Lateral Heterogeneity Research Articles

Antipodal waveform observations of seismic waves diffracting and refracting at the base of Earth's outer core

We approach this analysis of the inner-outer core boundary (IOCB) with antipodal waveform data in the distance range 179.0°–180° to test the hypothesis whether propagation at the base of the outer core is commensurate with diffraction and/or refraction. The propagation paths observed cover about two-thirds of the IOCB surface. Seismic data from seven diameters are examined—Tonga to Algeria (station code TAM), Sulawesi to Amazon (PTGA), northern Chile to Hainan Island (QIZ), two between central Chile and the mainland China (XAN, ENH), and two diameters from New Zealand to both Portugal (PTO) and Spain (ECAL). The adequacy of global Earth models—both 1-D and 1-D core +3D mantle—in fitting the antipodal observations is found to be deficient. Lateral heterogeneity among the propagation paths are mapped and projected to the Earth's surface for context. We stack data to increase signal-to-noise, and model waveform data via the 3D spectral element method on the EarthSimulator4. With the exception of one path to ENH China, none of the global Earth models match amplitudes of diffracted waves or the stacked amplitudes relative to PKIKP, which travels along the antipodal diameter. Energetic arrivals observed in the waveform data set are modeled as a combination of refraction within a low velocity zone (LVZ) at the base of the outer core, and diffraction around this structure. The observations at the base of the outer core may be further subdivided between paths with a thin low velocity zone (QIZ, XAN, PTGA), and those with a thicker, slower LVZ (TAM). The former paths are characterized by a thin LVZ (20–50 km thick, layer–gradient, respectively) with a velocity of approximately 10.0 km/s. The second group of paths shows large amplitude, complicated waveforms for TAM, corroborated by data from PTO and ECAL. TAM waveforms are modeled with a negative gradient from 100 to 50–75 km thickness above the IOCB, to a basal velocity of 8.8 km/s at IOCB. We also modeled the prospect of non-zero rigidity at the bottom of the outer core, but found no evidence of sensitivity in the core data. The structures fitting the data correlate across the inner–outer core boundary, with a velocity anomaly in PKPbc data juxtaposed immediately above the TAM path beneath SE Asia. More generally, the TAM IOCB path when projected up to the core-mantle boundary (CMB) apparently aligns with regions between the large low shear velocity provinces (LLSVP) at the CMB. Other paths with thinner or negligible LVZ at the IOCB partially underlie the LLSVP when projected to the CMB.

Investigating the organisation of the asymmetric plasma membrane using a novel solvatochromic reporter.

The plasma membrane (PM) of an animal cell is a heterogenous mixture of lipids and proteins that exhibits both lateral heterogeneity and transverse asymmetry in composition. The complex mixture of lipid species with a range of headgroups and degrees of acyl-chain unsaturation influences the properties of the bilayer such as ordering and consequently the function of embedded membrane proteins. In this study, we have probed the presence of liquid-ordered (lo) domains in each leaflet of the PM and their transbilayer registry in live cells by designing a membrane localised probe that is sensitive to lipid order. This solvatochromic probe, C3L, uses Laurdan as a template and reports on changes in lipid order of complex lipid compositions such as Giant Plasma Membrane Vesicles (GPMVs), while exhibiting a preference for lo-domains. C3L distributes across both leaflets in the live cell membrane, regulated by flippases and scramblases and may be selectively and robustly confined to the inner leaflet after back extraction. C3L indicates the inner leaflet to be significantly disordered compared to the outer leaflet wherein the depletion of sphingomyelin (SM) leads to a more outer-leaflet restricted effect but phosphatidylserine (PS) depletion leads to effects on both leaflets, especially the inner leaflet. This suggests that PS and SM play different roles in building and maintaining domains and coupling them across the bilayer. Further, C3L reported lipid organisation indicates domains of smaller scale and broader order distribution in the PM of live cells at the same temperature compared to homogenous and disordered domains in GPMVs derived from them providing support for active de-mixing in membranes of living cells. Using this tool, we intend to explore the impact of membrane composition and cytoskeletal activity in tuning cellular signalling by regulating transbilayer properties of the PM.

Elucidating the phase behavior of ternary model membrane mixtures containing halogenated cholesterol analogues.

Cellular plasma membranes exhibit nanoscale lateral lipid heterogeneity, a feature that is thought to be central to their functionality. However, only a few biophysical methods are capable of detecting domains at sub-micron length scales. We recently showed that cryogenic electron microscopy (cryo-EM) can directly image phase separation in extruded liposomes due to its ability to resolve the intrinsic thickness and electron density differences of ordered and disordered phases. However, the contrast between these phases is poor compared to conventional fluorescence microscopy and is thus both a limiting factor and a focal point for optimization. Because the fundamental source of contrast is the spatial variation in electron density within the bilayer, lipid modifications aimed at selectively increasing the electron density of one phase might enhance the ability to resolve coexisting phases. To this end, we make use of a model membrane mixture of DPPC/DOPC/cholesterol, in which one hydrogen of the methyl group on the steroid ring of cholesterol is replaced by an electron-rich halogen atom. We use a variety of biophysical techniques including confocal fluorescence microscopy, FRET, and cryo-EM to examine phase behavior as a function of composition and temperature. We find that cryo-EM image contrast is increased in liposomes containing halogenated cholesterol as expected. However, the phase behavior of these mixtures is altered compared to mixtures containing native cholesterol providing a cautionary note that halogenated cholesterol has biophysical effects beyond increasing electron density.

Domain-induced dynamics in phase-separating lipid membranes.

Lipid membranes have a significant role in cells, not only defining the boundaries of cells and cell organelles but also playing an active role in cell functions, including the partitioning of proteins and the spatiotemporal regulation of signaling clusters. This is facilitated by the rich lipid diversity in cell membranes, which often results in unideal mixing and subsequent lipid phase-separation into lateral compositional heterogeneities or domains. Over the past few decades, structural measurements on such membranes have shed important light on the molecular mechanisms underlying domain formation. However, major information gaps still exist in our understanding of how domain formation affects the dynamics of lipid membranes, whether in the form of collective fluctuations or molecular motions. To address this outstanding question, we use neutron spectroscopy and molecular dynamics (MD) simulations that can selectively investigate the matrix dynamics in domain-forming membranes. Specifically, our studies are performed on binary mixtures of 1,2-dimyristoyl-sn-glycero-3-phosphocholine (DMPC) and deuterated 1,2-distearoyl-sn-glycero-3-phosphocholine (DSPC). Experimental results, obtained by neutron spin-echo spectroscopy and neutron backscattering spectroscopy, show that the formation and growth of rigid DSPC domains causes an effective slowdown in the bending fluctuations and diffusional dynamics of the otherwise fluid DMPC matrix. MD simulations on cognate bilayers suggest that the measured changes in the matrix dynamics are mediated by interfacial DMPC lipids that experience constrained diffusional jumps and longer residence times at the domain boundaries. Our findings present striking evidence of dynamic coupling between lipid domains and their surrounding lipid environment. More importantly, this interplay occurs on the nanosecond time scales of protein conformational changes and signaling events. Put together, the results suggest an intriguing mechanism by which domain formation can play a regulatory role in functional membrane processes.

FEATURES OF THE STRUCTURE AND EVOLUTION OF THE LOWER PARTS OF THE CONTINENTAL CRUST OF THE YAKUTIAN DIAMONDIFEROUS PROVINCE IN THE AREA OF THE UPPER-MUNA KIMBERLITE FIELD

Upper Muna kimberlite field) showed that the crust at different levels is composed of pyroxene, garnet-pyroxene crystalline schists and garnet-pyroxene gneisses. Exsolution textures in pyroxenes and amphiboles, granat rims around grains of ilmenite and pyroxenes indicate that the mineral associations of crystalline schists were formed during cooling at constant pressure. Р–Т equilibrium parameters indicate that garnet-pyroxene crystalline schists are present in the middle crust (P = 7–8 kbar), while garnet-pyroxene gneisses can be considered as rocks of the lower crust (P = 9–10.1 kbar). For the first time, sodalite was found in xenoliths of crystalline schists, which indicates the presence of brines with a high concentration of NaCl at the final stages of rock cooling. The determination of the U–Pb age of zircons testifies to the Neoarchean (2.7 Ma) tectono-thermal event, accompanied by the melting of the crust. In the garnet–pyroxene gneisses, the 1.9 stage is weakly manifistated. The obtained data confirm the earlier conclusion about the vertical and lateral heterogeneity of the crust of the Yakutsk diamondiferous province and the absence of dependence between the degree of crust reworking and spatial location relative to the main collision zones of the Siberian craton.

Mapping the Three‐Dimensional Nanostructure of the Ionic Liquid–Solid Interface Using Atomic Force Microscopy and Molecular Dynamics Simulations

AbstractIonic liquids (ILs) are a widely investigated class of solvents for scientific and industrial applications due to their desirable and “tunable” properties. The IL–solid interface is a complex entity, and despite intensive investigation, its true nature remains elusive. The understanding of the IL–solid interface has evolved over the last decade from a simple 1D double layer, to a 2D ordered interface, and finally a liquid‐specific, complex 3D ordered liquid interface. However, most studies depend solely on one technique, which often only examine one aspect of the interfacial nanostructure. Here, a holistic study of the protic IL–solid interface is presented, which provides a more detailed picture of IL interfacial solvation. The 3D nanostructure of the ethylammonium nitrate (EAN)–mica interface is investigated using a combination of 1D, 2D, and 3D amplitude modulated‐atomic force microscopy and molecular dynamics simulations. Importantly, it is found that the EAN–mica interface is more complex than previously reported, possessing surface‐adsorbed, near‐surface, surface‐normal, and lateral heterogeneity, which propagates at relatively large distances from the solid substrate. The work presented in this study meaningfully enhances the understanding of the IL–solid interface.

Directly imaging emergence of phase separation in peroxidized lipid membranes

Lipid peroxidation is a process which is key in cell signaling and disease, it is exploited in cancer therapy in the form of photodynamic therapy. The appearance of hydrophilic moieties within the bilayer’s hydrocarbon core will dramatically alter the structure and mechanical behavior of membranes. Here, we combine viscosity sensitive fluorophores, advanced microscopy, and X-ray diffraction and molecular simulations to directly and quantitatively measure the bilayer’s structural and viscoelastic properties, and correlate these with atomistic molecular modelling. Our results indicate an increase in microviscosity and a decrease in the bending rigidity upon peroxidation of the membranes, contrary to the trend observed with non-oxidized lipids. Fluorescence lifetime imaging microscopy and MD simulations give evidence for the presence of membrane regions of different local order in the oxidized membranes. We hypothesize that oxidation promotes stronger lipid-lipid interactions, which lead to an increase in the lateral heterogeneity within the bilayer and the creation of lipid clusters of higher order.

Imaging the subducting slab and mantle upwelling under the Japan islands revealed by double-difference tomography

In this paper, we collected the seismic phase arrival data of 14,033 local natural earthquakes above magnitude 3.0 recorded by 435 seismograph stations in the study area provided by the International Seismological Centre (ISC), covering the period from January 2011 to April 2020. We selected the first arrival P- and S-wave arrival time data and obtained 281,859 P- and 112,926 S-wave absolute arrival times and 528,250 P-differential and 207,968 S-differential arrival times. Then we determined 3-D P and S wave velocity structures from the Japan Trench to the back arc area under the Japan Islands by using double-difference tomography method. The results show strong lateral heterogeneities under the forearc region. The subducting Pacific slab is imaged clearly as a high-velocity (high-V) faster than the surrounding mantle. Low-velocity (low-V) zones are imaged in the mantle wedge with significant along arc variations under the volcanic front. The vertical section shows that the low velocity zone extends to a depth of approximately 70–150 km below the arc. The crust and mantle wedges beneath the front and back arcs of the volcanoes reveal a low-V anomaly, the likely main source of which is the partial melting of plate and mantle wedge material. Referring to the previous results of plate dehydration, mineral composition and thermal state, it is found that fluids play a crucial role in the arc magmatism and plate melting of mantle wedge behind Japan Trench. The fluids brought down by the Pacific subducting plate are released into the mantle wedge by dehydration and subsequently transported upward by the upwelling flow in the mantle wedge. The present results obtained using new and advanced imaging methods enrich the understanding of the velocity structure beneath Japan Islands, which may improve the understanding of the dynamic processes of subduction zones and mantle upwelling.

Aggregation of chlorophylls on plant thylakoid membranes using coarse-grained simulations.

Chlorophyll a (CLA) molecules in light-harvesting complexes are the most essential pigments for photosynthesis. Coarse-grained molecular dynamics simulations of CLA are carried out in plant thylakoid membranes at 293 K by varying the total lipid-to-CLA ratio using our previously derived coarse-grained model of CLA and MARTINI force fields for lipids. Our simulations show that CLA molecules dynamically form aggregates that break and reform. The lifetime of the dimer and the waiting time of the dimer formation follow bi-exponential distributions for the higher concentrations of CLA. The number of aggregates increases with an increasing concentration of CLA, where the aggregation is governed by van der Waals interactions. Our simulations suggest that selective lipids promote the formation of CLA aggregates in plant thylakoid membranes. As the concentration of CLA increases, diacylglycerol and phosphatidylglycerol lipids with palmitoyl tails prefer to reside near the CLA aggregates, and the lipids with linolenoyl tails with higher levels of unsaturation move away from the aggregates. Such preferential locations of lipids result in increasing lateral heterogeneity in the order parameter and density with increasing CLA concentration. This induces more undulations in membranes, resulting in a lower bending modulus and area compressibility. Our work unfolds the mechanism of the formation of CLA aggregates and their effect on the structure of thylakoid bilayers. The study provides the foundation for a better understanding of more complex biophysical phenomena, such as photosynthesis and non-photochemical quenching, in the future.

Imaging and Manipulation of Plasma Membrane Fatty Acid Clusters Using TOF-SIMS Combined Optogenetics.

The plasma membrane (PM) serves multiple functions to support cell activities with its heterogeneous molecular distribution. Fatty acids (FAs) are hydrophobic components of the PM whose saturation and length determine the membrane's physical properties. The FA distribution contributes to the PM's lateral heterogeneity. However, the distribution of PM FAs is poorly understood. Here, we proposed the FA cluster hypothesis, which suggested that FAs on the PM exist as clusters. By the optogenetic tool translocating the endoplasmic reticulum (ER), we were able to manipulate the distribution of PM FAs. We used time-of-flight combined secondary ion mass spectrometry (TOF-SIMS) to image PM FAs and discovered that PM FAs were presented and distributed as clusters and are also manipulated as clusters. We also found the existence of multi-FA clusters formed by the colocalization of more than one FA. Our optogenetic tool also decreased the clustering degree of FA clusters and the formation probability of multi-FA clusters. This research opens up new avenues and perspectives to study PM heterogeneity from an FA perspective. This research also suggests a possible treatment for diseases caused by PM lipid aggregation and furnished a convenient tool for therapeutic development.

Optimization of cryo-electron microscopy for quantitative analysis of lipid bilayers

Cryogenic electron microscopy (cryo-EM) is among the most powerful tools available for interrogating nanoscale structure of biological materials. We recently showed that cryo-EM can be used to measure the bilayer thickness of lipid vesicles and biological membranes with subangstrom precision, resulting in the direct visualization of nanoscopic domains of different thickness in multicomponent lipid mixtures and giant plasma membrane vesicles. Despite the great potential of cryo-EM for revealing the lateral organization of biomembranes, a large parameter space of experimental conditions remains to be optimized. Here, we systematically investigate the influence of instrument parameters and image postprocessing steps on the ability to accurately measure bilayer thickness and discriminate regions of different thickness within unilamellar liposomes. This unique application of cryo-EM places particular demands on image acquisition optimization and analysis due to the facts that 1) each vesicle is a different size with different curvature, 2) the domains in each vesicle can be heterogenous in size, and 3) the random orientation of vesicles amplifies the variability of domain size in projected images. We also demonstrate a spatial autocorrelation analysis to extract additional information about lateral heterogeneity.

Efficient liposome fusion to phase-separated giant vesicles

Lateral phase heterogeneity in biomembranes can govern cellular functions and may serve as a platform for enrichment or depletion of membrane-anchored molecules. In this work, we address the question of how the process of membrane fusion is affected by the membrane phase state (fluid or gel) and by phase coexistence, as well as the effects of fusion-mediated incorporation of exogeneous lipids on phase separation. Our system is based on the fusion of cationic fluid large unilamellar vesicles (LUVs) composed of dioleoyl trimethylammonium propane (DOTAP) and dioleoyl phosphoethanolamine (DOPE) with neutral and anionic giant unilamellar vesicles (GUVs) composed of phosphatidylcholine and phosphatidylglycerol. By changing the lipid composition of the GUVs, we modulated the phase state and charge of the different phases (charged or neutral, fluid or gel) and identified systems in which we can target fusion to specific domains on phase-separated membranes. Fusion efficiency was quantified using fluorescence microscopy-based lipid and content mixing assays, and flow chamber devices were used to assess the real-time sequence of events of the fusion process. To investigate the bilayer thermal behavior, differential scanning calorimetry (DSC) experiments were performed on LUVs. The results show that fusion is extensive in single-component GUVs only for fluid and negatively charged acceptor membranes. On the other hand, in phase-separated GUVs, high fusion efficiency was observed even when the gel phase was anionic and phase separation somewhat increased the fusion efficiency. Extensive fusion led to dissolution of the gel domains as a result of extensive incorporation of lipids in the fluid state from the fusogenic liposomes. Altogether, these findings have the potential to unravel the important role of membrane phase state, phase separation, charge, and the effects of extensive fusion on membrane organization and may give insights in the regulation of the interactions between cells and liposomes that are used in drug delivery systems.

P-wave velocity structure in the crust and the uppermost mantle of Chao Lake region of the Tan-Lu Fault inferred from teleseismic arrival time tomography

Chao Lake is a Geoheritage site on the active Tan-Lu Fault between the Yangtze craton, the North China craton, and the Dabie orogenic belt in the southeast. This segment of the fault is not well constrained at depth partly due to the overprinting of the fault zone by intrusive materials and its relatively low seismic activity and sparse seismic station coverage. This study took advantage of a dense seismic array deployed around Chao Lake to delineate the P-wave velocity variations in the crust and uppermost mantle using teleseismic earthquake arrival time tomography. The station-pair double-difference with waveform cross-correlation technique was employed. We used a multiscale resolution 3-D initial model derived from the combination of high-resolution 3-D vS models within the region of interest to account for the lateral heterogeneity in the upper crust. The results revealed that the velocity of the upper crust is segmented with structures trending in the direction of the strike of the fault. Sedimentary basins are delineated on both sides of the fault with slow velocities, while the fault zone is characterized by high velocity in the crust and uppermost mantle. The high-velocity structure in the fault zone shows characteristics of magma intrusion that may be connected to the Mesozoic magmatism in and around the Middle and Lower Yangtze River Metallogenic Belt (MLYMB), implying that the Tan-Lu fault might have formed a channel for magma intrusion. Magmatic material in Chao Lake is likely connected to the partial melting, assimilation, storage, and homogenization of the uppermost mantle and the lower crustal rocks. The intrusions, however, seem to have suffered severe regional extension along the Tan-Lu fault driven by the eastward Paleo-Pacific plate subduction, thereby losing its deep trail due to extensional erosion.

Mantle Structure and Processes in Transition Zone of the Baikal Rift Zone

The velocity structure of the mantle under the Baikal Rift Zone (BRZ) is investigated with the P‑wave receiver functions (PRFs) for a group of 10 seismograph stations. The BRZ presents one of the world’s most active continental rift zones. The peculiarities of the BRZ include Cenozoic magmatism in the upper mantle of the southwestern part of the BRZ, which disappears in the central and northeastern parts. The analysis of seismic data reveals other indications of the significant lateral heterogeneity of the mantle beneath the BRZ. At half of the stations there is evidence of a sharp rise of the S velocity with depth at a depth of around 330 km, similar to the descriptions for the “X” or the “300-km” discontinuity. In the central and northeastern regions at depths from about 350 to 410 km there is a well pronounced low S velocity layer, which is practically missing in the southwestern part. The origin of this layer is apparently related to the upwelling and dehydration of wadsleyite in the transition zone. At depths from 500–600 to 660 km in the central and northeastern regions there is another low velocity layer that may be explained by the accumulation of garnetite in the process of subduction of the lithosphere of the Pacific. This layer is poorly pronounced in the southwestern region. The difference between the travel times of the P410s and P660s seismic phases (differential time) in the southwestern region (23.5 s) is close to the data for the standard model (Kennett, Engdahl, 1991). In the central and northeastern regions, the observed differential time is larger than the nominal time by 1.0 s. The rise of the differential time may be related to the cooling and/or hydration of the transition zone by the slabs of the subducted oceanic lithosphere. The obtained seismic data suggest a large role of processes of hydration and dehydration in the central and northeastern regions, however, this role is comparatively small in the southwestern region.

Shallow Ice‐Sheet Composite Structure Revealed by Seismic Imaging Near the West Antarctic Ice Sheet (WAIS) Divide Camp

AbstractSmall‐scale polar ice‐sheet composite structures can influence coarse‐grained climate models. For example, surface melting can hydro‐fracture the ice and may eventually lubricate the base. The drainage process will change the petrophysical properties of the subsurface and is predictable from high‐resolution seismic imaging. Ray‐based imaging methods, though limited by the approximations made, have mapped seismic velocities in 1D, but have yet to offer definitive information about the lateral heterogeneity. Here we use the wave‐equation‐based seismic imaging method to estimate shear‐wave velocities and to image an englacial reflector in 2D. We use 7‐day ambient‐noise data recorded by a linear array near the West Antarctic Ice Sheet (WAIS) Divide drilling site to perform the study. We obtain 2D vertical and horizontal shear‐wave velocity models and observe a lateral variation of the radial anisotropy along the acquisition line. The inverted velocity model is further used to estimate the thicknesses of firn‐air and firn layers. We also observe evident SH reflections and calculate the reflector image using robust zero‐offset imaging and a more precise reverse time migration imaging method. The imaged reflector is at about 1,700 m depth and is dipping to the southwest. We anticipate that a porosity change at that depth may cause this englacial seismic discontinuity near WAIS Divide. Our results demonstrate the feasibility of estimating the petrophysical properties of polar ice using seismic methods. We anticipate our work to be further used for understanding ice dynamics and thermodynamics, such as the stability of ice shelves, the retreat of the Antarctic ice sheet, and restoring the paleo‐sedimentary environment.

Cyclodextrins: Only Pharmaceutical Excipients or Full-Fledged Drug Candidates?

Cyclodextrins, representing a versatile family of cyclic oligosaccharides, have extensive pharmaceutical applications due to their unique truncated cone-shaped structure with a hydrophilic outer surface and a hydrophobic cavity, which enables them to form non-covalent host-guest inclusion complexes in pharmaceutical formulations to enhance the solubility, stability and bioavailability of numerous drug molecules. As a result, cyclodextrins are mostly considered as inert carriers during their medical application, while their ability to interact not only with small molecules but also with lipids and proteins is largely neglected. By forming inclusion complexes with cholesterol, cyclodextrins deplete cholesterol from cellular membranes and thereby influence protein function indirectly through alterations in biophysical properties and lateral heterogeneity of bilayers. In this review, we summarize the general chemical principles of direct cyclodextrin-protein interactions and highlight, through relevant examples, how these interactions can modify protein functions in vivo, which, despite their huge potential, have been completely unexploited in therapy so far. Finally, we give a brief overview of disorders such as Niemann-Pick type C disease, atherosclerosis, Alzheimer's and Parkinson's disease, in which cyclodextrins already have or could have the potential to be active therapeutic agents due to their cholesterol-complexing or direct protein-targeting properties.

Massive Spatial Well Clustering Based on Conventional Well Log Feature Extraction for Fast Formation Heterogeneity Characterization

Abstract Recent enhancements in computational capacity provide an opportunity for harnessing the enormous amount of reservoir data already acquired and extracting useful information for hydrocarbon exploration, development, and production. This article reports a three-step clustering technique to determine well groups based on subsurface geological heterogeneity using feature extraction, hierarchical ensemble clustering, and spatial mapping. The first step of the presented methodology is to group the wells into different clusters based on the formation rock composition and property features extracted from well logs using the expectation maximization algorithm. The one-dimensional (1D) stacking pattern of each well log curve is expressed through a two-dimensional (2D) transformation scheme. Thus, the clustering can capture the vertical stacking patterns of well logs, which is essential for reservoir heterogeneity characterization. This base clustering process generated a feature matrix which is further grouped through the hierarchical ensemble clustering in a latent space of well logs in the second step. Through the ensemble clustering, different clustering proposals obtained from the base clustering are integrated corroboratively to reflect a comprehensive feature of all studied logs. In the third step, the spatial clustering is performed based on the ensemble results, considering the spatial distances between well locations in the target area. The results of the 2D spatial map may provide insights into the sedimentary depositional environment in terms of the lateral geological heterogeneity features. Therefore, the proposed clustering technique can present a fast geological modeling method to integrate geological heterogeneity features presented in multiple well logs, which is not yet fully utilized in traditional geomodeling approaches. The results can also support further reservoir studies, such as petrophysical modeling, reservoir modeling, and fluid flow simulation studies.

The Influence of Sediments, Lithosphere and Upper Mantle (Anelastic) With Lateral Heterogeneity on Ocean Tide Loading and Ocean Tide Dynamics

AbstractOcean tide loading (OTL) and ocean tide dynamics (OTD) are known to be affected by Earth's internal structures, with the latter being affected by the self‐attraction and loading (SAL) potential. Combining the 3D earth models Lyon and LITHO1.0, we construct a hybrid model to quantify the coupled effect of sediments, oceanic and continental lithosphere, and anelastic upper mantle on OTL and OTD. Compared to PREM, this more realistic 3D model produces significantly larger vertical OTL displacement by up to 3.9, 2.6, and 0.1 mm for the M2, K1, and Mf OTL, respectively. Moreover, it shows a smaller vector difference of 0.1 mm and a smaller amplitude difference of 0.2 mm than PREM with OTL observations at 663 Global Navigation Satellite System stations, a confirmation of the cumulative effect due to these earth features. On the other hand, we find a resonant impact of wider extent and larger magnitude on OTD, especially for the M2 and K1 tides. Specifically, this impact is concentrated in the ranges 0–6 mm and 0–1.5 mm for M2 and K1, respectively, which is considerably larger than the impact on SAL (mostly in the ranges 0–2 mm and 0–1.0 mm, respectively). Since the effect on vertical displacement is at a similar level compared to the accuracy of modern data‐constrained ocean tide models that require correction of the geocentric tide by loading induced vertical displacements, we regard its consideration to be potentially beneficial in OTD modeling.

Fine‐Sediment Erosion and Sediment‐Ribbon Morphodynamics in Coarse‐Grained Immobile Beds

AbstractIn rivers, fine sediments are often transported over immobile coarse grains. With low sediment supply, they tend to aggregate in longitudinal ribbons. Yet, the long‐term evolution of such ribbons and the influence of immobile grains on the erosion of fine sediments are still not well understood. Flume experiments without sediment supply were therefore performed to investigate the erosion of an initially uniform fine‐sediment bed covering an immobile bed of staggered spheres through topographic and flow measurements. The topographic measurements yielded the spheres' protrusion above the fine sediment (P) and revealed long‐lived ribbons with ridges and troughs. The ridges are the main long‐term sediment source as the troughs are quickly eroded to a stable bed level resulting from the spheres' sheltering. The ridges stabilize with a spacing of 1.3 effective water depths, their number resulting from the integer number of wavelengths fitting into the effective channel width which excludes side‐wall accumulations. The ridges' erosion is damped by the local upflow of secondary current cells, which displaces the strongest sweep events above the bed. The upflow intensity is controlled by the ridges' height for low P, while for high P by the lateral roughness heterogeneity. The trends in erosion rates over ridges and troughs are similar and characterized by the following sequence of four regimes with increasing P: a drag sheltering, a turbulence‐enhancement, a wake‐interference sheltering, and a skimming‐flow sheltering regime. The critical P levels at the transitions are independent of the flow above the canopy, depending only on the geometrical configuration of the immobile bed.

Application of six-component ambient seismic noise data for high-resolution imaging of lateral heterogeneities

SUMMARY We develop a novel approach for imaging subsurface lateral heterogeneities using six-component (6C) ambient seismic noise data, consisting of three translational components and three rotational components. We first derive the 6C cross-correlation functions (CCFs) from ambient seismic noise data for surface waves and then apply the modified frequency Bessel (MF-J) transform to the 6C CCFs for surface wave dispersion curves. The phase velocities of Rayleigh and Love waves can be directly calculated from the 6C CCFs of a single pair of stations. Traditional array-based surface wave methods derive the surface wave phase velocity based on the presumption of a horizontally layered model. When this assumption breaks down due to the presence of, for example, dipping layer or heterogeneities, the resulting phase velocity can be severely smeared. By contrast, the proposed approach is not limited by the layered model assumption because it relies on single-point measurements to calculate the localized dispersion relations of the formation right beneath a receiver. Our numerical modelling results demonstrate that this approach is applicable to heterogeneous models and can image small-scale subsurface anomalies with very high lateral resolution.