Following the 2011 M9 Tohoku-Oki earthquake, the interplate seismicity drastically increased in the downdip extension; however, it disappeared within the rupture area. An Mw7.0 earthquake occurred in the downdip extension off Miyagi in March 2021, followed by an Mw6.7 earthquake in May 2021. To examine the initial evolution of the next M9 earthquake cycle, we examined the regional seismicity and source processes of the two M~7 earthquakes. We found that the March Mw7.0 earthquake was nucleated at a conditionally stable patch where repeating earthquakes emerged after the Tohoku-Oki earthquake. The earthquake initiation from a conditionally stable patch at the deep plate boundary is probably a transient feature in the postseismic period of the previous M9 earthquake. The stress enhancement caused by the Mw7.0 event facilitated the subsequent May Mw6.7 earthquake. These two M~7 earthquakes ruptured the western seismic patches of the 1978 Mw7.5 Miyagi-Oki earthquake, which is the most recent typical earthquake in an ~40-year interval of M~7.5 earthquake sequence, and loaded the eastern shallow seismic patches for the sequence. Interplate seismicity in the updip area disappeared after the 2011 Tohoku-Oki earthquake. Assuming that the spatial pattern of interplate earthquakes will be restored to a situation similar to that before the Tohoku-Oki earthquake, the seismically active area should gradually expand to the updip area. Continued monitoring of interplate seismicity is essential to examine how plate-locking evolves during the M9 earthquake cycle.

The north-south seismic zone (NSSZ) is a destructive zone of large-scale earthquakes in China, and the earthquake mechanism associated with deep structures remains unclear. Previous studies have indicated that lithospheric delamination or absence of lithospheres in the western part of the NSSZ may facilitate the eastern extrusion of the Tibetan Plateau and lead to stress accumulation and release. However, the deep process of lithospheric delamination needs to be further clarified. In this study, I collect abundant high-quality teleseismic data recorded by permanent seismic stations and perform common conversion point (CCP) stacking of receiver functions in the north part of the NSSZ. The results show that lithospheric delamination might result in the splitting 660 km discontinuity and a thickening region of the mantle transition zone (MTZ).

Fracturing and gouge formation absorb ≥50% of earthquake energy on low displacement (<1-2 km) faults in isotropic crust. To assess how these processes absorb earthquake energy in anisotropic crust, we performed field and microstructural investigations on the 110 km long, 0.4-1.2 km displacement, Bilila-Mtakataka Fault (BMF), Malawi. Where the fault is parallel to surface metamorphic fabrics, macroscale fractures define a 5-20 m wide damage zone. This is narrow relative to where the BMF is foliation-oblique (20-80 m), and to faults with comparable displacement in isotropic crust (~40-120 m). There is minimal evidence for cataclasis and microfracturing along the BMF; therefore, despite its 110 km length and geomorphic evidence for MW 7-8 earthquakes, widespread fault zone fracturing has not occurred. We attribute lack of damage to fault growth along shallow and deep-seated pre-existing weaknesses. This conclusion implies that earthquake energy dissipates differently along incipient faults in isotropic and anisotropic crust.

To improve the understanding of spatial heterogeneity in fine-grained shale, methods of microscale X-ray fluorescence (μ-XRF) mapping, (ultra-) small-angle x-ray scattering [(U)SAXS] and wide-angle X-ray scattering were used to determine elemental and pore structure variations in sizes up to ~10 cm on two samples prepared at circular (8 cm×8 cm×0.8 mm in width×length×thickness) and rectangular (5 cm×8 cm×0.8 mm) orientations from a piece of Eagle Ford Shale outcrop in South Texas. Thin section petrography and field emission-scanning electron microscopy, X-ray diffraction (XRD), total organic carbon, and pyrolysis were also utilized to investigate the potential spatial heterogeneity of pore types, mineral and organic matter compositions for both samples. Overall, the siliceous-carbonate mineral contents in these carbonate-rich Eagle Ford Shale vary between laminations at mm scales. For the circular sample, porosity and surface area variations range from 0.82 to 3.04% and 1.51 to 14.1 m2/g, respectively. For the rectangular sample, values for porosity and surface area vary from 0.93 to 2.50% and 3.95 to 10.8 m2/g. By analyzing six selected sub-samples on each of two samples with X-ray scattering and XRD techniques, nm-sized pores are mainly interparticle ones in the higher calcite regions, where the porosity is also relatively lower, while the lower calcite regions consist of both interparticle and intraparticle pore types with higher porosity. Finally, the μ-XRF and (U)SAXS are combined to generate porosity distribution maps to provide more insights about its heterogeneity related to the laminations and fractures at our observational scales.

To fully understand the constitutive parameters and the associated mechanism in the velocity-weakening behavior of pyroxene observed in a previous study (He et al., 2013), we employed pure augite (clinopyroxene) as simulated gouge sample to run velocity stepping sliding tests under hydrothermal conditions with temperatures of 101-607 °C, effective normal stress of 200 MPa with 30 MPa pore pressure and axial loading rates of 0.1-1.0 μm/s. From our experiments, we found that: (1) Velocity-strengthening behavior was observed at temperatures of 101-203 °C, the steady-state velocity dependence transitioned to velocity weakening at ~215 °C, and the velocity weakening persisted up to 607 °C, the highest temperature in our experiments. The absolute (b-a) values were revealed to range from 0.0009 to 0.0014, and the inferred average b/a values ranged from 1.15-1.18, both indicating quite weak velocity weakening at temperatures of 303-607 °C. (2) Inferred constitutive parameters through numerical fitting to rate and state friction laws show that the healing effect of friction (b value) has an increasing trend with temperature increase up to 403 °C, indicating an Arrhenius-type thermally-activated creep mechanism behind the healing effect. (3) In addition to microstructural observation of deformed samples that shows remarkable size reduction (crushed grains reduced to scales typically below 1-2 μm) in both intensely sheared regions and moderately sheared regions, ubiquitous precipitated particles (50-100 nm) with platy morphologies were observed to attach to the surfaces of crushed grains, which are typical signatures of intergranular pressure solution process, suggesting that pressure solution was commonly activated at intergranular contacts. (4) No recognizable crystalline plasticity was observed. Our microstructural observation together with the comparison of experimental data with model’s prediction, implies that intergranular pressure solution process at the frictional contacts may be the most likely mechanism operating at the frictional contacts and governing the healing effect for augite.

We propose a reformulation of the wing crack model of brittle creep and brittle failure. Experimental studies suggest that the mechanical interactions of sliding and tensile wing cracks are complex, involving formation, growth and coalescence of multiple tensile, shear and mixed-mode cracks. Inspired by studies of failure in granular media, we propose that these complex mechanical interactions lead to the formation of micro shear-bands, which, in turn, develop longer wing cracks and interact with a wider volume of rock to produce larger shear bands. This process is assumed to indefinitely continue at greater scales. We assume the original wing crack formalism is applicable to micro shear-band formation, with the difference that the half-length, a, of the characteristic micro shear band is allowed to increase with deformation (i.e. wing crack growth). In this approach, the dimensionless shear band half-length A is related to the dimensionless wing crack length L by a function, A(L) = 1 + f(L), where f(L) embodies the entire process of shear band formation, growth and interaction with other shear bands and flaws and the problem is then to identify its proper form. We compare the model predictions for various classes of functions f(L) to experimental brittle creep data. Although a very large class of functions reproduce the classic sequence of tri-modal creep, we found that only the simple power law f(L) = (L/Λ)q generated creep curves consistent with published creep data of rocks. Similar accord was also obtained with experimental brittle failure data.

Although some plasma waves exhibit the largest growth rate and amplitude at 90deg wave normal angle (WNA), particle scattering by these waves in a quasilinear (QL) sense has not been examined previously. Using test-particle calculation and QL theory, the present study investigates the proton scattering by equatorial fast magnetosonic waves (MSWs; a.k.a equatorial noise) with varying WNAs including 90deg. Comparison with the diffusion coefficients in momentum space obtained from the test-particle approach indicates that the QL diffusion coefficients given by, e.g., Kennel and Engelmann (1966) are valid up to 90deg WNA, provided that MSWs described conform to the usual QL theory assumptions. The test-particle dynamics due to MSWs at 90deg WNA are examined in detail. Although in the QL picture, protons are only supposed to resonate with MSWs of integer harmonic frequencies at perpendicular propagation, the presence of slightly off-integer harmonic modes as part of a narrowband discrete spectrum of incoherent MSWs plays an important role in making the proton scattering stochastic. Considering the recent test-particle result of bounce-averaged resonance of energetic protons, non-zero wave power at the WNAs >~ 89.5deg typically excluded in QL diffusion can be important for ring current proton dynamics.

Assessing volcanic hazard in regions of distributed volcanism is challenging because of the uncertain location of future vents. A statistical-mechanical strategy to forecast future vent locations was recently proposed. Here we further develop and test that strategy with analog models. We stress a gelatin block in controlled conditions and observe air-filled crack trajectories. We use the observed surface arrivals to sample the distributions of parameters describing the stress state of the gelatin block, combining deterministic crack trajectory simulations with a Monte Carlo approach. We find the algorithm retrieves the stress imposed on the gelatin and successfully forecasts the arrival points of subsequent cracks in the same experimental setups. We discuss how the approach may be used to gain insight on the stress state of regions of distributed volcanism.

Typical seismic waveform datasets comprise from hundreds of thousands to several millions records. Compilation is performed by time-consuming handpicking of phase arrival times, or signal processing algorithms such as cross-correlation. The latter generally underperform compared to handpicking. However, inconsistencies across and within handpicked datasets creates disagreement between observations and interpretation of Earth’s structure. Here, we exploit the pattern recognition capabilities of Convolutional Neural Networks (CNN). Using a large global handpicked dataset, we train a CNN model to identify the seismic shear phase SS. This accelerates, automates, and makes consistent data compilation. The CNN model is then employed to identify precursors to SS generated by mantle discontinuities. The model identifies precursors in stacked and individual seismograms, producing new measurements of the mantle transition zone with quality comparable to handpicked data. The capability to rapidly obtain new, high-quality observations has implications for automation of future seismic tomography inversions and body wave studies.

The size distribution of frazil ice is currently unconstrained in ice shelf cavity modeling. Here we observe the time-dependent behavior of the number and size of frazil ice particles in an Ice Shelf Water plume. A novel acoustic scattering inversion was used to infer frazil ice crystal diameters, assuming a log-normal distribution. Observation sites were on land-fast sea ice approximately 13 and 33 km from the front of the McMurdo Ice Shelf, Antarctica. The water column from the ice-water interface to 30 m below mean sea level was monitored over 3 weeks in November of 2016 and 2017. At 15 m below sea level the mean frazil crystal diameter was $\sim$\SI{1}{\milli\metre}. Fractional ice volume, derived from frazil crystal size and number density, correlates with in-situ supercooling (up to \SI{50}{\milli\kelvin} at \SI{15}{\metre} below sea level). The data presented here provide valuable input for model initiation and evaluation.

Invasion of solar wind particles inside earth’s magnetosphere induces the distortion of geomagnetic setting of earth. This geomagnetic disturbances be a consequence of energy discharge of solar plasma in different forms such as visible aurora in the polar region, joule heating, ring current energy; momentary fluctuation of earth’s magnetic field (SYM-H), intensification of magnetospheric current system; Field Aligned Current (FAC) and Polar Cap Potential (PCV) and many other phenomena. However, this event can cause some serious calamites, so having better understanding of it and able to be prepared in any severity of such situations is always in good accord. For this, we studied total of nine different intense geomagnetic storms from solar cycle 22, 23 and 24. Events included from solar cycle 22 and 24 were triggered by Stream Interaction Region (SIR) as well as SIR associated with complex structures which were a resultant of interactions between SIRs and Interplanetary Coronal Mass Ejections (ICMEs) respectively. The rest of the selected events which are all from solar cycle 23 were also the responses of solar structures like SIR and ICME along with sheath and magnetic cloud. To understand the impact of the solar wind particles on near earth space, magnetospheric and interplanetary parameters such as IMF-Bz, SYM-H, PCV and FAC are graphed along with total solar input energy and other energy sinks like auroral precipitation, joule heating, and ring current energy. To substantiate result, cross‐correlation technique is used along with pie chart and bar graphing which has helped in statistical investigation.

In case of earthquakes and crustal movement, the concentration of impounding load over a large region of crust can cause disturbances to the stratum. In order to quantitatively investigate crack initiation, propagation and coalescence processes of jointed stratum based on thermal variations caused by concentrated mechanical loading, a series of indention tests were performed on granite specimens. In the experiment, fracture process and resulting infrared radiation fields of specimens were respectively recorded by synchronized digital image correlation system and infrared camera. Then, thermal characteristics of mixed shear-tensile and tensile conical crack were analyzed. Experimental results indicate that the highlighted temperature localization is mainly caused by shear deformation within the localized fracture process zone. It is shown that in the initiation process, the abnormities in the temperature concentration factors are caused by the frictional-thermal effect for mixed mode crack and the thermoelastic effect for tensile mode crack. Subsequently, in the propagation process, these two crack types followed newly proposed criteria, namely, the maximum temperature gradient criterion for mixed mode crack and the minimum temperature gradient criterion for tensile mode crack. In addition, the intensity of temperature concentrations in crack initiation stage and coalescence stage are more pronounced than that of crack propagation stage. These thermal effects strongly correlated with the stress states in the cracking process. The new findings from the infrared radiation temperature distributions improve our understanding of fracturing process of rock mass. Furthermore, it will provide some fundamental references for geophysical prospecting in jointed rock mass.

In response to frequent fatal beach drownings, China’s first operational attempt on the rip current hazard investigation was made by the National Marine Hazard Mitigation Service (NMHMS). A great number of recreational beaches were found developing rip currents interlaced with rhythmic sandbars, varying by season and location evidenced by satellite images and morphodynamic calculation. Considering insufficient understanding of the multi-channel rip system, case analysis and numerical study were conducted to explore its dynamicity and circulation characteristics under various wave climates in present work. The strength of rip currents was generally proportional to wave height and channel width under certain limits. Increasing wave height was not always a promotion and could even weaken the rip current due to the strong wave-current shear. Interesting “pump” and “feed” interactions between adjacent rip currents in the multi-channel system were observed. The rip current might be totally absent in narrow channels when the majority of water flows through neighboring broader pathways. The rip current was highly sensitive to the incident wave angle. Alongshore currents prevailed over the rip current when the wave angle reached 11 degrees to shore normal, which was not favorable to the existence of channeled sandbars. Vortices appeared around the edge of the bar owing to nonuniform wave breaking over rapid-varying bathymetry. The setup water was created shoreward by the sandbar array and substantially increased as the wave deviated from the normal incidence. The water surface depression in the rip channel was not observed as the wave angle increased, which fundamentally explained why the rip current could not persist when the incident wave became slightly oblique. In future, incident wave angle should be further incorporated into empirical formulas or probabilistic models to predict the rip current for expected improvement in accuracy.

Wheat production plays an important role in Morocco with the country typically producing more than half of Northwest African grain production. Current wheat forecast systems use weather and vegetation data during the crop growing phase, thus limiting the earliest possible release date to early spring. However, Morocco's wheat production is mostly rainfed and thus strongly tied to fluctuations in rainfall, which in turn depend on slowly evolving climate dynamics. This offers a source of predictability at longer timescales. Using physically-guided causal discovery algorithms we extract climate precursors for wheat yield variabilityfrom gridded fields of geopotential height and sea surface temperatures which show potential for accurate yield forecasts already in December. The detected interactions are physically meaningful and consistent with documented ocean-atmosphere feedbacks. Reliable yield forecasts at such long lead times could provide farmers and policy-makers with necessary information for early action and strategic adaptation measurements to support food security.

The equivalent source method of Spherical Elementary Current Systems (SECS) has contributed valuable results for spatial magnetic interpolation purposes where no observations are available, as well as for modeling equivalent currents both in the ionosphere and in the subsurface, thus providing a separation between external and internal sources. It has been successfully applied to numerous Space Weather (SW) events, whereas some advantages have been reported over other techniques such as Fourier or Spherical (Cap) Harmonic Analysis. Although different modalities of SECS exist (either 1-D, 2-D or 3-D) depending on the number of space dimensions involved, the method provides a sequence of instantaneous pictures of the source current. We present an extension of SECS consisting in the introduction of a temporal dependence in the formulation based on a cubic B-splines expansion. The technique thus adds one dimension, becoming 4-D in general (e.g., 3D + t), and its application is envisaged for, though not restricted to, the analysis of past events including heterogeneous geomagnetic datasets, such as those containing gaps, different sampling rates or diverse data sources. A synthetic model based on the Space Weather Modeling Framework (SWMF) is used to show the efficacy of the extended scheme. We apply this method to characterize the current systems of past and significant SW events producing geomagnetically induced currents (GIC), which we exemplify with an outstanding geomagnetic sudden commencement (SC) occurred on March 24, 1991.

We use fast synchrotron X-ray imaging to understand three-phase flow in mixed-wet porous media to design either enhanced permeability or capillary trapping. The dynamics of these phenomena are of key importance in subsurface hydrology, carbon dioxide storage, oil recovery, food and drug manufacturing, and chemical reactors. We study the dynamics of a water-gas-water injection sequence in a mixed-wet carbonate rock. During the initial waterflooding, water displaced oil from pores of all size, indicating a mixed-wet system with local contact angles both above and below 90 •. When gas was injected, gas displaced oil preferentially with negligible displacement of water. This behaviour is explained in terms of the gas pressure needed for invasion. Overall, gas behaved as the most non-wetting phase with oil the most wetting phase; however pores of all size were occupied by oil, water and gas, as a signature of mixed-wet media. Thick oil wetting layers were observed, which increased oil connectivity and facilitated its flow during gas injection. A chase waterflooding resulted in additional oil flow, while gas was trapped by oil and water. Furthermore, we quantified the evolution of the surface areas and both Gaussian and the total curvature, from which capillary pressure could be estimated. These quantities are related to the Minkowski functionals which quantify the degree of connectivity and trapping. The combination of water and gas injection, under mixed-wet immiscible conditions leads to both favourable oil flow, but also to significant trapping of gas, which is advantageous for storage applications.

The Vavilov Ice Cap destabilized in 2013. It reached its highest annual ice loss rate of 4.48 km3/yr between 2015 and 2016, a rate that is more than half of the entire combined ice loss from all the other ice caps in the Russian Arctic. To understand the mechanics of how the surge took place and what will happen in the future, we investigate surface elevation and glacier velocities using the Cryosphere And Remote Sensing Toolkit (CARST), an open-access python toolbox designed for processing temporal changes of high-resolution remote sensing data. We use optical satellite images from WorldView, Landsat, and Sentinel-2 and their derived elevation and velocity products to track the history of the surge between 2010 and the present. We propose that the surge initiated when the ice front overrode weak marine sediments in 2013, leading to a reduction of frontal friction. Velocity time series show that the glacier reached a maximum speed of 25 m/day (9 km/yr) in late 2015, when a piedmont-like ice lobe stretched more than 10 km into the Kara Sea. However, in spring 2017 the glacier slowed down to 7-9 m/day with the development of a new channel inside the piedmont lobe, with new shear margins visible from optical imagery. The channelized flow pushes through the grounded portion of the piedmont glacier, and suggests a further reorganization of resistive forces. The unprecedented evolution of the surge at Vavilov Ice Cap shows a strong connection to the status of the terminus, which might pose general concern for the stability of marine- or lake-terminating glaciers regardless of their locations on Earth.

The Chilean subduction zone is one of the most seismically active regions on Earth, due to the shallow depth of the seismogenic zone in combination with the high coupling coefficients and high plate convergence rate. On February 27, 2010, the Maule earthquake, which is one of the strongest instrumentally registered megathrust earthquakes, occurred in Darwin seismic gap – a seismically calm zone existed near the coast of Chile since 1835. We use the keyboard model of generation of strong subduction earthquakes [Lobkovky et al., 1991] to analyze the peculiarities of seismic deformation cycle (SDC) related to the Darwin seismic gap and the 2010 earthquake. Keyboard structure of the South American continental margin near the source zone of the Maule earthquake is confirmed by seismological and geological data. Using of keyboard model allows us to associate interseismic, coseismic and postseismic deformations observed by satellite geodesy with the action of particular geodynamic processes and, therefore, to study their features. To achieve this aim, we analyze the data of almost 10 years of continuous observations at 76 stations of the Chilean GPS network deployed along the source zone of the 2010 Maule earthquake. The analysis of variations in surface deformation fields is based on displacement rates fields of GPS stations estimated over 1-year intervals. On the basis of registered coseismic displacements we construct a model of slip distribution in the source zone of the Maule earthquake and determine the magnitudes of instantaneous shifts of seismogenic blocks towards the ocean, which reached 1-3 meters. In the first two years after the 2010 earthquake GPS stations shift toward the ocean over the whole Central Chile region, which indicates passing of aftershock stage of the SDC. Over the next 7 years of observations, the observed displacements can be mainly explained by the process of restoring the stationary state of stress accumulation for seismogenic blocks in the frontal part of the subduction zone in combination with the continuing displacement of the rear massif by a viscous asthenospheric flow. To assess the time of transition of seismogenic zone to stationary state of accumulation of elastic stresses we construct models of frictional afterslip and viscoelastic relaxation in the asthenosphere. The durations of the afterslip and viscoelastic relaxation processes for the Maule earthquake are according to our estimates about half a year and more than 15 years respectively. Understanding of the features of the SDC plays a significant role in the seismic hazard assessment of the Maule and Biobio regions of Chile.

The InSight mission [1] landed in November 2018 in the Elysium Planitia region [2] bringing the first geophysical observatory to Mars. Since February 2019 the seismometer SEIS [3] has continuously recorded Mars’ seismic activity, and a list of the seismic events is available in the InSight Marsquake Service catalog [4]. In this study, we predict present-day seismic velocities in the Martian interior using the 3D thermal evolution models of [5]. We then use the 3D velocity distributions to interpret seismic observations recorded by InSight. Our analysis is focused on the two high quality events S0173a and S0235b. Both have distinguishable P- and S-wave arrivals and are thought to originate in Cerberus Fossae [6], a potentially active fault system [7]. Our results show that models with a crust containing more than half of the total amount of heat producing elements (HPE) of the bulk of Mars lead to large variations of the seismic velocities in the lithosphere. A seismic velocity pattern similar to the crustal thickness structure is observed at depths larger than 400 km for cases with cold and thick lithospheres. Models, with less than 20% of the total HPE in the crust have thinner lithospheres with shallower but more prominent low velocity zones. The latter, lead to shadow zones that are incompatible with the observed P- and S-wave arrivals of seismic events occurring in Cerberus Fossae, in 20° - 40° epicentral distance. We therefore expect that future high-quality seismic events have the potential to further constrain the amount of HPE in the Martian crust. Future work will combine the seismic velocities distribution calculated in this study with modeling of seismic wave propagation [8, 9]. This will help to assess the effects of a 3D thermal structure on the waveforms and provide a powerful framework for the interpretation of InSight’s seismic data. [1] Banerdt et al., Nat. Geo. 2020; [2] Golombek et al., Nat. Comm. 2020, [3] Lognnoné et al., Nat. Geo. 2020, [4] InSight MQS, Mars Seismic Catalogue, InSight Mission V3, 2020, https://doi.org/10.12686/A8, [5] Plesa et al., GRL 2018, [6] Giardini et al., Nat. Geo. 2020, [7] Taylor et al., JGR 2013, [8] Bozdag et al., SSR 2017, [9] Komatitsch & Tromp, GJI 2002.

Submarine slope failures and the tsunamis they generate pose risks to coastal communities and infrastructure. While slope failures on passive margins represent some of the largest mass failures on Earth, little is known about their dynamics. The recurrence interval of submarine slope failures on passive margins is longer than on active margins, which facilitates thick sediment accumulation before failure, yields larger failures, and may be associated with higher potential for tsunami generation. While numerous studies model failure likelihood based on temporal distribution, overpressure, or earthquake proximity, there is limited insight linking initial conditions, preconditioning, slope failure initiation, and failure evolution. We observed dynamic submarine slope failure processes via physical experiments in a benchtop flume. Submarine slope failures were induced under controlled pore pressure with varied sand-clay mixtures (0%, 2%, 4%, and 5%, clay, by weight) constrained to a constant pre-failure slope geometry. Commercially obtained fine-grained sand (subangular quartz; 87% SiO2; D50 = 195 µm) and clay (dioctahedral smectite; 63% SiO2 and 21% Al2O3; D90 = 44 µm) were used. Pore pressure required to induce slope failure, slope-failure initiation and evolution, and post-failure morphology were recorded and analysed via photogrammetry. Numerical models were developed to quantify the physical processes observed in flume experiments. Increased clay content corresponded to increased cohesion and pore pressure required for failure. Subsurface fractures and tensile cracks were only generated in experiments containing clay. Falling head tests showed a log-linear relation between hydraulic conductivity and clay content which we used in our numerical models. Models of our experiments effectively simulate overpressure (pressure in excess of hydrostatic) and failure potential for (non)cohesive sediment mixtures. Overall our work shows the importance of clay in reducing permeability and increasing cohesion to create different failure modes due to overpressure. Ongoing work is investigating the effects of higher clay content and the role of seismic energy in slope failure morphology.

Representing climate-crop interactions is critical to earth system modeling. Despite recent progress in modeling dynamic crop growth and irrigation in land surface models (LSMs), transitioning these models from field to regional scales is still challenging. This study applies the Noah-MP LSM with dynamic crop-growth and irrigation schemes to jointly simulate the crop yield and irrigation amount for corn and soybean in the central U.S. The model performance of crop yield and irrigation amount are evaluated at county-level against the USDA reports and USGS water withdrawal data, respectively. The bulk simulation (with uniform planting/harvesting management and no irrigation) produces significant biases in crop yield estimates for all planting regions, with root-mean-square-errors (RMSEs) being 28.1% and 28.4% for corn and soybean, respectively. Without an irrigation scheme, the crop yields in the irrigated regions are reduced due to water stress with RMSEs of 48.7% and 20.5%. Applying a dynamic irrigation scheme effectively improves crop yields in irrigated regions and reduces RMSEs to 22.3% and 16.8%. In rainfed regions, the model overestimates crop yields. Applying spatially-varied planting and harvesting dates at state-level reduces crop yields and irrigation amount for both crops, especially in northern states. A “nitrogen-stressed” simulation is conducted and found that the improvement of irrigation on crop yields are limited when the crops are under nitrogen stress. Several uncertainties in modeling crop growth are identified, including yield-gap, planting date, rubisco capacity, and discrepancies between available datasets, pointing to future efforts to incorporating spatially-varying crop parameters to better constrain crop growing seasons.

Terrestrial space weather involves the transfer of energy and momentum from the solar wind into geospace. Despite recently discovered seasonal asymmetries between auroral forms and the intensity of emissions between northern and southern hemispheres, seasonally averaged energy input into the ionosphere is still generally considered to be symmetric. Here we use Swarm satellite data to show an unexpected preference for electromagnetic energy input at 450 km altitude into the northern hemisphere, on both the dayside and the nightside, when averaged over season. We propose that this is explained by the offset of the magnetic dipole away from Earth’s center. This introduces a larger separation between the magnetic pole and rotation axis in the south, creating different relative solar illumination of northern and southern auroral zones, resulting in changes to the strength of reflection of incident Alfvén waves from the ionosphere. Our study reveals an important asymmetry in seasonally averaged electromagnetic energy input to the atmosphere. Based on observed lower Poynting flux on the nightside this asymmetry may also exist for auroral emissions. Similar offsets may drive asymmetric energy input, and potentially aurora, on other planets.

New shipborne surveys provide a closely spaced magnetic anomaly dataset covering the East Subbasin (ESB) of the South China Sea (SCS). Magnetic anomalies of seafloor spreading are identified using the dataset supplemented with previous data and age constraints from recent International Ocean Discovery Program Expeditions 349 and 367/368 holes. We present a high-resolution oceanic crustal age model and associated magnetic lineations of the ESB based on identified magnetic anomaly picks. Seafloor spreading in the ESB initiated at ~30 Ma (C11n) and terminated at ~16 Ma (C5Br). The spreading direction has experienced a gradual counterclockwise rotation between C6Cr and C5Er and a significant counterclockwise rotation at C5Dr. The spreading rotations reorganized the orientation and segmentation of the spreading ridge, resulting in the formation of a series of S-shaped fracture zones. The interpretation of the magnetic lineations reveals that three southward ridge jumps occurred at C9r, C8n, and C7n and a synchronous jump occurred at C5Dr. Three southward ridge jumps contributed to a total difference of ~184 km in the distance between the two flanks and left the paired magnetic lineations C10r–C7r on the present-day north flank. The synchronous jump caused the spreading ridge to rotate rapidly counterclockwise and obliquely intersect the existing seafloor. We postulate that these ridge jumps and rotations are common processes during seafloor spreading reorientation and are dynamic responses to the plate or microplate tectonics around the SCS.

This paper presents the results of modeling the lower ionosphere response to solar X-ray flares of C-, M- and X-classes. The model is based on a 5-component scheme of the ionization-recombination cycle of the ionospheric D-region. Input parameters of the plasma-chemical model under different heliogeophysical conditions corresponding to selected X-ray flares were determined by using data received from AURA, SDO and GOES satellites. Verification of the obtained results was carried out with use of ground-based radiophysical measurements taken at the geophysical observatory Mikhnevo. Results of comparing the calculated and experimental the radio wave amplitude variations along six European very low frequency (VLF) paths show that the root mean square error (RMSE) does not exceed 1.5 dB for ~70% of cases including X-class flares during which the amplitude jump on some paths reaches 8 dB. Qualitative and quantitative analysis of the verification results of the VLF signal amplitude has showed the good predictive capability of the built model for describing weak and moderate ionospheric disturbances.