Journal of Geophysical Research: Solid Earth最新文献

Surface heat flow (SHF) serves as a vital parameter for assessing the heat transfer from deep Earth to the surface, which can provide crucial insights into internal geodynamic processes. As the “roof of the world,” the Tibetan Plateau and its tectonic evolution are highly important in terms of global climate change and geodynamic study. However, a comprehensive understanding of the SHF distribution across most regions of the Tibetan Plateau is limited due to sparse measurement data. To surmount this limitation, a spatially intelligent approach has been developed: The geographically neural network weighted regression with enhanced interpretability (EI-GNNWR). This method integrates spatial heterogeneity and nonlinear interactions between geophysical and geological factors to predict the SHF distribution across the Tibetan Plateau. In this study, the EI-GNNWR model is used to accurately predict SHF across the entire region. After evaluating the effectiveness and interpretability of the EI-GNNWR model, our results demonstrate that medium to high SHF values are predominantly concentrated in the southern, northeastern, and southeastern sectors of the Tibetan Plateau. These observations suggest that the formation of zones with high SHF values may be strongly influenced by the Moho depth, ridges, topography, and average curvature of satellite gravity gradients. Especially, higher SHF values may indicate more profound geodynamic activities such as collisional orogeny, shear deformation zones, or lithospheric extension. These findings offer novel insights into the spatial patterns of SHF and deepen our understanding of the geothermal formation mechanisms driven by underlying tectonic activities.

It remains uncertain whether a stagnant slab in the mantle transition zone can affect the asthenospheric mantle beyond its leading edge. To address this question, we investigated Cenozoic alkaline basalts from the Dariganga volcanic field (DVF) in southeastern Mongolia. The DVF is located west of North–South Gravity Lineament (NSGL) in Eastern China, which is spatially coincident with the seismically detected stagnant Pacific slab front. Basalts from the DVF consist of nephelinite, basanite and alkali olivine basalt. These rocks have relatively high Nb/U (average = 58) and Nb/La (>1) ratios and radiogenic Nd–Hf isotopic compositions. They also have high Ca/Al (0.60–1.13), Zn/Fe^T (13.5–16.5), and FeO/MnO (77–112) ratios as well as low δ²⁶Mg (−0.42‰ to −0.26‰) values, reflecting an asthenospheric mantle source modified by carbonated eclogite-derived melts. Pb–Nd–Hf isotope characteristics indicate that the carbonated eclogite-derived melts likely originated from the stagnant Pacific slab. Although Cenozoic basalts from both the east of the NSGL (ENSGL) and DVF domains exhibit light δ²⁶Mg values, basalts from the ENSGL nevertheless have lower δ²⁶Mg values than those in the DVF domain. This suggests a gradual westward decline in the amount of carbonated melts/fluids derived from the stagnant Pacific slab. This variation trend, combined with a more fertile and oxidized asthenospheric mantle toward the ENSGL, indicates that the stagnant slab has affected the mantle and created a compositional aureole beyond its leading edge, which substantially contributed to the formation of the alkaline basalts in the DVF.

The Neoproterozoic carbonate rocks of the Araras Group (Amazon Craton) and the Sete-Lagoas and Salitre Formations (São Francisco Craton) share a statistically indistinguishable single-polarity (reversed) characteristic direction. This direction is associated with paleomagnetic poles that do not align with the expected directions for primary detrital remanence. We employ a combination of classical rock magnetic properties and micro imaging/chemical analysis (in thin sections) using synchrotron radiation to examine these remagnetized carbonate rocks. Magnetic data indicate that most samples lack the anomalous hysteresis properties typically associated with carbonate remagnetization (except for distorted loops). Through a combination of Scanning Electron Microscopy with Energy Dispersive X-ray Spectroscopy (SEM-EDS), X-ray Fluorescence (XRF), and X-ray Absorption Spectroscopy (XAS), we identified subhedral/anhedral magnetite, or spherical grains with a core-shell structure of magnetite surrounded by maghemite. These grains are within the pseudo-single domain size range, as do most of the iron sulfides, and are spatially associated with potassium-bearing aluminosilicates. While fluid percolation and organic matter maturation play a role, smectite-illitization appears to be crucial for the growth of these phases. X-ray diffraction analysis, in addition, identifies these silicates as predominantly highly crystalline illite, suggesting exposure to epizone temperatures. These temperatures were likely reached during the final stages of the Gondwana assembly (Cambrian), but remanence was only locked in afterward, in successive cooling events during the Early Middle Ordovician. This is supported by the carbonates' paleomagnetic pole positions compared to Gondwana's apparent polar wander path, and the absence of reversals, contrasting with the high reversal frequency of the Late Ediacaran/Cambrian.

On continental margins, sediments cause significant and spatially variable delays in seismic phase arrival times. The strong impedance contrast of the sediment-bedrock interface causes P-wave splitting that is clearly seen on distributed acoustic sensing recordings of earthquakes, resulting in additional phase arrivals that must be picked separately. We introduce sediment corrections to correctly account for those additional phases in the hypocenter localization procedure. Conceptually, the sediment correction method differs from the commonly-used station corrections; instead of introducing a mathematically optimal constant time delay for each station and each phase, the corrections are derived from a physical, first-order modeling of the wave propagation in the sediments. To calibrate the sediment corrections, a two-step procedure is adopted: (a) the delay between the P-phase and the converted Ps-phase is taken as a proxy of the sediment thickness; (b) the P- and S-wave speeds are determined through inversion. We show that sediment corrections are able to account for most of the observed bias while considerably reducing the number of free parameters compared to classical station correction. Moreover, the observed local delays are almost fully explained by the presence of the sedimentary layer, rather than by the 3D velocity variations of the bedrock. We retrieve $��v_P�$ and $��v_S�$ values that are compatible with values commonly found for sediments. Given the simplicity and physical foundation of the proposed method, we recommend the use of sediment corrections over station corrections whenever significant P-wave splitting can be observed.

Earthquakes can produce rock damage, poroelastic deformation, and ground shaking that modify fault zone hydrogeologic properties. Coseismic and postseismic hydrologic response to the ruptured fault can serve as constraints on hydrogeologic property changes. Here, we document fluid pressure responses to the 2018 M6.3 Hualien, Taiwan earthquake and model the postseismic fault zone hydrology inferred from very-near-fault data. Two groundwater wells located ∼180–250 m from the fault damage zone experienced 10–15 m of groundwater level decline followed by a prolonged (>6 months) recovery. Poroelastic models indicate that strain dilation in the fault's hanging wall can produce water level reductions of several meters. However, the model cannot explain groundwater level change in the footwall nor the delayed postseismic recovery, suggesting fault zone damage played a primary role in both the coseismic and postseismic water level reductions. Fluid flow models incorporating the effects of coseismic fault damage on the temporal evolution of hydrologic fault properties show enhanced hydraulic anisotropy after the earthquake. The best-fit models show that while both vertical hydraulic conductivity and specific storage likely increased within the fault zone, the horizontal hydraulic conductivity is low, suggesting the fault zone behaves as a hydraulic barrier to cross-fault flow with modeled diffusivities as low as ∼10⁻³ m²/s. High-fidelity hydrologic measurements in the very-near-field of fault zones (e.g., within a few hundred meters) may be a useful tool to constrain the spatial and temporal evolution of fault zone properties before, during, and after rupture.

C-band Interferometric Synthetic Aperture Radar (InSAR) data are widely used to map coseismic deformation. However, phase unwrapping errors are commonly distributed near faults owing to decorrelation and steep phase gradients from short radar wavelengths. Here, we propose an improved SNAPHU phase-unwrapping algorithm that considers the prior information of the range offset gradients (P-SNAPHU) to overcome the constraints imposed by the phase continuity assumption. P-SNAPHU exploits median filtering of homogeneous pixels for initial denoising of range offset and then refines range offset gradients divisionally through saliency extraction. The derived gradients are used to estimate the expected values of the cost functions for the low-coherence fringes. The synthetic experiments show significant improvements in the phase-unwrapping accuracy of the P-SNAPHU method compared with classical unwrapping methods. We apply the P-SNAPHU method to unwrap Sentinel-1 coseismic interferograms of three large (Mw > 6.5) strike-slip earthquake events that the existing classical methods could not successfully unwrap. In the comparison of the unwrapped interferograms with the external global navigation satellite system (GNSS) displacements and those from the classical methods, we find that P-SNAPHU significantly reduces the phase unwrapping errors with the mean absolute error of 7.2, 2.3, and 1.8 cm for the 2023 Kahramanmaraş earthquake doublet, the 2016 Kumamoto earthquake, and the 2019 Ridgecrest earthquakes, respectively. Based on the unwrapped results derived from P-SNAPHU, an estimate is made regarding the shallow slip deficit of the 2023 Kahramanmaraş earthquake doublet, which is approximately 7%. Therefore, P-SNAPHU is useful for developing and applying C-band InSAR data for large earthquakes and volcanic activity.

Large earthquakes rupture faults over hundreds of kilometers within minutes. Finite-fault models image these processes and provide observational constraints for understanding earthquake physics. However, finite-fault inversions are subject to non-uniqueness and uncertainties. The diverse range of published models for the well-recorded 2011 $��M_w�$ 9.0 Tohoku-Oki earthquake illustrates this challenge, and its rupture process remains under debate. Here, we comprehensively compare 32 published finite-fault models of the Tohoku-Oki earthquake. We aim to identify the most coherent slip features of the Tohoku-Oki earthquake from these slip models and develop a new method for quantitatively analyzing their variations. We find that the models correlate poorly at 1-km subfault size, irrespective of the data type. In contrast, model agreement improves significantly with increasing subfault sizes, consistently showing that the largest slip occurs up-dip of the hypocenter near the trench. We use the set of models to test the sensitivity of available teleseismic, regional seismic, and geodetic observations. For the large Tohoku-Oki earthquake, we find that the analyzed finite-fault models are less sensitive to slip features smaller than 64 km. When we use the models to compute synthetic seafloor deformation, we observe strong variations in the synthetics, suggesting their sensitivity to small-scale slip features. Our newly developed approach offers a quantitative framework to identify common features in distinct finite-fault slip models and to analyze their robustness using regional and global geophysical observations for megathrust earthquakes. Our results indicate that dense offshore instrumentation is critical for resolving the rupture complexities of megathrust earthquakes.

The extremely oblique Indo-Burma subduction zone exhibits dextral strike-slip faulting along the Sagaing, Kabaw, and Churachandpur-Mao Faults as well as east-west shortening between the Sagaing Fault and Bengal Basin. Through regional stress analysis, considering areas from central Tibet, around the eastern Himalaya Syntaxis, to Burma, it has been determined that the principal compressive stress directions align with the principal strain rates. The northeast-southwest oriented compressive stress direction from the western Shan Plateau continues into Burma. Notably, P axes align with the topographic gradients, and T axes are sub-parallel to the topographic contours in the Shan Plateau region south of 27°N. These stress patterns are consistent with a gravitational potential energy induced crustal and mantle flow. The alignment of the fast shear wave with the maximum strain rate and the colinear NW-SE to E-W fast direction of the SKS wave and T axis determined from focal mechanisms in the Shan Plateau suggest that the mantle lithosphere deforms in concert with the crust. We suggest crust and mantle flow south of the Red River Fault has resulted in widening of the lithosphere in the Shan Plateau in an east-west direction. Therefore, the Sagaing Fault has bowed approximately 50–100 km westward if we assume that the Sagaing Fault was originally straight. Our results of regional stress inversion are consistent with late Miocene to present E-W shortening in the Indo-Burma subduction zone resulting from the release of gravitational potential energy from the central Tibetan Plateau.

Despite significant study, when and how plate tectonics initiated on Earth remains contentious. Geologic evidence from some of Earth's earliest cratons has been interpreted as reflecting the formation of initial continental blocks by non-subduction processes, which then trigger subduction initiation at their margins. Numerical models of mantle convection with a plastic yield stress rheology have shown this scenario is plausible. However, whether continents can trigger subduction initiation has not been tested with other rheologies. We, therefore, use numerical models of mantle convection with an imposed continental block to test whether continents facilitate subduction initiation with a grain-damage mechanism, where weak shear zones form by grain size reduction. Our results show that continents modestly enhance stresses in the lithosphere, but not enough to significantly impact lithospheric damage or subduction initiation: continents have minimal influence on lithospheric damage or plate speed, nor does subduction preferentially initiate at the continental margin. A new regime diagram that includes continental blocks shows only a small shift in the boundary between the mobile-lid and stagnant-lid regimes when continents are added. However, as we do find that stresses are modestly enhanced at the continental margin in our models, we develop a scaling law for this stress enhancement to more fully test whether continents could trigger subduction initiation on early Earth. We find that lithospheric stresses supplied by continents are not sufficient to initiate subduction on the early Earth on their own with grain-damage rheology; instead, additional factors would be required.

Plagioclase feldspar is a major mineral in mafic crustal rocks. To better understand the deformation mechanism of plagioclase feldspar during frictional faulting, we conducted shearing experiments on simulated plagioclase gouge in a wide range of effective normal stress of 100–300 MPa, pore-water pressure of 30–100 MPa, and temperatures ranging from 100°C to 600°C. The coefficient of friction is found to range from 0.65 to 0.74 across the entire temperature range, showing no significant thermal weakening process. Except for a case at 200°C with an effective normal stress of 300 MPa, the frictional sliding is velocity weakening over the whole temperature range, showing a steady-state rate dependence (a−b) ranging from −0.5 × 10⁻³ to −8.6 × 10⁻³. This property facilitates nucleation of unstable slips in frictional faulting. Above 200°C, the direct rate effect parameter (a) and the evolution effect parameter (b) of friction increase with temperature up to a threshold of 400°C or 500°C, depending on the effective normal stress. This thermal enhancement suggests thermally activated creep at contact junctions governed by intergranular pressure solution, as evidenced by microstructural signatures indicating the prevalence of very fine precipitates formed at the surfaces of gouge particles as a result of pressure solution. In frictional sliding of plagioclase, a low effective normal stress of 100 MPa corresponds to a higher degree of velocity weakening and tends to facilitate seismic slip rather than slow slips, whereas the high effective normal stress of 300 MPa corresponds to a minor velocity weakening which may cause slow-slip events in faults of limited size.