Journal of Geophysical Research: Solid Earth最新文献

First-order reversal curve (FORC) diagrams are an important tool for assessing the domain state and anisotropy type of magnetic particles, as well as for detecting magnetostatic interactions among particles, in paleoclimatic, geomagnetic, tectonic, and planetary studies. We present here FORC diagrams for diverse natural monoclinic 4C pyrrhotite (Fe₇S₈) samples, including sieved particle size fractions. Experimental FORC distributions for natural pyrrhotite have a dominant asymmetric “kidney shaped” feature for fine particles in the stable single domain (SD) size range. As particles coarsen to the multi-domain state, FORC distributions diverge vertically at low coercivities. Vertical spreading in FORC distributions is also an intrinsic response of magnetic particle systems with multiaxial anisotropy even for magnetostatically noninteracting SD particles. The observed kidney shaped FORC distributions are attributed to twin domain and magnetic moment pinning along easy directions that follow the hexagonal parent structure to produce an apparent triaxial magnetocrystalline anisotropy signal. Similar FORC distributions have been reported for pyrrhotite, hematite, and smythite, which all have basal plane triaxial anisotropy. Central ridge-type signatures, which are typical of noninteracting uniaxial SD particle assemblages, have been reported for some pyrrhotite samples, but are not documented here. Our results explain FORC features for pyrrhotite and provide a catalog for comparison with other studies.

Monitoring disturbances in the subsurface medium of Antarctic glaciers and their connection to environmental changes is crucial for addressing sea level rise due to glacier melting. This study utilizes ambient noise data collected by dense seismic arrays deployed near Dalk Glacier in East Antarctica during the 36th Chinese National Antarctic Research Expedition. Using coda wave interferometry, we measured in situ nonlinear elasticity (relative velocity changes, dv/v) and observed hysteresis loop characteristics consistent with laboratory experiments. Our results demonstrate delayed dv/v responses to environmental forcing, with short-term variations independent of atmospheric pressure. Semi-diurnal dv/v variations are controlled by tidal strain, humidity, and ice melt dynamics, while sensitivity to melt rate exceeds the response to total melt volume. This cost-effective, high-resolution monitoring technique complements existing methods for monitoring mass changes in the Antarctic ice sheet, aiding in the detection and understanding of low-amplitude precursors to the systemic imbalances of glaciers.

Lahars are among the most frequent hazards associated with Volcán de Fuego, Guatemala. Despite their recurrence, early detection and automated alerts remain challenging since they often rely on manual monitoring and sparse visual confirmation. Yet, we can harness the high number of flows triggered every rainy season to characterize their seismic signatures and quantify their size and behavior. For this, we used seismic stations located along two active lahar channels on Fuego where this characterization describes a somewhat stable long-term flow behavior. This work revealed more varied short-term behavior characterized by increasing seismic activity in the time domain and a shift toward lower frequencies as these flows propagate downstream. Building on this characterization, we implemented K-nearest neighbor (KNN) based detectors using seismic signal attributes describing samples of the data in the time and frequency domains, as well as statistical functions of these samples. We trained generalized and station-specific detectors that achieved high accuracy for detecting moderate-to-large flows with lower performance for smaller or ambiguous events. We found that root mean square amplitude, a proxy for flow size, appears to control detector performance more than other signal features. The detector is computationally efficient and, in the case of Fuego, did not require additional instrumentation. This framework presents a portable solution for enhancing automated lahar detection while minimizing the use of location-specific parameters required by other methods.

Volcano deformation measured through Interferometric Synthetic Aperture Radar (InSAR) is ideal for volcano monitoring in many regions due to its global coverage, characteristic spatio-temporal patterns, and modeling insights. Routinely acquired and processed Sentinel-1 InSAR datacubes provide the first opportunity to systematically catalog, model and compare volcano deformation globally. Here, we present a framework (GBIS-BULK) to systematically pre-process and model volcano deformation signals, designed to be applied to routinely processed InSAR data sets. This requires a robust (semi-) automated approach to estimate signal locations and footprints for effective pre-processing and modeling. Our approach combines (a) filtering and clustering to locate the signal center; (b) noise reduction using Independent Component Analysis (ICA); and (c) image classification using Otsu thresholding to delimit the signal footprint. We invert for the best-fit point source model using constraints from existing global volcano deformation catalogs. First, we examine the influence of downsampling schemes, image noise and coherence using synthetic interferograms, showing nested-uniform downsampling is more suited to automated processing than quadtree methods which typically require manual tuning. Then, we validate the approach using Sentinel-1 deformation images from the East African Rift System (EARS). The pre-processing steps reasonably locate the signal at 15/16 of the EARS volcanoes, and the signal footprint at 14/16. ICA reduces or approximately maintains the image RMS in all cases. Our systematic point source estimates showed consistency when directly compared with previous (bespoke) modeling studies. This approach has the potential to be integrated with existing toolkits for routinely processing and analyzing Sentinel-1 InSAR data and hence applied globally.

The geology of New Zealand has been shaped by tectonic plate interactions driven by mantle convection over the past 60 million years, but the effects of these interactions on the transition to the lower mantle are not yet well understood. We analyze 10 years of teleseismic $��P�$-wave receiver functions using common conversion point stacking to investigate mantle transition zone discontinuities. The resulting topography of the 410-km and 660-km discontinuities, smoothed using kriging interpolation, reveals localized thermal anomalies. We observe more than 10 km of thinning in the mantle transition zone beneath central North Island coincident with the Hikurangi slab, accompanied by a significantly thickened and hydrous melt-rich layer above the 410-km discontinuity. In northern South Island, the 410-km discontinuity is uplifted by approximately 15 km, likely reflecting subducted materials from the oblique Hikurangi slab material reaching mantle transition zone depths. These observations are consistent with patterns of seismicity and seismic velocity anomalies from tomographic models. Additionally, we identify significant thinning of the mantle transition zone beneath both the Northland region ($��\sim �$10 km) and the Great South Basin ($��\sim �$15 km), indicating the influence of potential local thermal upwellings. The different slab polarities and transpressional boundary may drive lateral mantle flow, shaping the complex transition zone topography beneath New Zealand.

Fluids released from subducting hydrated rocks influence volcanism, tectonics, and geochemical cycling, but the mechanisms of fluid escape in subduction zones remain poorly understood. We address this issue by investigating the Erro-Tobbio meta-serpentinites (ET-MS), Italy, exhumed serpentinite rocks that preserve extensive dehydration vein networks formed by the porosity-generating breakdown of antigorite and brucite. We characterized the structure and morphology of these self-organized vein networks and evaluated their hydrodynamic properties using a novel approach. Specifically, we combined X-ray tomography and drone imagery with generative machine learning, electron microscopy, and equilibrium thermodynamics to model and analyze fluid pathways in the ET-MS. In both natural and simulated samples, these dehydration vein networks act as efficient drainage systems, enabling rapid fluid percolation even at porosities below 1%. The maximum network permeability is $��\approx �1�0^{�-�15�}�{��m�}^2�$, several orders of magnitude higher than that of intact serpentinite. Fe-rich olivine and monticellite occur alongside relict brucite and magnetite in these veins. This assemblage indicates that the high permeability arises from porosity localized along brucite- and magnetite-rich veins, where infiltration of reducing fluids enhanced dehydration reactions. These findings demonstrate that serpentinite dehydration in subduction zones can produce flow-optimized vein structures that efficiently channel fluids at low porosity, potentially influencing fluid migration on local to regional scales before widespread dehydration occurs.

This study investigates whether seismicity in the New Madrid Seismic Zone (NMSZ), specifically the Axial Fault, is predominantly influenced by fluids or fault locking. Previous resistivity studies in the region were restricted by their focus, MT station spacing, and equipment bandwidth, which limited the resolution of resistivity structures near fault zones. We conducted a comprehensive investigation using broadband magnetotelluric (MT) soundings from December 2021 to March 2023. Data were collected along five profiles spanning frequencies from 0.00005 to 10,000 Hz. Four shallow-focus profiles were located near Steele and Caruthersville in the Missouri Bootheel region, while a deeper cross-section extended from Obion, TN to Wardell, MO, reaching a depth of 80 km and crossing the Reelfoot Rift's Axial Fault. Our findings indicate that earthquakes cluster within a highly resistive zone (1,000–10,000 Ω-m), suggesting a fault-locking mechanism in the brittle zone because they coincide with low velocity anomalies from previous studies. The profiles usually have a conductive anomaly on the SE side of the fault at a depth of 2–30 km. That conductive anomaly may be interpreted as a weaker, more ductile zone adjacent to the stronger brittle zone associated with the fault. These results suggest that both fault locking and fluid presence significantly influence NMSZ seismicity, with their effects varying by depth and location.

The Appalachian-Caledonian orogen was built during the Paleozoic by accretion of peri-Gondwanan terranes onto Laurentia, culminating in the formation of Pangea. During the Mesozoic, Pangea broke apart, displacing one section of the belt to eastern North America and another to northwestern Europe. These areas share aspects of their tectonic history but have been shaped differently by later Paleozoic orogenesis and Mesozoic rifting; therefore, comparisons between these regions offer an opportunity to understand which processes have been responsible for shaping their present-day crustal structure. This study compares the crustal structure across the Laurentian and peri-Gondwanan sutures in these regions and explores how it has been shaped by their tectonic histories. We use receiver functions with harmonic decomposition to analyze the geometry of Laurentia, Ganderian and Avalonian crust beneath Ireland and Britain and compare them with New England, northeastern USA. The Laurentian crustal thickness beneath Ireland and Britain ranges from ∼26 to 32 km, whereas that of the peri-Gondwanan terranes varies from ∼32 to 38 km. Our analysis also provides insight into dipping interfaces and anisotropy near the Moho, which vary considerably across the study area. In contrast to our findings in Ireland and Britain, beneath New England Laurentian crust is significantly thicker (∼44 km) than accreted terrane crust (∼32 km). We hypothesize that Mesozoic rifting led to significant thinning of Laurentian crust beneath Ireland and Britain, and that regionally specific orogenic processes during the middle and late Paleozoic controlled the evolution of accreted terrane crust differently in these areas.

The Greater Alpine crust provides a natural laboratory for investigating tectonic and geodynamic processes owing to its strong structural and lithological heterogeneity. A key challenge is constraining its thermal and compositional properties, given the limited direct observations and the uncertainties of existing models. We analyze two years of seismic ambient noise recorded at about 700 broadband seismic stations, and eight years of teleseismic earthquakes recorded at approximately 400 broadband stations. Using ambient noise tomography and receiver functions, we derive the Vs of the crust, the average Vp/Vs ratio, and a new Moho depth map for the Greater Alpine region. Moho depths range from 15 to 55 km, and Vp/Vs ratios vary from <1.65 in the Variscan domain to >1.8 in the Apennines, Dinarides and sedimentary basins. Thermodynamic modeling translates these seismic results into quantitative estimates of silica content and linear thermal gradients. We find that the Variscan crust is relatively cold (<20°C/km) and silica-rich (>62 wt% $��S�i�O_2�$), in contrast with Alpine–Apenninic domains that show elevated thermal gradients (>25°C/km) and more mafic compositions (<60 wt% $��S�i�O_2�$). However, elastic velocities predicted by mineral physics systematically exceed observed seismic velocities, reflecting effects of sediments, porosity, anelastic relaxation, and non-equilibrium processes not captured in thermodynamic equilibrium models. We apply empirical corrections to address these discrepancies, emphasizing caution when interpreting seismic velocities from mineral physics models. These quantitative constraints refine the thermal and chemical distinction between stable Paleozoic lithosphere and actively deforming orogens in the Greater Alpine crust.