changes of mean annual ground temperature (MAGT) and active layer thickness (ALT), on the Qinghai-Tibet Plateau (QTP) is critical to project permafrost changes due to climate change. Here, we use statistical and machine learning (ML) modeling approaches to simulate the present and future changes of MAGT and ALT in the permafrost regions of the QTP. The results show that the combination of statistical and ML method is reliable to simulate the MAGT and ALT, with the root-mean-square error of 0.53°C and 0.69 m for the MAGT and ALT, respectively. The results show that the present (20002015) permafrost area on the QTP is 1.04 × 106 km2 (0.801.28 × 106 km2), and the average MAGT and ALT are -1.35 ± 0.42°C and 2.3 ± 0.60 m, respectively. According to the classification system of permafrost stability, 37.3% of the QTP permafrost is suffering from the risk of disappearance. In the future (20612080), the near-surface permafrost area will shrink significantly under different Representative Concentration Pathway scenarios (RCPs). It is predicted that the permafrost area will be reduced to 42% of the present area under RCP8.5. Overall, the future changes of MAGT and ALT are pronounced and region-specific. As a result, the combined statistical method with ML requires less parameters and input variables for simulation permafrost thermal regimes and could present an efficient way to figure out the response of permafrost to climatic changes on the QTP.

Methane (CH4) hydrate dissociation and CH4 release are potential geohazards currently investigated using X-ray computed tomography (XCT) imaging in laboratory experiments. Image segmentation constitutes an important data processing step for this type of research, but it is often time consuming, computing resource-intensive and operator-dependent. Furthermore, segmentation procedures are frequently tailored for each XCT data set due to differences in image characteristics, such as greyscale contrast variations. To address these issues, an investigation has been carried out using U-Nets, a novel class of Convolutional Neural Network, to segment synchrotron radiation XCT (SRXCT) images of CH4-bearing sand during hydrate formation. Three U-Net deployment methodologies previously untried for this task were assessed: (1) 3D hierarchical, (2) 2D multilabel and (3) RootPainter, a 2D application that implements interactive corrections. Results show high segmentation accuracy, with RootPainter slightly outperforming the alternative approaches. Greyscale contrast between material phases was found to affect segmentation performance, with the lowest metrics corresponding to data exhibiting the lowest contrast. Segmentation accuracy affected derived parameters such as CH4-saturation and porosity, but errors were small compared with gravimetric methods. It was also found that U-Net models trained on low greyscale contrast images could be used to segment higher-contrast data sets and produce accurate 3D visualizations of CH4 distribution, demonstrating model portability. Such portability is anticipated to be advantageous when the segmentation of large XCT data sets needs to be delivered over short timespans.

The drivers of the efficiency in organic carbon (OC) burial are still poorly understood despite their key role in reliable projections of future climate trends. Here we shed new light on this question by presenting paleoclimate time series including OC content in sediments from Lake Veliko jezero, Croatia. The Sr/Ca ratios of the bulk sediment mainly derives from Sr and Ca concentrations of needle like aragonite in Core M1-A and was used as a palaeotemperature and palaeohydrology indicator. Four major and six minor cold and dry events were detected in the 8.3 to 2.6 cal ka BP interval. The combined assessment of Sr/Ca ratios, OC content, C/N ratios, δ13C data, and modelled proxies for palaeoredox conditions and aeolian input reveals that cold and dry climate state promoted anoxic conditions in the lake enhancing preservation of organic matter and leading to increased OC burial efficiency. Our study contributes to that projected future increase of temperature might play an important role in OC burial efficiency of meromictic lakes.

We present a re-examination of mass spectral data obtained from the Pioneer Venus Large Probe Neutral Mass Spectrometer. Our interpretations of differing trace chemical species are suggestive of redox disequilibria in Venus’ middle clouds. Assignments to the data (at 51.3 km) include phosphine, hydrogen sulfide, nitrous acid, nitric acid, carbon monoxide, hydrochloric acid, hydrogen cyanide, ethane, and potentially ammonia, chlorous acid, and several tentative PxOy species. All parent ions were predicated upon assignment of corresponding fragmentation products, isotopologues, and atomic species. The data reveal parent ions at varying oxidation states, implying the presence of reducing power in the clouds, and illuminating the potential for chemistries yet to be discovered. When considering the hypothetical habitability of Venus’ clouds, the assignments reveal a potential signature of anaerobic phosphorus metabolism (phosphine), an electron donor for anoxygenic photosynthesis (nitrite), and major constituents of the nitrogen cycle (nitrate, nitrite, ammonia, and N2).

Sediment grain size links sediment production, weathering, and fining from fractured bedrock on hillslopes to river incision and landscape relief. Yet, models of sediment grain size delivery to rivers remain unconstrained due to a scarcity of field data. We analyzed how bedrock fracture spacing and hillslope weathering influence landscape-scale patterns in surface sediment grain size across gradients of erosion rate and hillslope bedrock exposure in the San Gabriel Mountains (SGM) and northern San Jacinto Mountains (NSJM) of California, USA. Using ground-based structure-from-motion photogrammetry models of 50 bedrock cliffs, we showed that fracture density is ~5× higher in the SGM than the NSJM. 274 point count surveys of surface sediment grain size measured in the field and from imagery show a drainage area control on sediment grain size, with systematic downslope coarsening on hillslopes and in headwater colluvial channels transitioning to downstream fining in fluvial channels. In contrast to prior work and predictions from a hillslope weathering model, grain size does not increase smoothly with increasing erosion rate. For soil-mantled landscapes, sediment grain size increases with increasing erosion rates; however, once bare bedrock emerges on hillslopes, sediment grain size in both the NSJM and SGM becomes insensitive to further increases in erosion rate and hillslope bedrock exposure, and instead reflects fracture spacing contrasts between the NSJM and SGM. We interpret this threshold behavior to emerge in steep landscapes due to efficient delivery of coarse sediment from bedrock hillslopes to channels and the relative immobility of coarse sediment in fluvial channels.

The 2020 Mw 6.8 Elazig earthquake was the largest along the Eastern Anatolian Fault (EAF) in over a century, providing valuable insights into its rupture behavior. We use satellite geodesy and seismology to detail the mainshock rupture, postseismic deformation and aftershocks. The mainshock propagated mostly westwards at 2 km/s from a nucleation point on an abrupt 10° fault bend. Only one end of the rupture corresponds to an established EAF segment boundary, and the earthquake may have propagated into the slip zone of the 1874 M 7.1 Golcuk Golu earthquake. It exhibits a pronounced (80%) shallow slip deficit, only a small proportion of which is recovered by early aseismic afterslip. The slow rupture velocity, shallow slip deficit and low afterslip are characteristic of earthquakes hosted by faults of low-to-intermediate structural maturity, indicating that faults continue to evolve in important ways even as they accrue cumulative off sets of tens of kilometers

Previous studies of wind-blown sand have considered either fully erodible or non-erodible soils, but the transport over sparsely sand-covered soils is still poorly understood. The quantitative modeling of this transport is important for the parametrization of Aeolian processes under low sand availability. Here we show, by means of particle-based numerical simulations, that the Aeolian sand transport rate Q scales with the wind shear velocity u∗ as Q = a.[1 + b . (u∗/u∗t − 1)] .√(d/g) . ρf. (u∗² − u∗t²), where u∗t is the minimal threshold u∗ for sustained transport, d is particle size, g is gravity and ρf is air density, while u∗t and the empirical parameters a and b depend on the sand cover thickness. Our model explains the transition from the quadratic to cubic scaling of Q with u∗ as soil conditions change from fully erodible to rigid and provides constraints for modeling Aeolian transport under low sand availability.

Tropical mountain glaciers are an important water resource and highly impacted by recent climate change. Tropical mountain glaciation also occurred in the recent and deep past, which presents opportunities for better validating paleoclimate simulations in continental interiors and mountainous regions but requires bridging global model scales (100s of km) with the ~ 1–10 km scale of glaciers when paleotopography is poorly known. Here we hindcast tropical mountain glaciation in pre-industrial time by using global climate model meteorology to force standalone simulations in its land component that use high resolution topography to resolve selected tropical mountain glaciers. These simulations underestimate observed equilibrium line altitudes (ELA) by 249 ± 330 m, but the simulated ELA and snow lines capture observed inter-mountain ELA variability. Error in large-scale model precipitation and ELA reconstruction uncertainty are the main contributors to this bias.

We investigate the solar events of late solar cycle 24 in July 2017 observed by a number of spacecraft in the inner heliosphere widely separated in heliolongitude and radial distance. These include spacecraft at L1 point, STEREO-A, near Earth satellites, and MAVEN (near Mars). The GRASP payload onboard Indian GSAT-19 satellite provides a new vantage point for Solar Energetic Particle (SEP) observations near Earth. There were two major Coronal Mass Ejections (CMEs) and a Stream Interaction Region (SIR) event in July 2017, which is a period during the deep descending phase of the historically weak solar cycle 24. The 16 July CME was Earth directed and the 24 July CME was STEREO-A and Mars directed. Earth and Mars were on the opposite sides of the solar disk, while Mars and STEREO-A were aligned with respect to the nominal Parker spiral field. The 24 July event was stronger and wider in heliolongitude. This CME-driven shock had magnetic connectivity to Earth, which produced an SEP event at Earth ~two days later. The spectral indices of the event observed directly at STEREO-A and at the remote location of ACE was found to be similar. The 16 July SIR event was observed by both MAVEN and STEREO-A. Higher particle intensities (a factor of 6 enhancement for 1 MeV protons) are observed by MAVEN (at 1.58 AU) compared to STEREO-A (at 0.96 AU). Also a spectral hardening is observed while comparing the spectral indices at these two locations, indicating proton acceleration at the SIR forward shock during the radial propagation of 0.62 AU in the interplanetary space.

The subduction zone along the northern Tonga Trench has the highest plate convergence rate in the world, but limited records of its seismic and tsunamigenic activities. In 2009, a tsunami generated by an MW 8.1 earthquake doublet caused severe impacts in the region including damage and loss of life on the south shores of Upolu and Savaii Islands, Samoa. Here we use numerical modeling aided by recorded data and eyewitness accounts to evaluate which of the published source models in the Tonga Trench region most suitably represents the 2009 event for use in hazard assessment around Samoa. We show that only a few of the published sources are suitable to reproduce large inundation observed in Samoa and none reproduces runup as high as observed in areas that were most severely impacted on the southeast Upolu coast. The distribution and intensity of inundation is dependent on local topographic and bathymetric features, configuration of coastal geomorphology, and trapping of short-period waves over the reef flats. For one of the sources, comparison of the relative contributions of the normal and thrust faulting components of the doublet to the southeast Upolu inundation indicates that the initial intraplate normal faulting dominated the east-northeastward tsunami propagation and inundation compared with the subsequent interplate thrust faulting. Overall, two key source models are discussed and identified for future refinement.

In steep wildfire-burned terrains, intense rainfall can produce large volumes of runoff that can trigger highly destructive debris flows. The ability to accurately characterize and forecast debris-flow hazards in burned terrains, however, remains limited. Here, we augment the Weather Research and Forecasting Hydrological modeling system (WRF-Hydro) to simulate both overland and channelized flows and assess postfire debris-flow hazards over a regional domain. We perform hindcast simulations using high-resolution weather radar-derived precipitation and reanalysis data to drive non-burned baseline and burn scar sensitivity experiments. Our simulations focus on January 2021 when an atmospheric river triggered numerous debris flows within a wildfire burn scar in Big Sur – one of which destroyed California’s famous Highway 1. Compared to the baseline, our burn scar simulation yields dramatic increases in total and peak discharge, and shorter lags between rainfall onset and peak discharge. At Rat Creek, where Highway 1 was destroyed, discharge volume increases eight-fold and peak discharge triples relative to the baseline. For all catchments within the burn scar, we find that the median catchment-area normalized discharge volume increases nine-fold after incorporating burn scar characteristics, while the 95th percentile volume increases 13-fold. Catchments with anomalously high hazard levels correspond well with post-event debris flow observations. Our results demonstrate that WRF-Hydro provides a compelling new physics-based tool to investigate and potentially forecast postfire hydrologic hazards at regional scales.

Along the lateral margins of floating ice shelves in Greenland and Antarctica, ice flow past confining margins and pinning points is often accompanied by extensive rifting. Rifts in zones of marginal decoupling (“detachment zones’) typically propagate inward from the margins and result in many of Earth’s largest calving events. Velocity maps of detachment zones indicate that flow through these regions is spatially transitioning from confined to unconfined shelf flow. We employ the software package \textit{icepack} to demonstrate that longitudinally decreasing marginal resistance reproduces observed transitions in flow regime, and we show that these spatial transitions are accompanied by near-margin tension sufficient to explain full-thickness rifts. Thus, we suggest that zones of progressive decoupling are a primary control on ice shelf calving. The steadiness of detachment zone positions may be a good indicator of ice shelf vulnerability, with migratory or thinning detachment zones indicating shelves at risk of dynamic speedup and increased fracture.

The grandest geotourism attractions in the southern hemisphere, in the nineteenth century were the siliceous Pink and White Terraces, the lost New Zealand Eighth Wonder of the World. In 1886, the Tarawera eruption buried the terraces. In the absence of a government survey or evidence of their locations; public debate over their survival ensued until the 1940s. Recently, a unique survey was uncovered and led researchers at last to the Terrace locations. Early colonial visitors were told by traditional landowners, that the major White Terrace spring erupted in strong easterly winds. Having researched the Pink and White Terraces for some years, this 1859 report puzzled me, as it did Ferdinand Hochstetter to whom the first report was made in 1859. From previous studies in automotive crankcase ventilation, I could see a potential causal pathway for these east-wind spring eruptions. After examining the topography of the White Terrace spring, embankment and apron: I suggest the puzzling eruptions were a product of three phenomenae: the Venturi and Coandă effects, with Bernoulli’s principle. This paper presents the evidence for the presence of Venturi and Coandă effects at the Lake Rotomahana Basin. More importantly, it discusses how these effects contributed to postulated spring eruptions during the 1886 eruptions; which created so far unexplained water ponding around the Pink, Black and White Terrace locations. These surface waters contribute to the new paradigm for the Rotomahana Basin during the 1886 eruptions; where the topographic changes lead today’s researchers to the lost Terrace locations around the shores of the new Lake Rotomahana.

Mixed siliciclastic and carbonate active orogens are common on Earth’s surface, yet most studies have focused on physical erosion and chemical weathering in silicate-rich landscapes. Relative to purely siliciclastic landscapes, the response of erosion and weathering to uplift may differ in mixed-lithology regions. However, our knowledge of weathering and erosion in mixed carbonate-silicate lithologies is limited and thus our understanding of the mechanistic coupling between uplift, chemical weathering, and the carbon cycle. Here, we partition the denudation fluxes into erosion and weathering fluxes of carbonates and silicates in the Northern Apennine Mountains of Italy—a mixed siliciclastic-carbonate active orogen—using dissolved solutes, the fraction of carbonate sand in sediments, and existing 10Be denudation rates. Erosion fluxes are generally an order of magnitude higher than weathering fluxes and dominate total denudation. The contribution of carbonate and silicate minerals to erosion varies between lithologic units, but weathering fluxes are systematically dominated by carbonates. Silicate weathering may be limited by reaction rates, whereas carbonate weathering may be limited by acidity of the rivers that drain the orogen. Precipitation of secondary calcite from super-saturated streams leads to the loss of up to 90% of dissolved Ca2+ from carbonate-rich catchments. Thus, in the weathering zone, [Ca2+] is exceptionally high, likely driven by high soil pCO2; however, re-equilibration with atmospheric pCO2 in rivers converts solutes back into solid grains that become part of the physical denudation flux. Limits on weathering in this landscape therefore differ between the subsurface weathering zone and what is exported by rivers.

Images from the Mars Science Laboratory (MSL) mission of lacustrine sedimentary rocks of Vera Rubin ridge on “Mt. Sharp” in Gale crater, Mars, have shown stark color variations from red to purple to gray. These color differences cross-cut stratigraphy and are likely due to diagenetic alteration of the sediments after deposition. However, the chemistry and timing of these fluid interactions is unclear. Determining how diagenetic processes may have modified chemical and mineralogical signatures of ancient martian environments is critical for understanding the past habitability of Mars and achieving the goals of the MSL mission. Here we use visible/near-infrared spectra from Mastcam and ChemCam to determine the mineralogical origins of color variations in the ridge. Color variations are consistent with changes in spectral properties related to the crystallinity, grain size, and texture of hematite. Coarse-grained gray hematite spectrally dominates in the gray patches and is present in the purple areas, while nanophase and fine-grained red crystalline hematite are present and spectrally dominate in the red and purple areas. We hypothesize that these differences were caused by grain size coarsening of hematite by diagenetic fluids, as observed in terrestrial analogs. In this model, early primary reddening by oxidizing fluids near the surface was followed during or after burial by bleaching to form the gray patches, possibly with limited secondary reddening after exhumation. Diagenetic alteration may have diminished the preservation of biosignatures and changed the composition of the sediments, making it more difficult to interpret how conditions evolved in the paleolake over time.

Large earthquakes rapidly denude hillslopes by triggering thousands of coseismic landslides. The sediment produced by these landslides is initially quickly mobilised from the landscape by an interconnected cascade of processes. This cascade can dramatically but briefly enhance local erosion rates. Hillslope and channel processes, such as landsliding and debris flows, interact to influence the total mass, calibre, and rate of sediment transport through catchments. Calculating the sediment budget of an earthquake lends insight into the nature of these interactions. Using satellite imagery derived landslide inventories, channel surveys and a literature review combined with a Monte Carlo simulation approach we present a constrained sediment budget of the first decade after the 2008 Mw7.9 Wenchuan earthquake. With this sediment budget we demonstrate that debris flows are dominant process for delivering sediment into channels and that large volumes of sediment remain in the landscape. In our study area over 88% (469 Mega tonnes) of the coseismically generated sediment remains on the hillslopes in 2018. Of the 12% of the sediment that was mobilised, 69% (40.7 14 Mt) was mobilised by debris flows. Despite the large proportion of sediment remaining on the hillslope, the frequency of debris flows declined significantly over our observation period. The reduction in debris-flow frequency is not correlated to reductions in the frequency of triggering storms, suggesting changes in the mechanical properties of hillslope sediment may drive this observation. The stabilisation of coseismically generated sediment greatly extends its residence time and may influence catchment sediment yields for centuries or millennia.

Unless humanity achieves United Nations Sustainable Development Goals (SDGs) by 2030 and restores the relatively stable climate of pre-industrial CO2 levels (as early as 2110), species extinctions, starvation, drought/floods, and violence will exacerbate mass migrations. This paper presents conceptual designs and techno-economic analyses to calculate sustainable limits for growing high-protein seafood and macroalgae-for-biofuel. We review the availability of wet solid waste and outline the mass balance of carbon and plant nutrients passing through a hydrothermal liquefaction process. The paper reviews the availability of dry solid waste and dry biomass for bioenergy with CO2 capture and storage (BECCS) while generating Allam Cycle electricity. Sufficient wet-waste biomass supports quickly building hydrothermal liquefaction facilities. Macroalgae-for-biofuel technology can be developed and straightforwardly implemented on SDG-achieving high protein seafood infrastructure.). The analyses indicate a potential for (1) 0.5 billion tonnes/yr of seafood; (2) 20 million barrels/day of biofuel from solid waste; (3) more biocrude oil from macroalgae than current fossil oil; and (4) sequestration of 28 to 38 billion tonnes/yr of bio-CO2. Carbon dioxide removal (CDR) costs are between 25−33% of those for BECCS with pre-2019 technology or the projected cost of air-capture CDR.

A flowslide overriding liquefied substrate can vastly enhance its disaster after failure initiation, due to rapid velocity and long-runout distance during landslides mobilized into flows. It is crucial to provide improved understanding to the mechanism of these catastrophic flowslides for hazard mitigation and risk assessment. This study focuses on the Saleshan landslide of Gansu in China, which is a typically catastrophic flowslide overrode a liquefied sand substrate. Geomorphologic and topographic maps along with analysis of seismic signals confirm its dynamic features and mobilized behaviors. ERT surveying detected abundant groundwater in the landslide, which is fundamental to its rapid long-runout distance. Particle size distributions and triaxial shear behaviors affirmed more readily liquefied behavior of superficial loess and underlying alluvial sand than red soil sandwiched them. We also examined the liquefaction susceptibility of the alluvial sand under loading impact at undrained and drained conditions. The alluvial sand is readily liquefied in the undrained condition while it is difficult at drained condition due to rapid water pore pressure dissipation. The results showed that the landslide experienced a sudden transformation from slide on the steep slope where it originated to flow on a nearly flat terrace with abundant groundwater that it overrode. This transformation can be attributed to the liquefied alluvial sand substrate enhancing the whole landslide body mobility. Along with recent, similar findings from landslides worldwide, substrate liquefaction may present a widespread, significant increase in landslide hazard and consequent mobility and our study reveals conditions necessary for this phenomenon to occur.

The seismic activity of the middle strand of the North Anatolian Fault (MNAF), Northwestern Turkey, is debated because of its quiescence during the instrumental period, in contrast to a significant historical activity documented by several chronicles over the last two millennia. Here, we focus on Lake Iznik, bordered by the MNAF, to get a new insight into its long-term seismicity and its tectonic setting. The study of lacustrine sediment cores reveals fourteen earthquake-induced turbidites since their ages correspond to seismic events during the past two millennia. Bathymetry and high-resolution seismic reflection data allow describing two hitherto unknown subaquatic active fault structures (the South Boyalica and Iznik faults) that belong to the MNAF system. Sediment cores sampled on both sides of the Iznik Fault document an event deposit and a sedimentary unit vertically offset of ~ 40 cm interpreted as the last rupture during the 1065 CE destructive earthquake. Older events are supposed on this fault more than a thousand years ago. Further studies will help to estimate the horizontal coseismic offset of this oblique-slip fault and the calendar of older ruptures. The current seismic gap of thousand years on this segment greatly increases the seismic hazard in this region and must be considered in the seismic risk assessment of the NAF system.

Western Jezero crater of Mars exposes smooth- and rough-surfaced plains that bound a steep-sided fan-shaped plateau (i.e., western Jezero delta) in the west. The two plain terrains have a gradational contact and their end-member occurrences can be defined by the absence (smooth-surfaced) and presence (rough-surfaced) of littered surficial boulders and depressions. Early researchers interpret the plain terrains as morphological expression of volcanic flow and aeolian, fluvial, or lacustrine deposition, but these hypotheses have not been tested rigorously via detailed mapping. Here we show results of HiRISE-based mapping that reveals four landform units hosted by both smooth- and rough-surfaced terrains: (1) polygonal networks of double-ridged grooves that are 2-4 m wide, up to ~1700 m long, and spaced > ~100 m, (2) reticulate networks of grooves spaced mostly < ~10 m, (3) undulating surfaces hosting variously shaped depressions, and (4) NE-trending boulder-bearing ridges (~10 m wide and 70-300 m long) locally displaying NE-pointing streamlined shapes. Our mapping shows that the NE-trending boulder ridges formed first followed sequentially by the formation of depressions, double-ridged grooves, and reticulate grooves. None of the above observations can be explained as a whole by volcanic emplacement and/or earlier proposed aeolian, fluvial, and lacustrine depositional processes. Guided by Earth analogues, we interpret the streamlined boulder ridges as subglacial flutes, depressions including most circular pits with raised rims as kettle holes and/or thermokarsts, polygonal networks of double-ridged grooves as crevasse-filled ice-pressed moraine ridges and the polygonal pattern was inherited from the fractured glacier, and reticulate grooves as desiccation cracks during the final drying of glacial deposits at the end of a martian ice age.

Axial Seamount is a basaltic hot spot volcano with a summit caldera at a depth of ~1500 m below sea level, superimposed on the Juan de Fuca spreading ridge, giving it a robust and continuous magma supply. Axial erupted in 1998, 2011, and 2015, and is monitored by a cabled network of instruments including bottom pressure recorders and seismometers. Since its last eruption, Axial has re-inflated to 85-90% of its pre-eruption level. During that time, we have identified eight discrete, short-term deflation events of 1-4 cm over 1-3 weeks that occurred quasi-periodically, about every 4-6 months between August 2016 and May 2019. During each short-term deflation event, the rate of earthquakes dropped abruptly to low levels, and then did not return to higher levels until reinflation had resumed and returned near its previous high. The long-term geodetic monitoring record suggests that the rate of magma supply has varied by an order of magnitude over decadal time scales. There was a surge in magma supply between 2011-2015, causing those two eruptions to be closely spaced in time and the supply rate has been waning since then. This waning supply has implications for eruption forecasting and the next eruption at Axial still appears to be 4-9 years away. We also show that the number of earthquakes per unit of uplift has increased exponentially with total uplift since the 2015 eruption, a pattern consistent with a mechanical model of cumulative rock damage leading to bulk failure during magma accumulation between eruptions.