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Three-dimensional finite-element models, which can handle the stress perturbations caused by subsurface mechanical heterogeneities and fault interactions, have been combined with the finite source inversion to estimate the coseismic slip distribution over the fault plane. However, the mesh grid for discretizing the governing equations in the finite-element model significantly affects the numerical accuracy. In this study, we performed kinematic finite source inversion with idealized (regular observation point array; M1A–M1D) and regional (GEONET, GPS Earthquake Observation Network System stations in Japan; M2A–M2H) models with different mesh sizes to quantitatively analyse the effect of the mesh grid size around the fault plane on the inverted fault slip distribution. Synthetic observation data vectors obtained from the finest models (M1A and M2A) are compared with those from the coarser models (M1B–M1D and M2B–M2H), which were adopted to construct Green's function matrix. We found that the coarser mesh models derived a smaller surface displacement, leading to a decrease in the norm of Green's function matrix, which in turn influences the fault slip magnitude from the finite source inversion. Finally, we performed the source inversion for the fault slip distribution of the 2011 M w 9.0 Tohoku–Oki earthquake using the coseismic surface displacements recorded at the GEONET and seafloor stations and finite-element modelling. By reducing the mesh size on the fault, we confirmed that the estimated magnitude of fault slip converged to approximately 80 m, which is consistent with the range of fault slip amounts from previous studies based on the Okada model. At least 0.88 million total domain elements and a 6.7 km2 mesh size on the fault plane with an area of 240 × 720 km2 are required for the convergence of the fault slip. Furthermore, we found that the location of the maximum fault slip is less sensitive to the mesh size, implying that source inversion based on a coarse mesh model (i.e. less than 0.5 million elements and > ∼60 km2 mesh size) can quickly provide the rough fault slip distribution. [ABSTRACT FROM AUTHOR]

The granular behaviors of shallow Earth materials are associated with brittle deformations and mass transport along the surface and fault zones. Green strain has been adopted to quantitatively analyze the fold‐and‐thrust belt and horst‐and‐graben discrete element (DE) models driven by contractional and extensional forces, respectively. Deriving Green strain from DE models is challenging because of the need for precise mapping of the discrete particle displacement onto differentiable meshes. Here, we developed a new Green strain calculation methodology, the implicit global‐finite element method (IG‐FEM), which inverts a global matrix to reflect the interconnectivity of all particles. The IG‐FEM obtains strain quantities associated with particles to prevent an information loss, for example, displacement, at particle positions. We validated the accuracy of IG‐FEM compared to the conventional strain analysis scheme for DE model, finite difference method (FDM), by estimating the relative root mean square error from analytical solutions for a given mathematical transformation. On average, the IG‐FEM and the FDM show 2.8% and 17.4% relative root mean square errors, respectively. Furthermore, the strain quantities in the fold‐and‐thrust belt and horst‐and‐graben DE models were computed. The strain patterns of the IG‐FEM are more consistent with the particle spin distribution, which is noninterpolated information of the DE models. We present the potential benefits of the IG‐FEM for assessing strain‐related values such as stress, pore pressure, and seismic velocities within brittle deformation zones. The IG‐FEM is applicable in analog models and geodetic surveys to extract strain from discrete displacement data. Plain Language Summary: Understanding brittle structures at shallow depths is essential for estimating failure potentials. The discrete element method (DEM) is a particle‐based numerical technique that simulates brittle and plastic deformations induced by particulate flow. However, continuum strain analysis is difficult due to the discontinuous characteristics of the DEM. We propose a new particle‐wise Green strain tensor calculation method, namely, the implicit global‐finite element method (IG‐FEM). The IG‐FEM directly obtains Green (finite) strain tensor components by building a global matrix reflecting the local connectivity of particles. We also validate the accuracy of the IG‐FEM by measuring errors with the exact solutions in the analytical coordinate transformation. To verify the effectiveness of the IG‐FEM in the discrete element (DE) models, we conduct comparative studies with the finite difference method (FDM), which is popular for analyzing strain in the geological application of the DEM. The IG‐FEM‐induced strain shows a better consistency with the particle rotation distribution than strains derived by the FDM in the fold‐and‐thrust belt and horst‐and‐graben models. This method might be helpful for accurately including strain‐induced mechanisms in DE models by computing differential stresses and pore pressure in brittle and plastic deformations that show small‐scale strain heterogeneity. Key Points: We developed a new Green strain calculation methodology, an implicit global finite‐element method (IG‐FEM)Minimized interpolation processes of the IG‐FEM lead to highly accurate Green strain, which reflects particle behaviorThe IG‐FEM captures the strain heterogeneity in fold‐and‐thrust belt and horst‐and‐graben systems modeled by the discrete element method [ABSTRACT FROM AUTHOR]

Stress interaction among many faults in earthquake prone region is strongly affected by the spatial distribution of faults. To build a robust Machine Learning (ML) algorithm for finding hidden relationships between fault distribution and its controlling factors, the performance of ML in dependence of various parameters, such as the complexity and data size of the fault distribution, needs to be investigated. We have, therefore, developed an ML algorithm by combining Principal Component Analysis (PCA) with a Random Forest (RF) to unveil the controlling factors on seismic fault distribution. We synthesized fault images for training of RF classifier ND (> 10,000) fault images, which scattered the faults in a square with R km R km. R, ranging from 200 km to 600 km, is a controlling factor of fault distribution. PCA extracts the dominant features of the seismic fault images to supply the refined training data to the RF. This leads to a dimensional reduction of the data. We tested the influence of the number of principal components (NP) on PCA performance in retaining the information. Larger and more variable R values (i.e., a more complicated fault distribution) with larger amounts of training data required more principal components for a full preservation of the original data. We quantified the optimized NP/ND ratio for an efficient RF classifier, which was about ∼0.1 for the evaluating efficacy of the PCA. This showed that the RF classifiers is effective in predicting R values depending on the fault zone with R km R km and not on specific fault locations. We propose that a small NP, equivalent to ∼10% of the training data, suffices for training accurately RF classifier for fault distributions, which can reduce the complexity of fault distribution to understand stress interaction among many faults. [ABSTRACT FROM AUTHOR]

Carbon dioxide emissions from dolomite decarbonation play an essential role in the weakening of carbonate faults by lowering the effective normal stress, which is thermally activated at temperatures above 600-700 °C. However, the mechanochemical effect of lowcrystalline ultrafine fault gouge on the decarbonation and slip behavior of dolomite-bearing faults remains unclear. In this study, we obtained a series of artificial dolomite fault gouges with systematically varying particle sizes and dolomite crystallinities using a high-energy ball mill. The laboratory-scale pulverization of dolomite yielded MgO at temperatures below 50 °C, indicating that mechanical decarbonation without significant heating occurred due to the collapse of the crystalline structure, as revealed by X-ray diffraction and solid-state nuclear magnetic resonance results. Furthermore, the onset temperature of thermal decarbonation decreased to ~400 °C. Numerical modeling reproduced this two-stage decarbonation, where the pore pressure increased due to low-temperature thermal decarbonation, leading to slip weakening on the fault plane even at 400-500 °C; i.e., 200-300 °C lower than previously reported temperatures. Thus, the presence of small amounts of low-crystalline dolomite in a fault plane may lead to a severely reduced shear strength due to thermal decomposition at ~400 °C with a small slip weakening distance. [ABSTRACT FROM AUTHOR]

Buoyant trench sediment generates an isostatic restoring force that opposes the slab pull of subducting plates; however, the influence of this force on subduction dynamics is poorly understood. Here, we performed three‐dimensional free subduction simulations adopting a variety of sediment distributions along a trench to investigate the correlation between trench motions and heterogeneous buoyant forces. Two endmembers, sediment‐rich and sediment‐starved centers, induced convex and concave trenches, respectively. The trench curvatures obtained from the natural subduction zones are well constrained by our models over wide magnitudes (1–9 km) and wavelengths (100–400 km) of deficient and excess sediments. Conversely, a uniform sediment distribution leads to an extremely narrow range of trench curvatures. These results imply that trench sediment contributes significantly to deviated curvatures along trench strikes. Finally, we observed stress localization at shallow slab hinges that lie beneath abundant sediments, clarifying the relationship between sediment thickness and subduction earthquakes. Plain Language Summary: The role of trench sediment in subduction dynamics as a lubricant or restoring force against denser oceanic crust remains controversial. Buoyant sediment induces a restoring force and variations in sediment thickness may lead to laterally complicated force balances. However, the effect of variations in sediment distribution along strikes on subduction dynamics is underexplored. We conducted three‐dimensional free subduction modeling to analyze the factors that affect trench morphology and stress states within the subducting slab. Our results show that trench motion is strongly affected by differences in local isostatic restoring forces associated with sediment thickness variations. Locally thin trench sediment leads to a more rapid trench retreat and vice versa. The resultant differential trench motion along strike yields complicated trench shapes which exhibit a wide range of curvatures. By comparing the trench curvatures derived from our models to those obtained from natural subduction zones, we confirmed that the models with differential sediment distribution explained the patterns observed in major subduction zones. In contrast, models with uniform sediment thickness did not reflect natural trench curvature. Our study provides a fresh perspective on the trench shape of subduction zones (e.g., the Tonga‐Kermadec) with highly variable along‐strike sediment thickness. Key Points: We performed three‐dimensional free subduction simulations of trenches with variable along‐strike sediment distributionsLocally excessive and deficient trench sediments induce convex and concave trenches, respectivelyThe models with differential sediment distributions explain a wide range of trench curvatures of modern subduction zones [ABSTRACT FROM AUTHOR]

Our understanding of the seismicity of continental interiors, far from plate margins, relies on the ability to account for behaviours across a broad range of time and spatial scales. Deformation rates around seismic faults range from the slip-on-fault during earthquakes to the long-term viscous deformation of surrounding lithosphere, thereby presenting a challenge to modelling techniques. The aim of this study was to test a new method to simulate seismic faults using a continuum approach, reconciling the deformation of viscoelastoplastic lithospheres over geological timescales. A von Mises yield criterion is adopted as a proxy for the frictional shear strength of a fault. In the elastoplastic fault models a rapid change in strength occurs after plastic yielding, to achieve stress–strain equilibrium, when the coseismic slip and slip velocity from the strain-rate response and size of the fault are calculated. The cumulative step-function shape of the slip and temporally partitioned slip velocity of the fault demonstrated self-consistent discrete fault motion. The implementation of elastoplastic faults successfully reproduced the conceptual models of seismic recurrence, that is strictly periodic and time- and slip-predictable. Elastoplastic faults that include a slip velocity strengthening and weakening with reduction of the time-step size during the slip stage generated yield patterns of coseismic stress changes in surrounding areas, which were similar to those calculated from actual earthquakes. A test of fault interaction captured the migration of stress between two faults under different spatial arrangements, reproducing realistic behaviours across time and spatial scales of faults in continental interiors. [ABSTRACT FROM AUTHOR]

In the complicated force equilibrium of subduction dynamics, the slab pull resulting from the negative buoyancy of the lithosphere is considered the primary driving force of plate tectonics. In contrast, the isostatic restoring force due to lighter materials covering the oceanic crust (e.g., sediment) has been recognized as a relatively minor contributor. However, as the restoring force counteracts the gravitational pull, the resultant interaction has the potential to control the force balance governing the subduction system. Here, we conducted a series of three-dimensional viscoelastic-free subduction simulations with varying sediment distributions, thicknesses, and densities. We found that a higher restoring force suppressed the trench retreat and decreased the trench velocity. The trench curvatures increased with a high differential restoring force along the trench strike over time. Our results consistently showed a negative correlation between the effective slab pull and the isostatic restoring forces. Moreover, the magnitude and distribution of the isostatic restoring force along the trench strike determined the deviatoric stress level and location of the stress concentration within the subducting slab. We also found that locally abundant sediment margins may lead to a high deviatoric stress in the trench, which is associated with the occurrence of large earthquakes. We argue that sediment buoyancy can significantly affect the subduction kinematics and dynamics to a greater degree than previously suggested. Our findings provide fresh insights into the development of a global predicted velocity model, that reflects the effect of the isostatic restoring force, and provides a better understanding of subduction earthquakes. • We developed a systematic 3D subduction model to analyze sediment buoyancy. • Degree and distribution of isostatic restoring force control subduction kinematics. • Sediment buoyancy strongly affects stress state and slab pull in subducting slab. [ABSTRACT FROM AUTHOR]

We use finite element modeling to investigate on the stress loading-unloading cycles and earthquakes occurrence in the plate interiors, resulting from the interactions of tectonic plates along their boundary. We model a visco-elasto-plastic plate embedding a single or multiple faults, while the tectonic stress is applied along the plate boundary by an external loading visco-elastic plate, reproducing the tectonic setting of two interacting lithospheres. Because the two plates deform viscously, the timescale of stress accumulation and release on the faults is self-consistently determined, from the boundary to the interiors, and seismic recurrence is an emerging feature. This approach overcomes the constraints on recurrence period imposed by stress (stress-drop) and velocity boundary conditions, while here it is unconstrained. We illustrate emerging macroscopic characteristics of this system, showing that the seismic recurrence period τ becomes shorter as Γ and Θ decreases, where Γ = η I / η L , the viscosity ratio of the viscosities of the internal fault-embedded to external loading plates, respectively, and Θ = σ Y / σ L the stress ratio of the elastic limit of the fault to far-field loading stress. When the system embeds multiple, randomly distributed faults, stress transfer results in recurrence period deviations, however the time-averaged recurrence period of each fault show the same dependence on Γ and Θ , illustrating a characteristic collective behavior. The control of these parameters prevails even when initial pre-stress was randomly assigned in terms of the spatial arrangement and orientation on the internal plate, mimicking local fluctuations. Our study shows the relevance of macroscopic rheological properties of tectonic plates on the earthquake occurrence in plate interiors, as opposed to local factors, proposing a viable model for the seismic behavior of continent interiors in the context of large-scale, long-term deformation of interacting tectonic plates. [ABSTRACT FROM AUTHOR]

The East Sea (Sea of Japan) is a back–arc basin that underwent a complex deformation history associated with the relative motions of major tectonic plates. Constraining the crustal composition and rheology of the Ulleung Basin in the East Sea is essential for understanding back–arc basin dynamics. We perform finite element modeling using a wide range of rheologies (i.e., oceanic/continental crust and Moho temperature) to analyze small sedimentary buckling structures with wavelengths of ∼60–70 km and amplitudes of ∼150–200 m observed in the Ulleung Basin. When a high temperature (i.e., 570–640 °C) is adopted at Moho (depth of 12 km), both models with oceanic and continental crusts show surface topographies similar to the buckled morphology observed in the region. Furthermore, our new finding based on the numerical modeling constrains the stress of the lithosphere beneath the western margin of the East Sea. The depth–integrated stresses of the models that produce the buckling structures are <1.5 TN/m, which is much lower than those observed at plate boundaries. Thus, we argue that the Ulleung Basin does not fully sustain far–field tectonic stress propagation from its major trenches into the Korean Peninsula. The findings of this study suggest a need for further exploration of internal factors that may influence intraplate faults in SE Korea. • We perform 2D basin modeling to investigate the buckling structure in the East Sea. • Buckling geometry is more sensitive to the Moho temperature than to crustal composition. • The models with low strength are consistent with the observed buckling structure. [ABSTRACT FROM AUTHOR]

Using numerical modeling we show the emergence of cyclic slip behavior of faults from stress feedback through an idealized fault, its surrounding plates and far-field tectonic stress. The tectonic stress is exerted on the fault through a force applied along an idealized plate margin, acting on the fault, resulting from the interactions of viscous embedding and external plates. We find that, in such coupled system, the interaction of plates results into feedback with periodic deformation, slip along the fault and episodic plate margin motions. The viscosity of the embedding and loading plates primarily control the stress-loading time and hence the slip recurrence interval. For an Earth-like range of lithospheric viscosities, we derive a power-law with negative exponent, −0.99 to −0.5, scaling the recurrence period with loading-rate, providing an explanation for the observables from paleoseismology and geodesy. The feedback between single fault and far-field stress that arises from interactions of deforming plates provides a context to understand the earthquake cycle within continents, while reconciling the short-term seismic deformation to the long-term plate tectonics frame. [ABSTRACT FROM AUTHOR]

We conducted a two-dimensional numerical model to analyze the generation of tectonic over-pressure, which is a positive deviation from lithostatic pressure, for deep slabs which are anchored at the 660 km phase boundary. The formation of the ductile shear zone under a compressional tectonic setting induces tectonic over-pressure. We first propose that an apparent shear zone originated from an elastic heterogeneity in the phase loop, which is the two-phase (i.e., olivine and wadsleyite) coexistence interval around the 410 km boundary within subducting oceanic lithospheres, can cause tectonic over-pressure with a range from 0.3 to 1.5 GPa. This over-pressure significantly impacts the formation of the olivine–wadsleyite phase transition. The flattening of the olivine–wadsleyite interface by over-pressure is well-resolved. Therefore, we argue that the over-pressure should be applied when analyzing the phase boundary within the subducting lithosphere. Our results provide a new insight on the interplay among the phase transition, shear zone formation and tectonic over-pressure. [ABSTRACT FROM AUTHOR]

SUMMARY Viscoplasticity has been considered to be a dominant element in causing the nucleation of shear instability leading to lithospheric weakening. Here, we propose that a simple contrast in shear moduli may be sufficient for explaining the fast timescale asymmetric shear instability in a bimaterial setting. Not much attention has been paid to heterogeneous elasticity in geodynamical modelling because it is dominant only for short timescales. Up to now, no studies have been made on asymmetric shear instability induced by elastic modulus contrast. Thermal-mechanical numerical simulations based on high-resolution (from 0.4 km × 0.4 km to 0.2 km × 0.4 km meshes) finite-element methods were performed to understand the effects of shear modulus contrast on inducing asymmetric instabilities. Strain-rate and stress-dependent rheology are used with a wide range of activation energy 0-850 kJ mol-1 for all models. Numerical results with enough shear modulus contrast show asymmetric shear instability, which is generated around the interface and then propagates across the interface. Two parts of the lithosphere with different shear moduli (stiff for higher and soft for lower shear modulus lithospheres), which are simply connected to each other without a pre-defined weak zone, were compressed at a constant rate of 2 cm yr-1. Having different shear modulus is justified by chemical heterogeneity of geological minerals and their pressure-temperature dependence. To explore the dynamical effects generated by the contrast in the elastic modulus, the shear modulus of the soft lithosphere is fixed at 32 GPa, whereas that of stiff lithosphere is increased systematically from 32 up to 640 GPa. We also examined the role of activation energy (0-850 kJ mol-1) on the geometrical pattern and the initiation time of asymmetric shear localization. The shear modulus contrast has to be close to two for triggering asymmetric shear instability and is found to be by far a more important controlling factor in causing shear instability than activation energy of the creep law. The instability develops rapidly between 250 000 and 500 000 yr after deformation begins, and thermal weakening in the shear zone is greater, when a stronger shear modulus contrast is prescribed. Our work suggests that initiation of lithosphere-scale asymmetric instability would be faster than previous considerations. Our finding stresses that naturally occurring shear modulus contrast has also important impact on many geological problems related to bimaterial instability. [ABSTRACT FROM AUTHOR]

Fault gouge, located in highly deformed fault cores, shows substantial particle size reduction and loss of crystallinity, which could affect the physicochemical properties and thus control the slip behavior and earthquake stability of a fault. To systematically investigate the effect of deformed fault gouge on fault slip behavior in laboratory-scale experiments, a fault gouge analog with variable particle size and crystallinity is required. However, the systematic study for formation of a fault gouge analog (i.e., controlling the particle size and crystallinity) was not performed well. In this study, we investigated the effect of the rotation speed of a high-energy ball mill on particle size reduction rate and degree of amorphization. As the rotation speed increased from 500 to 2000 rpm, the comminution rate linearly increased, and reached a reduced particle size limit. The degree of amorphization and its rate also increased with increasing rotation speed. Upon grinding, the X-ray diffraction (XRD) peaks markedly decreased and reached critical amorphization points within 120 min, except for the case of grinding with a rotation speed of 500 rpm. Talc ground with a rotation speed of 500 rpm did not reach steady-state in mechanical amorphization after 360 min of grinding, thus necessitating prolonged grinding for further amorphization. A comparison of talc powders having similar specific surface areas, but ground at different rotation speeds, shows that grinding with a higher rotation speed for a shorter duration preserves the crystalline structure relatively well compared with grinding at a lower rotation speed for a longer duration. These results indicate that optimizing the grinding rotation speed facilitates the formation of talc fault gouge analogs with systematically varying particle size and crystallinity. The specific surface area of talc increased from 6.1 to 365 m2/g, and the degree of crystallinity decreased from approximately 75% to 11%. Our results indicate that an artificial talc fault gouge can be prepared by varying the particle size and crystallinity using a high-energy ball mill. [ABSTRACT FROM AUTHOR]

Edge-driven convection, which affects partial melting, intraplate volcanism, and dynamic topography, is small-scale convection that occurs along a lithospheric keel with a sharp contrast in lithospheric thickness. Various factors, including Rayleigh number, lateral mantle temperature heterogeneity, and geometry of the keel, influence the edge-driven convection, and the correlation between edge-driven convection and surface expressions (dynamic topography and volcanism) is complicated. We performed a finite element study to quantify the effects of these factors on dynamic topography and partial melting. We found that the dynamic topography is more prominent when a strong edge-driven convection cell develops, which corresponds to homogeneous mantle temperatures and the absence of mantle wind. In contrast, the development of edge-driven convection cells and dynamic topography near the lithospheric keel are hindered when the mantle temperature is strongly heterogeneous (laterally varying ~280 K). This indicates that a large lateral contrast in mantle temperature results in a strong mantle wind that may prevent the development of edge-driven convection cells. An increase in the Rayleigh number results in more vigorous convection and enhances partial melting. Our study shows that the location of volcanic activity at craton edges and passive margins can be reproduced in models with weakly heterogeneous mantle temperature for given mantle viscosity. The existence of a strong mantle wind (e.g., related to subducting slabs or mantle plumes) may inhibit the formation of an edge-driven convection cell and its related partial melt near a lithospheric keel. However, mantle conditions with weak temperature heterogeneity (<~14 K) or high mantle viscosity (>17×1019 Pa∙s), which corresponds to the Rayleigh number of 1.8×106, do not induce partial melts despite the development of edge-driven convection cells. Our model parametrized the condition and location of edge-driven convection cells and partial melts, which can contribute to understanding anomalous intraplate volcanisms, such as in Jeju Island south of the Korean Peninsula and the Tanzania Craton near the East African Rift. • Small lateral thermal heterogeneity causes localized edge-driven convention. • Topography increases and decreases due to upwelling and downwelling of EDC, respectively. • Thermal heterogeneity has promoting and suppressing effects on partial melting at lithospheric edge. • Strong mantle wind prevents the localization of mantle partial melting near lithospheric edge. • Strict range of thermal heterogeneity is needed for partial melting at lithospheric edge. [ABSTRACT FROM AUTHOR]

Numerical simulations provide an improved understanding of the evolution and core formation processes of terrestrial bodies. The differentiation of silicate and iron metal has been simulated by solving the two-dimensional Stokes equation using either the vector or potential method. To describe the realistic geometry of planetesimals and planets, the development of a 3D model is necessary. Here, we developed a vector method model implemented in FEniCS project via scripting the weak forms of governing equations. Subsequently, we compared the solutions of the vector method models with those of the benchmark potential method implemented in Python. Three cases were modeled using the two methods and confirmed for consistency to verify the feasibility of developing a 3D model for core formation. Case 1 corresponds to planetary evolution triggered by impact heating in early terrestrial bodies with a homogeneous metal fraction. The vector method developed in the current study showed the consistency with the potential methods. In Case 2, the model mimicked a scenario depicting post-evolutionary impact heating by assuming heterogeneous metal fractions. The results of Case 2 simultaneously represent the behavior of the solid mixture based on the density contrast and multiphase flow of the solid matrix and metallic pores. The checkerboard test (Case 3) used to evaluate the resolution of the numerical model as a function of the heat source size also indicated identical spatial resolutions for both methods. In all cases, two methods simulated identical physical behaviors, indicating that a three-dimensional model can be developed using the vector method. The 2D FEM vector method developed in this study was effectively utilized to simulate the advection scheme, showing the fast descent of metal phases and relatively slower silicate phases. We extended the 2D FEM vector method to calculate the velocity fields of silicate, Darcy, and iron metal in a 3D model with an impact heating case (similar to Case 1). The 3D results show that the velocity of fluid metal in 3D model is faster than that in 2D model, suggesting the difference in the resistance to viscous flow depending the dimension of model. Our 3D vector method, implemented in FEniCS, demonstrates the numerical prospect of the methods necessary to model the multiphase fluid dynamics of a 3D planetary evolution. [ABSTRACT FROM AUTHOR]

The growth mechanism of the Tibetan Plateau, postulated by a number of hypotheses, remains under intense debate. Our analysis of recent satellite‐based gravity model reveals that Tibetan lithosphere has been decoupled and folded. It is further evidenced by the existence of crustal melts and channel flow that have been observed by seismic and magnetotelluric explorations. Based on 3D geodynamic simulations, we elucidate the exact buckling structures in the upper crust and lithospheric mantle: at mixed wavelengths between ∼240 and ∼400 km, the lower crustal viscosity is smaller than ∼1019 Pa·s, implicating weak lower crustal flow beneath the Plateau. This mixed wavelength is consistent with the result of our inverse gravity modeling. Our results facilitate a new plausible hypothesis that the decoupled lithospheric folding mechanism can explain the growth mechanism of the anomalously thick and wide Tibetan Plateau by conflating our idea and contemporary hypothesized scientific findings. Plain Language Summary: The Tibetan Plateau, known as the Roof of the World, is the highest and largest Plateau on Earth, whose formation involves complex and active geodynamic processes since the Late Miocene. Here we emphasize the importance of decoupled lithospheric folding and its geodynamic process that has not yet been fully considered in the contemporary hypotheses on the origin of Tibetan Plateau's formation. The deep‐seated folding structure modeled using the latest satellite gravimetry shows a structure consistent with the plate tectonic setting, which allows rocks to melt easier and flow in the lower crust underneath the Tibetan Plateau. Our hypothesis was further tested and validated by three‐dimensional numerical simulations, revealing the decoupled lithospheric folds in the collisional tectonic setting. Our study is consistent with the existence of partial melting and flow channels of the Tibetan lower crust previously discovered by geophysical explorations. Further it makes it easier to explain the morphological characteristics, magma of crustal origin, and in particular, the mass transport process in the lower crust, which is the most important factor in the formation processes of the Tibetan Plateau, than the indentation process of the strong lithosphere. Key Points: Gravity field and Steady‐State Ocean Circulation Explorer (GOCE) gravity mission detected signals of upper crust in the Tibetan Plateau, which reveals the decoupled folding of the lithosphereThe decoupled folding process provides an alternative explanation of Tibetan Plateau's anomalously thick crust and flat topographyOur 3D viscoelastic numerical modeling explains the wavelenths of the decoupled folding beneath the Tibetan Plateau [ABSTRACT FROM AUTHOR]

Initiation of subduction is rarely encountered in modern tectonic environments due to its ephemeral and destructive nature. We report the geological and geophysical evidence indicating a transitional phase from buckling to embryonic subduction along the eastern Korean margin. The transition appears to be caused by compressional reactivation of the strike-slip boundary between the continental (Korean Peninsula) and oceanic (Ulleung Basin) crusts since the Early Pliocene. Evidence for compressional reactivation includes (1) a west-dipping major thrust and coincident crustal buckling of the Ulleung Basin; (2) an east-west structural asymmetry inferred from the gravity anomaly and P-wave tomography; and (3) ongoing crustal uplift and high-angle faults along the eastern Korean margin. The juxtaposition of underthrusting and buckling of the crust in the Ulleung Basin, and its associated ubiquitous reverse faulting on the eastern Korean margin, imply the potential development of a new subduction system along the western margin of the East Sea (Japan Sea). We propose that the East Sea comprises two incipient subduction margins (i.e., the Korean and Japanese sides), which are now competing to reach a self-sustaining subduction stage. [ABSTRACT FROM AUTHOR]

[Display omitted] • Mt. Hoam syenite in Apdong deposit intruded and immediately after mineralized at Silurian. • Dancheon Igneous complex is divided into Neoproterozoic western and Middle Paleozoic eastern parts. • The source material of Mt. Hoam syenite was formed from the pre-existing Neoproterozoic source. The Apdong Nb-Ta deposit is hosted within the syenite and in the Hoamsan area in the northern part of the Imjingang Belt in North Korea. Our new sensitive high-resolution microprobe zircon U-Pb results reveal two stages of Neoproterozoic to Ordovician inherited cores (887 Ma to 465 Ma) and Silurian emplacement and mineralization (425.5 ± 7.4 Ma) events. The zircon grains from the Apdong syenite show typical magmatic or textureless and sponge-like hydrothermal domains. These textural analyses supported the rare earth element characteristics obtained from the laser ablation-induced coupled plasma mass-spectrometry analyses (LA-ICP-MS). Neoproterozoic magmatic activities reportedly occur in the Pyeongnam Basin, Imjingang Belt [present study], Gyeonggi Massif, and Okcheon metamorphic belt in the central part of the Korean Peninsula and China (North China Craton, Qinling Orogenic Belt, and South China Craton). Notably, the Caledonian mineralization events in the southeastern part of the South China Craton coincided with emplacement and mineralization ages from the Apdong syenite (425.5 ± 7.4 Ma). The LA multi-collector ICP-MS Hf isotope of zircons from the Apdong syenite yielded positive initial εHf values plotted along the Neoproterozoic crustal evolution path, indicating that the host rock of Nb-Ta ore was formed from the pre-existing Neoproterozoic source. The source materials of Neoproterozoic intrusives in the central part of the Korean Peninsula were generally derived from Mesoproterozoic depleted mantle sources. Considering the previously reported Hf isotopic results, the involvement of pre-existing crustal materials is more prominent in the Neoproterozoic intrusives in the southern part of the central Korean Peninsula, i.e., the Gyeonggi Massif, than in the northern part of the central Korean Peninsula, such as the Imjingang Belt and Pyeongnam Basin in the northern part of the central Korean Peninsula. [ABSTRACT FROM AUTHOR]

Abstract: Study Objective: To determine whether playing music or blocking noise can reduce bispectral index (BIS) values during propofol sedation. Design: Prospective, randomized, single-blinded study. Setting: Operating room. Patients: 63 ASA physical status I and II patients, aged 55 to 75 years, undergoing total knee replacement. Interventions: Patients were divided into three groups: noise, silence, and music. After induction of combined spinal-epidural anesthesia, sedation was begun with 1.2 μg/mL of propofol in a target-controlled infusion. In the silence group, patients'' ears were packed tightly to block ambient noise, whereas patient-selected music was applied to patients in the music group. Patients in the noise group were exposed to ambient operating room noise. Measurements: Bispectral index measurement was recorded 7 times during operation. Ambient room noise was recorded at the same time sequence. Main Results: Sound level was highest when the saw (T3, 80.25 dB) and the impact device (T4, 80.98 dB) were in use. Bispectral index scores in the silence group during those times (T3, 68.5 vs 76.9, P = 0.025, and T4, 67.6 vs 78, P = 0.005) were lower than in the noise group. However, BIS scores were similar in the noise and music groups. Preoperative anxiety level, postoperative comfort level, and pain scores were similar in all groups. Conclusion: Blocking noise is more effective than playing music in reducing BIS scores during propofol sedation in a noisy environment. [Copyright &y& Elsevier]