The North Anatolian Fault (NAF) has produced numerous major earthquakes. After decades of quiescence, the Mw 6.8 Elazig earthquake (January 24, 2020) has recently reminded us that the East Anatolian Fault (EAF) is also capable of producing significant earthquakes. To better estimate the seismic hazard associated with these two faults, we jointly invert Interferometric Synthetic Aperture Radar (InSAR) and GPS data to image the spatial distribution of interseismic coupling along the eastern part of both the North and East Anatolian Faults. We perform the inversion in a Bayesian framework, enabling to estimate uncertainties on both long-term relative plate motion and coupling. We find that coupling is high and deep (0-20 km) on the NAF and heterogeneous and superficial (0-5 km) on the EAF. Our model predicts that the Elazig earthquake released between 200 and 250 years of accumulated moment, suggesting a bi-centennial recurrence time.

Experiment and observation have established the centrality of oxygen fugacity (fO2) to determining the course of igneous differentiation, and so the development and application of oxybarometers have proliferated for more than half a century. The compositions of mineral, melt, and vapor phases determine the fO2 that rocks record, and the activity models that underpin calculation of fO2 from phase compositions have evolved with time. Likewise, analytical method development has made new sample categories available to oxybarometric interrogation. Here we compile published analytical data from lithologies that constrain fO2 (n=860 volcanic rocks - lavas and tephras and n=326 mantle lithologies- the majority peridotites) from ridges, back-arc basins, forearcs, arcs, and plumes. Because calculated fO2 varies with choice of activity model, we re-calculate fO2 for each dataset from compositional data, applying the same set of activity models and methodologies for each data type. Additionally, we compile trace element concentrations (e.g. vanadium) which serve as an additional fO2-proxy. The compiled data show that, on average, volcanic rocks and mantle rocks from the same tectonic setting yield similar fO2s, but mantle lithologies span a much larger range in fO2 than volcanics. Multiple Fe-based oxybarometric methods and vanadium partitioning vary with statistical significance as a function of tectonic setting, with fO2 ridges < back arcs < arcs. Plume lithologies are more nuanced to interpret, but indicate fO2s  ridges. We discuss the processes that may shift fO2 after melts and mantle lithologies physically separate from one another. We show that the effects of crystal fractionation and degassing on the fO2 of volcanics are smaller than the differences in fO2 between tectonic settings and that effects of subsolidus metamorphism on the fO2 values recorded by mantle lithologies remain poorly understood. Finally, we lay out challenges and opportunities for future inquiry.

Modelling the planetary heat transport of small bodies in the early Solar System allows us to understand the geological context of meteorite samples. Conductive cooling in planetesimals is controlled by thermal conductivity, heat capacity, and density, which are functions of temperature (T). We investigate if the incorporation of the T-dependence of thermal properties and the introduction of a non-linear term to the heat equation could result in different interpretations of the origin of different classes of meteorites. We have developed a finite difference code to perform numerical models of a conductively cooling planetesimal with T-dependent properties and find that including T-dependence produces considerable differences in thermal history, and in turn the estimated timing and depth of meteorite genesis. We interrogate the effects of varying the input parameters to this model and explore the non-linear T-dependence of conductivity with simple linear functions. Then we apply non-monotonic functions for conductivity, heat capacity and density fitted to published experimental data. For a representative calculation of a 250 km radius pallasite parent body, T-dependent properties delay the onset of core crystallisation and dynamo activity by ~40 Myr, approximately equivalent to increasing the planetary radius by 10 %, and extend core crystallisation by ~3 Myr. This affects the range of planetesimal radii and core sizes for the pallasite parent body that are compatible with paleomagnetic evidence. This approach can also be used to model the T-evolution of other differentiated minor planets and primitive meteorite parent bodies and constrain the formation of associated meteorite samples.

Magmas readily react with their surroundings, which may be other magmas or solid rocks. Such reactions are important in the chemical and physical evolution of magmatic systems and the crust, for example, in inducing volcanic eruptions and in the formation of ore deposits. In this contribution, we conceptually distinguish assimilation from other modes of magmatic interaction and discuss and review a range of geochemical (+/- thermodynamical) models used to model assimilation. We define assimilation in its simplest form as an end-member mode of magmatic interaction in which an initial state (t0) that includes a system of melt and solid wallrock evolves to a later state (tn) where the two entities have been homogenized. In complex natural systems, assimilation can refer more broadly to a process where a mass of magma wholly or partially homogenizes with materials derived from wallrock that initially behaves as a solid. The first geochemical models of assimilation used binary mixing equations and then evolved to incorporate mass balance between a constant-composition assimilant and magma undergoing simultaneous fractional crystallization. More recent tools incorporate energy and mass conservation in order to simulate changing magma composition as wallrock undergoes partial melting. For example, the Magma Chamber Simulator utilizes thermodynamic constraints to document the phase equilibria and major element, trace element, and isotopic evolution of an assimilating and crystallizing magma body. Such thermodynamic considerations are prerequisite for understanding the importance and thermochemical consequences of assimilation in nature, and confirm that bulk assimilation of large amounts of solid wallrock is limited by the enthalpy available from the crystallizing resident magma. Nevertheless, the geochemical signatures of magmatic systems-although dominated for some elements (particularly major elements) by crystallization processes-may be influenced by simultaneous assimilation of partial melts of compositionally distinct wallrock.

When rivers collide, complex three-dimensional coherent flow structures are generated along the confluence’s mixing interface. These structures play important roles in mixing streamborne pollutants and suspended sediment and have considerable bearing on the morphology and habitat quality of the postconfluent reach. A particular structure of interest - streamwise orientated vortices (SOVs) - were first detected in numerical simulations to form in pairs, one on each side of the mixing interface rotating in the opposite sense of the other. Since, it has proven difficult to detect SOVs in situ with conventional pointwise velocimetry instrumentation. Despite the lack of clear evidence to confirm their existence, SOVs are nevertheless considered important drivers of mixing and sediment transport processes at confluences. Additionally, their causal mechanisms are also not fully known which hinders a complete conceptual understanding of these processes. To address these gaps, we analyze observations of strongly coherent SOVs filmed in aerial drone video of a mesoscale confluence with a stark turbidity contrast between its tributaries. Eddy-resolved modeling demonstrates the SOVs’ dynamics could only be accurately reproduced when a density difference (Δρ) was imposed between the tributaries (Δρ = 0.5 kg/m$^{3}$) – providing compelling evidence the observed SOVs are indeed a density-driven class of SOV. This work confirms that SOVs exist, expands understanding of their generative processes and highlights the important role of small density gradients (e.g., less than 0.5 kg/m3) on river confluence hydrodynamics.

Antarctic ice sheets play an important role in global sea-levels and climate changes. Snowmelt information with high spatial resolution on the surface of ice sheets is of great significance to the study of global climate change. Currently, the spatial resolution of snowmelt detection results based on low-frequency data from microwave radiometers is low, and accurate freeze-thaw changes cannot be obtained. The spatial resolution of Advanced Microwave Scanning Radiometer-2(AMSR-2)89GHz data is at least twice that of other microwave channels, but vulnerable to atmospheric water vapour. This paper proposes a method to detect snowmelt on the Antarctic ice sheet based on 89GHz data. First, according to the stable relationship of the polarization ratio(PR)of 89GHz and 36GHz data under clear, cloudless weather, the affected 89GHz data were selected. Then, the functional relationship between 36 GHz data and the unaffected 89 GHz data was obtained. Finally, the modified 89 GHz data were applied to snowmelt detection on the Antarctic ice sheet. The average detection accuracy of this method in six automatic weather stations was 91%, while the average detection accuracy of the cross-polarized gradient ratio algorithm(XPGR)was 74%. The experimental results show that the modified 89GHz data have a high accuracy in detecting snowmelt in Antarctic ice sheets.

We developed a flexible finite-fault inversion method for teleseismic P waveforms to obtain a detailed rupture process of a complex multiple-fault earthquake. We estimate the distribution of potency-rate density tensors on an assumed model plane to clarify rupture evolution processes, including variations of fault geometry. We applied our method to the 23 January 2018 Gulf of Alaska earthquake by representing slip on a projected horizontal model plane at a depth of 33.6 km to fit the distribution of aftershocks occurring within one week of the mainshock. The obtained source model, which successfully explained the complex teleseismic P waveforms, shows that the 2018 earthquake ruptured a conjugate system of N-S and E-W faults. The spatiotemporal rupture evolution indicates irregular rupture behavior involving a multiple-shock sequence, which is likely associated with discontinuities in the fault geometry that originated from E-W sea-floor fracture zones and N-S plate-bending faults.

Drilling and multi-stage hydraulic fracturing bring a large amount of water into the formation, and clay-bearing shale reservoirs interact with water, which may lead to reduction of gas production, attenuation of fracturing effects, and even wellbore instability. Because of the complex fabric of shale, a thorough understanding of changes in shale micromechanics and corresponding mechanisms when exposed to water remains unclear. In this work, representative terrestrial and marine shale samples were selected for experiments based on clay enrichment. Then, contact resonance (CR) technique was performed to characterize micromechanics of shale after exposure to water. Visual phenomena provided by environmental scanning electron microscopy (ESEM) assisted to explain the underlying mechanisms. It was found that the hydration effect lowered both the storage modulus and stiffness of samples, but with different contributions from brittle minerals and clay, as well as variations depending on bedding plane orientation. Owing to the difference in composition, terrestrial shale exhibited stronger water sensitivity and anisotropy, with a general 15%-25% decrease in modulus, while marine shale changed relatively little (-5%-15%). Moreover, microscopic observation experiments revealed that complex interaction mechanisms may have existed that produced the mechanical changes. The reduction of capillary force and the interlaminar swelling of clay particles after water adsorption weakened the strength-related behavior of shale. However, the swelling-caused confining effect or void space closure during the water imbibition process might have offset this weakening effect, and even increased mechanical properties. At mesoscale, excessive shrinkage caused the growth of micro-cracks, which significantly attenuated overall mechanical behavior.

In the Arctic, the spatial distribution of boreal forest cover and soil profile transition characterizing the taiga-tundra ecological transition zone (TTE) is experiencing an alarming transformation. The SIBBORK-TTE model provides a unique opportunity to predict the spatiotemporal distribution patterns of vegetation heterogeneity, forest structure change, arctic-boreal forest interactions, and ecosystem transitions with high resolution scaling across broad domains. Within the TTE, evolving climatological and biogeochemical dynamics facilitate moisture signaling and nutrient cycle disruption, i.e. permafrost thaw and nutrient decomposition, thereby catalyzing land cover change and ecosystem instability. To demonstrate these trends, in situ ground measurements for active layer depth were collected to cross-validate below-ground-enhanced modeled simulations from 1996-2017. Shifting trends in permafrost variability (i.e. active layer depth) and seasonality were derived from model results and compared statistically to the in situ data. The SIBBORK-TTE model was then run to project future below-ground conditions utilizing CMIP6 scenarios. Upon visualization and curve-integrated analysis of the simulated freeze-thaw dynamics, the calculated performance metric associated with annual maximum active layer depth rate of change yielded 76.19%. Future climatic conditions indicate an increase in active layer depth and shifting seasonality across the TTE. With this novel approach, spatiotemporal variation of active layer depth provides an opportunity for identifying climate and topographic drivers and forecasting permafrost variability and earth system feedback mechanisms.

The Gondwana Late Paleozoic Ice Age is probably best represented by the Dwyka Group in South Africa. Striated and grooved surfaces or pavements are commonly considered to be subglacially formed, as are diamictites which have been interpreted as in situ or reworked tillites. These interpretations were tested by investigation of outcrops in formerly well studied areas, throughout South Africa. Detailed analyses focused on striated surfaces/pavements and surface microtextures on quartz sand grains in diamictites. The sedimentological context of four pavements, interpreted to be glaciogenic, display features commonly associated with sediment gravity flows, rather than glaciation. A total of 4271 quartz sand grains were subsampled from outcrops that are mainly considered to be tillites formed by continental glaciation. These grains, analyzed by SEM, do not demonstrate the characteristic surface microtextures combinations of fracturing and irregular abrasion associated with Quaternary glacial deposits, but mainly a mix of surface microtextures associated with multicyclical grains. The Dwyka Group diamictites warrant reinterpretation as non-glacial sediment gravity flow deposits.

The triggering of large earthquakes on a fault hosting aseismic slip or, conversely, the triggering of slow slip events (SSE) by passing seismic waves involves seismological questions with important hazard implications. Just a few observations plausibly suggest that such interactions actually happen in nature. In this study we show that three recent devastating earthquakes in Mexico are likely related to SSEs, describing a cascade of events interacting with each other on a regional scale via quasi-static and/or dynamic perturbations. Such interaction seems to be conditioned by the transient memory of Earth materials subject to the “traumatic” stressing produced by the seismic waves of the great 2017 (Mw8.2) Tehuantepec earthquake, which strongly disturbed the aseismic slip beating over a 650 km long segment of the subduction plate interface. Our results imply that seismic hazard in large populated areas is a short-term evolving function of seismotectonic processes that are often observable.

In this study, flume experiments were conducted under conditions where alternate bars occur, develop, and migrate, to understand the existence and scale of the spatial distribution of the migrating speed of alternate bars and their dominant physical quantities. In the flume experiment, the bed level and water level during the development of alternate bars were measured with high frequency and high spatial resolution. By comparing the geometric variation of the bed shape, the results showed that the migrating speed of the alternate bars is spatially distributed and changes with time. Next, to quantify the spatial distribution of the migrating speed of the alternate bars, a hyperbolic partial differential equation for the bed level and an calculating equation the migrating speed based on the advection term of the same equation were derived. Subsequently, the derived equation was shown to be applicable by comparing it with the measurements obtained in the flume experiments described above. The migrating speed of the alternate bars was calculated using above formulas, and it was found to have a spatial distribution that changed with the development of the alternate bars over time. The mathematical structure of the equation showed that the three dominant physical quantities of the migrating speed are the particle size, Shields number, and energy slope. In addition, our method is generally applicable to actual rivers, where the scale and hydraulic conditions are different from those in the flume experiments.

Mars’ controversial hypothesized ocean shorelines have been found to deviate significantly from an expected equipotential surface. While multiple deformation models have been proposed to explain the wide range of elevations, here we show that the historical locations used in the literature and in these models vary widely. We find that the most commonly used version of the Arabia Level does not follow the originally described contact and can deviate laterally by ~500 km in Deuteronilus Mensae. A meta-analysis of different published maps shows that, globally, the minimum lateral offsets between the locations of the putative Arabia and Deuteronilus shorelines vary by an average of 141±142 km and 180±177 km, respectively. This leads to mean elevations of the Arabia Level that vary by up to 2.2 km between different mappings, and topographic ranges within each global mapping ranging from 2.7 to 7.7 km. The younger Deuteronilus Level has less topographic variation as it largely follows a formal contact (the Vastitas Borealis Formation) within the relatively flat northern plains. Given the high variance in position (spatial and topographic) of the maps, the use of such data and conclusions based on them are potentially problematic.

The hydrological quantities governing the generation of riverbed waves (formed spontaneously on the bottoms of rivers) have been elucidated through geomorphological methods, laboratory experiments, stability analyses, numerical analyses, and other research methods.Recently, numerical analysis was performed with a fine spatial resolution.However, numerical analysis cannot always describe the real phenomena because it is based on assumptions.Therefore, understanding the physical phenomena by measurements with the same resolution as the numerical analysis is necessary.Measurement data with high resolution enable the construction of a duplicate of the measurement target on a computer, called a “digital twin”.To construct a digital twin of the process of riverbed wave generation and development, the geometries of the water surface and the river bottom must be measured simultaneously.We developed and verified a measurement method for the construction of a digital twin during the generation and development of riverbed waves.The measurement system uses two cameras and a line laser to simultaneously measure the water surface and river bottom.Accurate refraction correction at the water surface is possible by acquiring the shape of the water surface, allowing the bottom shape to be determined by geometric processing.The method provides submillimeter-accurate measurements of the water surface and bottom with a spatial resolution of 0.95 cm longitudinally and 0.038 cm transversely in a 12 m $\times$ 0.45 m channel and takes only one minute per measurement.This method can provide measurement results that contribute to the understanding of the formation and development of riverbed waves.

Coarse-grained quartz veins from the Prijakt Nappe (Austroalpine Unit, Schober Mountains, Eastern Alps), that formed under amphibolite facies conditions, were overprinted by lower greenschist facies deformation. During overprinting, subgrain rotation (SGR) recrystallization was the dominant mechanism assisting the evolution from protomylonite to (ultra)mylonite. The initial Ti-concentration [Ti] (3.0-4.7 ppm) and corresponding cathodoluminescence (CL) signature of the quartz vein crystals were reset to different degrees mainly depending on the availability of fluids and their partitioning across the microstructure. The amount of strain played a subordinate role in resetting. In recrystallized aggregates the most complete re-equilibration ([Ti] of 0.2-0.6 pm) occurred in strain shadows surrounding quartz porphyroclasts, acting as fluid sinks, and in localized shear bands that channelized fluid percolation. We applied a correlative multi-analytical workflow using optical and electron microscopy methods (e.g. electron backscatter diffraction and cathodoluminescence) in combination with secondary ion mass spectroscopy for [Ti] measurement. The most efficient [Ti] resetting mainly occurs along wetted high angle boundaries (misorientation angle >10-15°), and to a minor extend (partial resetting) along dry low angle boundaries (<10-15°). This key-study prove for the first time that pure subgrain rotation recrystallization in combination with dissolution-precipitation under retrograde condition is able to provide microstructural sites to apply the TitaniQ geothermobarometer at deformation temperatures down to 300-350 °C provided that information on pressure and Ti-activity is available.

Interpreting seismo-acoustic signals is critical for assessing and characterizing changes in volcanic vents and has implications for interpreting volcanic unrest. This is especially relevant for Stromboli volcano (Italy), an active stratovolcano with a complex plumbing system, continuous activity, and recurring paroxysms. Stromboli is known for its consistent Strombolian style of eruption, multiple active vents on its crater terrace, and for occasional structural modifications including explosive excavation and/or collapsing craters due to near-surface changes to the plumbing system. This study addresses a single localized collapse of the crater terrace, occurring in May of 2019, when one of Stromboli’s vents changed from a pronounced hornito to a pit crater, resulting in a shift in eruption style at this vent from jetting to Strombolian. The days before and after this transition were recorded with eight infrasound sensors and three seismic geophones located on the crater terrace. We investigate the seismo-acoustic timing of these signals as well as the ratio between seismic and acoustic energy to identify changes associated with eruptive signals and associated variations in location of the eruptive sources. This work highlights the effectiveness of seismo-acoustic data analysis, provides insight into Stromboli’s structural modifications, and builds a foundation for focused analysis of seismo-acoustic signals associated with Stromboli and other open-vent volcanic systems.

The main cause of tsunamis is large subduction zone earthquakes with seismic magnitudes Mw > 7, but submarine volcanic processes can also generate tsunamis. At the submarine Sumisu caldera in the Izu–Bonin arc, moderate-sized earthquakes with Mw < 6 occur almost once a decade and cause meter-scale tsunamis. The source mechanism of the volcanic earthquakes is poorly understood. Here we use tsunami and seismic data for the recent 2015 event to show that abrupt uplift of the submarine caldera, with a large brittle rupture of the ring fault system due to overpressure in its magma reservoir, caused the earthquake and tsunami. This submarine trapdoor faulting mechanism can efficiently generate tsunamis due to large vertical seafloor displacements, but it inefficiently radiates long-period seismic waves. Similar seismic radiation patterns and tsunami waveforms due to repeated earthquakes indicate that continuous magma supply into the caldera induces quasi-regular trapdoor faulting. This mechanism of tsunami generation by submarine trapdoor faulting underscores the need to monitor submarine calderas for robust assessment of tsunami hazards.

On 12 January 2020, Taal volcano, Philippines, erupted after 43 years of repose, affecting more than 500,000 people. Using interferometric synthetic aperture radar (InSAR) data, we present the complete pre- to post-eruption analyses of the deformation of Taal. We find that: 1) prior to eruption, the volcano experienced long-term deflation followed by short-term inflation, reflecting the depressurization-pressurization of its ~5 km depth magma reservoir; 2) during the eruption, the magma reservoir lost a volume of 0.531 +/- 0.004 km^3 while a 0.643 +/- 0.001 km^3 lateral dike was emplaced; and 3) post-eruption analyses reveal that the magma reservoir started recovery approximately 3 weeks after the main eruptive phase. We propose a conceptual analysis explaining the eruption and address why, despite the large volume of magma emplaced, the dike remained at depth. We also report the unique and significant contribution of InSAR data during the peak of the crisis.

The extent of the fault damage zone remains an outstanding challenge confounding attempts to assess rock mass physical and mechanical properties, the effects on landscape evolution and slope stability, and to delineate safe places for human occupation and infrastructure development. Quantifying the relationship between faulting and the spatial geometrical and mechanical characteristics of a rock mass controlled by faulting is difficult, mainly because of varying lithology and rock mass characteristics, the effects of topography and vegetation and local erosion of weaker rock mass. Recent technological developments including Unmanned Aerial Vehicles, terrestrial laser scanning, photogrammetry and point cloud analysis software tools greatly enhance our ability to investigate the issues using the Yarlung Tsangpo (YLTP) Fault of southern Tibet as a case study where ideal geological conditions exist to investigate the relationship. In this study, the procedures, investigation approaches, evidence and criteria for defining the threshold distance for damage zones of YLTP Fault of southern Tibet were studied quantitatively by combining the spatial variations of fracture density, rock mass strength, rockfall inventory and previous thermal evidence. The results have been compared with published data from the evidence of thermal effects related to the exactly the same fault and show a good match between internal thermal action and rock mass physical and mechanical properties controlled by the same faulting. The extent of threshold distance of damage zone of the YLTP Fault is estimated as 5.9±0.6km. Within the damage zone, fracture density and cohesion of the rock mass show power curve relations with distance from the YLTP Fault. The internal dynamic action of fault controls rock mass physical and mechanical properties in the study area. The fault first affects the characteristics of rock mass structures, and then the orientation of the rock structures influences the stability of slope leading to rockfall.

Ancient exhumed accretionary complexes are sometimes associated with high-pressure–low-temperature (HP–LT) metamorphic rocks, such as psammitic schists, which are derived from sandy trench-fill sediment. At accretionary margins, sandy trench-fill sediments are rarely subducted to the depth of HP metamorphism because they are commonly scraped off at the frontal wedge. This study uses sandbox analogue experiments to investigate the role of seafloor topography in the transport of trench-fill sediment to depth during subduction. The experiments were conducted with a detached, rigid backstop to allow a topographic high (representing a seamount) to be subducted through a subduction channel. In experiments without topographic relief, progressive thickening of the accretionary wedge pushed the backstop down, leading to a stepping down of the décollement, narrowing the subduction channel, and underplating the wedge with subducting sediment. In contrast, in experiments with a topographic high, the subduction of the topographic high raised the backstop, leading to a stepping up of the décollement and widening of the subduction channel. These results suggest that the subduction of topographic relief is a possible mechanism for the transport of trench-fill sediment from the trench to HP environments through a subduction channel. A sufficient supply of sediment to the trench and topographic relief on the subducting oceanic plate might enable trench-fill sediment to be accreted at various depths and deeply subducted to become the protoliths of HP–LT metamorphic rocks.

Evidence for tectonic activity on Titan is provided by the presence of eroded mountain ranges. Xanadu is an equatorial region of Titan characterized by a complex topography, even though overall it has a lower average elevation compared to its surroundings. We investigated Xanadu’s southwestern margin, a part of the region which is comprised of heavily eroded and rugged terrains to the north and east and of smoother, more uniform terrains to the west and south. The central portions of southwestern Xanadu are characterized by an extensive fluvial network. The presence of such a distinctive feature was the main reason motivating the study of this area, given its potential to provide tectonic indications. Through detailed geomorphological mapping (map scale 1:700,000) on Synthetic Aperture Radar (SAR) data and analysis of both fluvial drainage patterns and Digital Terrain Models (DTMs), we identified several putative tectonic structures in this area: normal faulting to the west and east, thrust faulting to the north, small-scale strike-slip faulting in its central parts.Pull-apart basins are depressions bounded by both dip-slip faults and by (overlapping and/or bending) segments of a major transcurrent fault, i.e., they are basins generated in transtensional tectonic settings. We propose that central southwestern Xanadu is a pull-apart basin, bordered by both normal and thrust faults and formed by transtensional tectonics, which we consider to be the most recent tectonic phase active in this area. This basin is characterized by small-scale strike-slip faulting within it, on which a fluvial network has subsequently imposed.

How and when plate tectonics initiated remain uncertain. In part, this is because many signals that have been interpreted as diagnostic of plate tectonics can be alternatively explained via hot stagnant-lid tectonics. One such signal involves early Archean phaneritic ultramafic rocks. In the Eoarchean Isua supracrustal belt of southwestern Greenland, some ultramafic rocks have been interpreted as tectonically-exhumed mantle during Eoarchean subduction. To explore whether all Archean phaneritic ultramafic rocks originated as cumulate and/or komatiite – i.e., without requiring plate tectonics – we examined the petrology and geochemistry of such rocks in the Isua supracrustal belt and the Paleoarchean East Pilbara Terrane of northwestern Australia, with Pilbara ultramafic rocks interpreted as representative of rocks from non-plate tectonic settings. We found that Pilbara ultramafic samples have relict cumulate textures, relative enrichment of whole-rock Os, Ir, and Ru versus Pt and Pd, and spinel with variable TiO2, relatively consistent Cr#, and variable and low Mg#. Similar geochemical characteristics also occur in variably altered Isua ultramafic rocks. We show that Isua and Pilbara ultramafic rocks should have interacted with low Pt and Pd melts generated by sequestration of Pd and Pt into sulphide and/or alloy during magma generation or crystallization. Such melts cannot have interacted with a mantle wedge. Furthermore, altered mantle rocks and altered cumulates could have similar rock textures and whole-rock geochemistry such that they may not distinguish mantle from cumulate. Our findings suggest that depleted mantle interpretations are not consistent with geochemistry and/or rock textures obtained from Isua and Pilbara ultramafic rocks. Instead, cumulate textures of Pilbara samples, whole-rock Pt and Pd concentrations, and spinel geochemistry of Isua and Pilbara ultramafic rocks support cumulate origins and metasomatism involving co-genetic melts that formed in hot stagnant-lid settings. Collectively, these findings permit ≤ 3.2 Ga initiation of plate tectonics on Earth.

Rockfalls generate seismic signals that can be used to detect and monitor rockfall activity. Event locations can be estimated on the basis of arrival times, amplitudes or polarization of these seismic signals. However, surface topography variations can significantly influence seismic wave propagation and hence compromise results. Here, we specifically use the signature of topography on the seismic signal to better constrain the source location. Seismic impulse responses are predicted using Spectral Element based simulation of 3D wave propagation in realistic geological media. Subsequently, rockfalls are located by minimizing the misfit between simulated and observed inter-station energy ratios. The method is tested on rockfalls at Dolomieu crater, Piton de la Fournaise volcano, Reunion Island. Both single boulder impacts and distributed granular flows are successfully located, tracking the complete rockfall trajectories by analyzing the signals in sliding time windows. Results from the highest frequency band (here 13-17\,Hz) yield the best spatial resolution, making it possible to distinguish detachment positions less than 100\,m apart. By taking into account surface topography, both vertical and horizontal signal components can be used. Limitations and the noise robustness of the location method are assessed using synthetic signals. Precise representation of the topography controls the location resolution, which is not significantly affected by the assumed impact direction. Tests on the network geometry reveal best resolution when the seismometers triangulate the source. We conclude that this method can improve the monitoring of rockfall activity in real time once a simulated database for the region of interest is created.

The eastern margin of Madagascar has a prominent relief change from the flat coastal plain to the low-relief high plateau, characterizing a typical great escarpment topography at a passive margin. A quantification of the spatial distribution of erosion rates is necessary to understand the rate of landscape evolution. We present catchment-averaged erosion rates from detrital cosmogenic 10Be concentrations, systematically covering distinct morphological zones of the escarpment. Erosion rates are differentiated across the escarpment, where the high plateau and the coastal plain are slowly eroding with an average rate of 9.7 m/Ma, and the escarpment basins are eroding faster with an average rate of 16.6 m/Ma. The Alaotra-Ankay Graben related basins have the highest erosion rate with an average rate of 27 m/Ma. The spatial pattern of erosion rates indicates a retreating escarpment landscape. Retreat rates calculated from the 10Be concentrations are from 182 m/Ma to 1886 m/Ma. The rates of escarpment retreat on Madagascar are consistent with a model of a steady retreat from the coastline since the time of rifting, similar to the Western Ghats escarpment on its conjugate margin of the India Peninsula.