Southeastern Tibet is a key region for studying the tectonic evolution of Tibetan Plateau. The region is characterized by distributed faults, localized low-velocity zones (LVZs) in the mid-lower crust, and prominent clockwise rotation of GPS velocity field. End-member models have been proposed to explain the origin of this deformation pattern, including the block extrusion model highlighting the role of faulted shear zones, and the crustal flow model emphasizing the effect of a weak lower crust. Here we use a 3D visco-elasto-plastic finite element model to reproduce the instantaneous horizontal surface velocity and investigate the effects of active faults and LVZs on that. The results show that when only faults are included, the residual surface velocities between modeled and observed values are large at some locations overlying the LVZs; when only LVZs are included, the residual surface velocities along the Xianshuihe-Xiaojiang and Lijiang-Xiaojinhe faults, two major faults with relatively high slip rates, are significant. However, when both faults and LVZs are considered, the modeled surface velocities fit well with observed GPS velocities. Our results therefore demonstrate that a combination of fault-bounding block extrusion and crustal flow type of continuous deformation is required to explain the surface deformation. The model yields a high-resolution strain rate map which provides an improved understanding of Quaternary tectonics and seismic hazards. In order to reduce the residual velocities, the viscosity of LVZs is constrained as ~10-10 Pa·s. Our study also suggests that LVZs are probably partially molten, which explains the rheology, seismological, and magnetotelluric data.

We explore two possible Earth climate scenarios, 200 and 250 million years into the future, using projections of the evolution of plate tectonics, solar luminosity, and rotation rate. In one scenario, a supercontinent forms at low latitudes, whereas in the other it forms at high \change{northerly}{northern} latitudes with an Antarctic subcontinent remaining at the south pole. The climates between these two end points are quite stark, with differences in mean surface temperatures approaching several degrees. The main factor in these differences is related to the topographic height of the high latitude supercontinents where higher elevations promote snowfall and subsequent higher planetary albedos. These results demonstrate the need to consider \change{alternative}{multiple} boundary conditions when simulating Earth-like exoplanetary climates.

In order to investigate seismic structures beneath the Australian continent and slab geometry of subduction zones around the Australian plate, we construct a new radially anisotropic shear wavespeed model, namely AU21, by applying full-waveform inversion technique to three-component data from 248 regional earthquakes and recorded by 1,102 seismographic stations. Twenty one preconditioned conjugate gradient iterations are utilized to minimize discrepancies between observed and synthetic seismograms, resulting 32,655 body-wave (15-40 s) and 35,897 surface-wave (25-100 s) measurements in the final iteration. AU21 confirms the sharp contrast in shear wavespeed perturbations between the Phanerozoic eastern continental margin with the Precambrian western and central Australia, and this boundary is offset to the east of the Tasman Line. The lithosphere-asthenosphere boundary is about 250-300 km beneath central and western Australia. A unique weak radial anisotropy layer at 80-150 km is observed beneath the western Australian craton, which may be caused by dipping layers alignments or tilted symmetry axes of anisotropic minerals. Slow anomalies extending down to the uppermost lower mantle beneath east of New Guinea, the Tasman Island, and the Tasman Sea may suggest deep thermal activities beneath these regions, possibly contributing to the formation of the low wavespeed band along the eastern Australian margin. Furthermore, we observe that the Tonga slab is stagnant within the mantle transition zone, while the Kermadec slab penetrates through the 660-km discontinuity down to the lower mantle.

We employ Magnetospheric Multiscale, Geostationary Operational Environmental and Los Alamos National Laboratory satellites, as well as the ground magnetometer networks over Greenland and North America to study a substorm on 9 August 2016 between 9 and 10 UT.We found that during the substorm two earthward flows, whose dipolarization-injection fronts exceeded 6.5 and 4 Earth’s radii (RE) in YGSM, impinged and rebounded from Earth’s dipolar field lines at L = 6–7 downtail, where L is the McIlwain number. The impingements and rebounds ended with a substorm current system of downward R1 and upward R2 currents which grew to azimuthally cover the whole North American continent. At the fronts, regions of enhanced negative j·E′ were formed and peaked toward the end of the impingements. These regions appeared to be conjugate with eastward moving aurora (along the growth phase arc and together with eastward drifting energetic electrons at geosynchronous equatorial orbit), which manifests ionospheric Ohmic losses.

The COVID-19 virus was first detected in Wuhan, China and its genesis was traced to infected bats, passed through an intermediate host to humans. COVID-19 or “Coronavirus” reached approximately 4 million confirmed cases in the United States by July 2020. The spread of this virus has affected both social and economic affairs on a global scale with more than 15 million confirmed cases worldwide in July 2020. The pandemic has proven a global public health and socio-economic crisis. In addition, the shelter-in-place orders provide an unprecedented opportunity for examining the resulting reduction in greenhouse gases and aerosols on the atmosphere. The Sentinel-5P satellite has shown distinct changes in atmospheric aerosols over the COVID-19 epicenter in Wuhan. After Texas, U.S. established similar shelter-in-place orders to prevent the spread of the virus, the state’s industrial activity experienced an economic slowdown. This paper quantifies the changes in atmospheric aerosols associated with the COVID-19 slowdown over major cities in Texas and compares it to similar changes in Wuhan, China using satellite imagery.

2-D finite element modeling of both coseismic and interseismic deformation was performed along a transect across the seismogenic fault of the Mw=7.3, November 2017 Lurestan earthquake (Zagros Mountains). In order to extract information on the time-space distribution of uplift along the same transect, an investigation of the large-scale features of topography and river network was also carried out. Constraints from the spatial distribution of mean elevation, local relief and normalized channel steepness index (ksn), combined with those from river longitudinal profiles and transformed river profiles (chi-plots), were integrated with the results of geomorphological analyses aimed at the reconstruction of the development of the fluvial network. Despite the much longer timescale over which topography grows and/or rivers respond to tectonic or climatic perturbations with respect to even multiple seismic cycles, the outputs of the finite element model yield fundamental information on the source of the late part of the spatiotemporal evolution of surface uplift recorded by the geomorphological signature. Model outputs shed new light into the processes controlling relief evolution in an actively growing mountain belt underlain by a major blind thrust. They point out how co-seismic slip controls localized uplift of a prominent topographic feature ­– defining the Mountain Front Flexure – located above the main upper crustal ramp of the principal basement thrust fault of the region, while continuous displacement along the deeper, aseismic portion of the same basement fault controls generalized uplift of the whole crustal block located further to the NE, in the interior of the orogen.

The Wyoming Craton underwent tectonic modifications during the Laramide Orogeny, which resulted in a series of basement-cored uplifts that built the modern-day Rockies. The easternmost surface expression of this orogeny - the Black Hills in South Dakota - is separated from the main trend of the Rocky Mountains by the southern half of the Powder River Basin, which we refer to as the Thunder Basin. Seismic tomography studies reveal a high-velocity anomaly which extends to a depth of ~300 km below the basin and may represent a lithospheric keel. We constrain seismic attenuation to investigate the hypothesis that the variations in lithospheric thickness resulted in the localization of stress and therefore deformation. We utilize data from the CIELO seismic array, a linear array that extends from east of the Black Hills across the Thunder Basin and westward into the Owl Creek Mountains, the BASE FlexArray deployment centered on the Bighorn Mountains, and the EarthScope Transportable Array. We analyze seismograms from deep teleseismic events and compare waveforms in the time-domain to characterize lateral varations in attenuation. Bayesian inversion results reveal high attenuation in the Black Hills and Bighorn Mountains and low attenuation in the Thunder and Bighorn basins. Scattering is rejected as an confounding factor because of a strong anticorrelation between attenuation and the amplitude of P wave codas. The results support the hypothesis that lateral variations in lithospheric strength, as evidenced by our seismic attenuation measurements, played an important role in the localization of deformation and orogenesis during the Laramide Orogeny.

We present indirect measurements of size-resolved ultrafine particle composition conducted during the Ocean–Atmosphere–Sea Ice–Snowpack (OASIS) Campaign in Utqiagvik, Alaska, during March 2009. This study focuses on measurements of size-resolved particle hygroscopicity and volatility measured over two periods of the campaign. During a period that represents background conditions in this location, particle hygroscopic growth factors (HGF) at 90% relative humidity ranged from 1.45-1.51, which combined with volatility measurements suggest a mixture of ~30% ammoniated sulfates and ~70% oxidized organics. Two separate regional ultrafine particle growth events were also observed during this campaign. Event 1 coincided with elevated levels of H2SO4 and solar radiation. These particles were highly hygroscopic (HGF=2.1 for 35 nm particles), but were almost fully volatilized at 160 °C. The air masses associated with both events originated over the Arctic Ocean. Event 1 was influenced by the upper marine boundary layer, while Event 2 spent more time closer to the surface and over open ocean leads, suggesting marine influence in growth processes. Event 2 particles were slightly less hygroscopic (HGF=1.94 for 35nm and 1.67 for 15nm particles), and similarly volatile. We hypothesize that particles formed during both events contained 60-70% hygroscopic salts by volume, with the balance for Event 1 being sulfates and oxidized organics for Event 2. These observations suggest that primary sea spray may be an important initiator of ultrafine particle formation events in the Arctic late-winter, but a variety of processes may be responsible for condensational growth.

In three consecutive years from 2016 to 2018, extreme ocean warming events, or marine heatwaves (MHW), occurred during boreal summers in the East China Sea (ECS) and South Yellow Sea (SYS), which is unprecedented in the past four decades based on the satellite record. In this study, we used a high-resolution hydrodynamic model based on FVCOM (Finite Volume Community Ocean Model) to simulate the evolution of these warming events. An upper ocean temperature budget (0-20m) analysis based on the model results shows that the shortwave radiation and the ocean advection anomalies jointly contributed to the anomalous warming in the three successive summers (June-August) in the SYS and the north part of the ECS. In addition, the reduction of surface wind speeds during the 2016 and 2017 summers further weakened the vertical mixing, thereby enhancing the anomalous warming in the north part of the ECS adjacent to the SYS. During the three summers, the increases of shortwave radiation were closely related to the East Asian Summer Monsoon (EASM) variability, which reduced the cloud cover in the ECS and SYS, whereas the advection anomalies were mostly associated with regional wind anomalies. In summer 2018, upper ocean heat was transported into the central trough of the South Yellow Sea, accumulated in an anticyclonic eddy generated by the anomalous wind stress curls. Therefore, despite the primary driver of the MHWs is the EASM variation, regional processes are critical to driving the spatial pattern of the MHW intensity in the ECS and SYS.

Turbulent boundary layers are populated by a hierarchy of recurrent structures normally referred to as “coherent structures.” Among others, ejection and sweep events are critical coherent structures of large-scale motions in turbulent flows. This study focused on gaining a better understanding of the spatial-temporal probabilistic characteristics of sweep and ejection events. The existence of uniform momentum zones (UMZs) is demonstrated to affect the spatial distribution of large-scale motions, and the ejection and sweep events tend to present near UMZ edges. On the basis of such observations, we considered the effect of UMZ edges on the presence of ejection and sweep events. In the current study, UMZ detection was employed to identify coherent structures. Several criteria for identifying coherent structures are revisited, and an integrated standard is applied to the available direct numerical simulation (DNS) turbulent channel flow data after UMZ edges were determined. Based on the integrated criterion for distinguishing ejection and sweep events, one can determine the probabilistic characteristics of coherent structures such as the maximum height, wall-normal length and streamwise length. Physical insights from DNS data such as joint probability density functions of wall-normal length and streamwise length can be established. The attached and detached features of the sweep and ejection coherent structures can then be classified and characterized, respectively. Durations of sweep and ejections events were demonstrated to follow a lognormal distribution in this study. The occurrence ratio of sweep events in the large-scale motions (LSMs) was quantified from the DNS data.

After ca. 250 kyr without a known eruption, in recent decades Uturuncu volcano in Bolivia has exhibited multiple signs of unrest, making the classification of this system as “active”, “dormant”, or “extinct” a complex question. Previous work identified anomalous low resistivity zones at <10 km depth with ambiguous interpretations. We investigate subsurface structure at Uturuncu with new gravity data and analysis, and compare these data with existing geophysical data sets. We collected new gravity data on the edifice in November 2018 with 1.5 km spacing, improving the resolution of existing gravity data at Uturuncu. Gradient analysis and geophysical inversion of these and older gravity data revealed a 5 km diameter, positive density anomaly beneath the summit of Uturuncu (1-3 km elevation) and a 20 km diameter arc-shaped negative density anomaly around the volcano (-3 to 4 km elevation). These structures often align with resistivity anomalies previously detected beneath Uturuncu, although the relationship is complex, with the two models highlighting different components of a common structure. Based on a joint analysis of the density and resistivity models, we interpret the positive density anomaly as a zone of sulfide deposition with connected brines, and the negative density arc as a surrounding zone of hydrothermal alteration. Based on this analysis we suggest that the unrest at Uturuncu is unlikely to be pre-eruptive. This study shows the value of joint analysis of multiple types of geophysical data in evaluating volcanic subsurface structure at a waning volcanic center.

Seismic inverse modeling is a common method in reservoir prediction and it plays a vital role in the exploration and development of oil and gas. Conventional seismic inversion method is difficult to combine with complicated and abstract knowledge on geological mode and its uncertainty is difficult to be assessed. The paper proposes an inversion modeling method based on GAN consistent with geology, well logs, seismic data. GAN is a the most promising generation model algorithm that extracts spatial structure and abstract features of training images. The trained GAN can reproduce the models with specific mode. In our test, 1000 models were generated in 1 second. Based on the trained GAN after assessment, the optimal result of models can be calculated through Bayesian inversion frame. Results show that inversion models conform to observation data and have a low uncertainty under the premise of fast generation. This seismic inverse modeling method increases the efficiency and quality of inversion iteration. It is worthy of studying and applying in fusion of seismic data and geological knowledge.

This paper presents a new discretization of the rotating shallow water equations and a set of decisions, ranging from a simplification of the continuous equations down to the implementation level, yielding a code that is fast and accurate. Accuracy is reached by using WENO reconstructions on the mass flux and on the nonlinear Coriolis term. The results show that the build-in mixing and dissipation, provided by the discretization, allow a very good material conservation of potential vorticity and a minimal energy dissipation. Numerical experiments are presented to assess the accuracy, which include a resolution convergence, a sensitivity on the the free-slip vs. no-slip boundary conditions, a study on the separation of waves from vortical motions. Speed is achieved by a series of choices rather than a single recipe. The main choice is to discretize the covariant form written in index coordinates. This form, rooted in the discrete differential geometry, removes most of the grid scale terms from the equations, and keep them only where they should be. The model objects appearing in resulting continuous equations have a natural correspondence with the grid cell features. The other choices are guided by the maximization of the arithmetic intensity. Finally this paper also proves that a pure Python implementation is not only possible but also very fast, thanks to the possibility of having compiled Python. As a result, the code performs 2 TFlop per second using thousand cores.

Large earthquakes are usually modeled with simple planar fault surfaces or a combination of several planar fault segments. However, in general, earthquakes occur on faults that are non-planar and exhibit significant geometrical variations in both the along-strike and down-dip directions at all spatial scales. Mapping of surface fault ruptures and high-resolution geodetic observations are increasingly revealing complex fault geometries near the surface and accurate locations of aftershocks often indicate geometrical complexities at depth. With better geodetic data and observations of fault ruptures, more details of complex fault geometries can be estimated resulting in more realistic fault models of large earthquakes. To address this topic, we here parametrize non-planar fault geometries with a set of polynomial parameters that allow for both along-strike and down-dip variations in the fault geometry. Our methodology uses Bayesian inference to estimate the non-planar fault parameters from geodetic data, yielding an ensemble of plausible models that characterize the uncertainties of the non-planar fault geometry and the fault slip. The method is demonstrated using synthetic tests considering checkerboard fault-slip patterns on non-planar fault surfaces with spatially-variable dip and strike angles both in the down-dip and in the along-strike directions. The results show that fault-slip estimations can be biased when a simple planar fault geometry is assumed in presence of significant non-planar geometrical variations. Our method can help to model earthquake fault sources in a more realistic way and may be extended to include multiple non-planar fault segments or other geometrical fault complexities.

The effect of non-uniform solar radiation over opposing hillslopes leads to aspect-controlled vegetation patterns in semi-arid ecosystems. It creates a differentiation in soil properties and vegetation characteristics. In mid- to high-latitudes where available soil moisture is a limiting factor for vegetation growth, slopes with polewardfacing aspect tend to develop denser vegetation cover that provides more erosion protection than on the equatorward-facing hillslopes. The variation in erosion rates across opposing hillslopes causes the topographic asymmetry of hillslopes over long timescales. The magnitude of this asymmetry is measured by the hillslope asymmetry index (HAI), a metric given as the ratio of the median slope angles of opposite hillslopes. In this study, we present a novel approach to investigate the relationships of HAI with climatological, geomorphic, and ecologic variables at a global scale. Here, we analyzed these relationships using DEM data to compute HAI for 80 different catchments across the world, in which aspect-controlled vegetation has been reported in the literature. We used the CHILD landscape evolution model (LEM), which uses the continuity equation for water, sediment, and biomass, in order to investigate the control of climatological, geomorphic, and ecologic variables on the development of hillslope asymmetry. Preliminary results show that latitude and mean topographic gradient are the two dominant factors affecting hillslope asymmetry due to their vital role in controlling vegetation density through the modulation of incoming solar radiation. These results improve our understanding on how different climatic variables and geographic properties affect the magnitude of hillslope asymmetry and their implications on landform evolution modelling.

Magmatic segregation and volcanic eruptions transport tidal heat from Io’s interior toits surface. Several observed eruptions appear to be extremely high temperature (≥1600 K),suggesting either very high degrees of melting, refractory source regions, or large amountsof viscous heating on ascent. To address this ambiguity, we develop a model that cou-ples crust and mantle dynamics to a simple compositional system. We analyse the modelto investigate chemical structure and evolution. We demonstrate that magmatic segre-gation and volcanic eruptions lead to differentiation of the mantle, the extent of whichdepends on how easily high temperature melts from the more refractory lower mantlecan migrate upwards. We propose that Io’s highest temperature eruptions originate fromthis lower mantle region, and that such eruptions act to limit the degree of compositionaldifferentiation.

The Icelandic crust is a product of its unique tectonic setting, where the interaction of an ascending mantle plume and the mid-Atlantic Ridge has caused elevated mantle melting, which has accreted and cooled in the crust to form an oceanic plateau. Here, we investigate the strength, orientation and distribution of seismic anisotropy in the upper crust of the Northern Volcanic Zone using local earthquake shear wave splitting, with a view to understanding how the contemporary stress field may influence sub-wavelength structure and processes. This is achieved using a dataset comprising >50,000 earthquakes located in the top 10 km of the crust, recorded by up to 70 stations over a 9 year period. We find that anisotropy is largely confined to the top 3–4 km of the crust, with an average delay time of 0.10 ± 0.08 s and an average orientation of the fast axis of anisotropy of N15° ± 33°E, which closely matches the spreading direction of the Eurasian and North American plates (~N16°E). These results are consistent with the presence of rift-parallel cracks that gradually close with depth, the preferential opening of which is controlled by the regional stress field. Lateral variations in the strength of shear wave anisotropy reveal that regions with the highest concentrations of earthquakes have the highest SWA values (~10%), which reflects the presence of significant brittle deformation. Disruption of the orientation of the fast axis of anisotropy around Askja volcano can be related to local stress changes caused by underlying magmatic processes.

The emplacement mechanism of the Deccan province in India had been argued by researchers to a great extent. One of the most favoured hypotheses is “” facilitated by major pre or syn-Deccan crustal extension i.e. the Deccan flood basalts are dyke fed. Determination of flow direction, not only provides indirect evidence in proving or disproving the hypothesis, it also provides clues on its association with a mantle plume, depth of the feeder chambers, etc. In this paper, we have studied Nandurbar-Dhule (DND) Deccan dyke swarm (~210 mappable dykes) from Western India, that intruded compound basaltic (older than dykes) lava flows. Multiple oriented samples were collected from fourteen dykes of the swarm and their magnetic fabrics were delineated by Anisotropy of Magnetic Susceptibility (AMS) technique. The study was complemented by petrography and rock magnetic analysis to decipher the magnetic mineralogy and domain structure. AMS analysis suggests that most of the studied dykes display inclined/lateral flows which are likely in most large dyke swarms. Moreover, the cumulative flow geometry suggests the dominance of polycentric flow i.e. there were multiple magma sources and there were no preferable flow direction. Our results are strongly in line with the geochemical and isotopic signatures (that also establishes lateral, polycentric flow and indicates that the dykes are feeders to the younger Deccan flow) found independently by other groups of researchers. Finally, we discuss the merit of “eruption through fissures” hypothesis and its likely association with a mantle plume in the light of our results.