Journal of Geophysical Research: Solid Earth最新文献

Deep-origin carbonatite melts are considered to be the products of partial-melting of the oceanic crust in the subduction zones. In this study, we conducted electrical conductivity (EC) measurements on two samples, the composition of which resemble the partial-melting products atop the 410-km discontinuity and in the lower part of the transition zone. The EC of carbonatite melts was investigated using impedance spectroscopy combined with a multi-anvil press up to 20 GPa. Pressure has a great effect on the EC of the carbonatite melts. While the EC dropped overall by 0.6 log unit from 3 to 20 GPa for varying compositions, the pressure effect becomes weaker above 10 GPa. The Hashin-Shtrikman mixing model indicates that melt fraction of 0–0.3 vol% is necessary to account for the EC atop the 410-km discontinuity beneath NE China, north Philippine Sea, north Pacific, and Australian craton. However, this value soars to 1–4.5 vol% for the lower part of the transition zone in the same regions, and further increases to 3.7–7.3 vol% for cold subduction regions if the slab surface temperature is 300 K lower. The difference in the needed melt fraction at different depths implies that the magnitude of partial melting is much larger in the lower part of the mantle transition zone, and it is thus likely to be the main barrier to the recycled carbonates towards the deep interior.

Paleomagnetic data are usually retrieved by subjecting bulk samples, for example lavas, to laboratory measurement protocols. In many instances, the data related to these protocols yield uninterpretable results caused by the presence of particles with adverse magnetic properties that blur the signal of the reliable magnetic particles. With Micromagnetic Tomography (MMT) we focus on identifying the signal of particles with reliable properties. Their individual magnetic moments are computed by scanning the surface of a $��\sim �$3 $��{\text{mm}}^2�$ thin section with a quantum diamond microscope (QDM) and locating the magnetic recorders with computed tomography. Currently, the largest portion of all resolved magnetic moments is discarded due to numerical instability, making it difficult to obtain statistically relevant paleointensities and paleodirections based on the remaining magnetic moments. We improve the number of reliable magnetic moments from MMT experiments by making a QDM scan of both sides of the sample. Here, we conduct a combined numerical and empirical study to investigate the benefits and difficulties of adding this double-sided scanning (DSS) protocol to MMT. By investigating the theoretical gain of DSS for varying sample thicknesses, we show that DSS returns twice more numerically stable magnetic moments compared to single sided scanning for a sample thickness of 60 $��\mu �$m. By overcoming practical difficulties related to sample preparation and scanning, DSS will provide a significant boost in retrieved stable magnetic moments.

At the northern Hikurangi margin, Aotearoa New Zealand, slow slip events (SSEs) recur every 6–24 months to $��\sim �$30 km depth. Although shallow SSEs (0–10 km) are well-studied offshore, the deeper portion (10–30 km) remains poorly understood, limiting insight into SSE initiation. Here we investigate this deeper region and examine relationships between newly resolved SSEs and seismicity. Using time-dependent inversions, we resolve two small SSEs ($��M_W�$ 6.2 and 6.4), including one that extends from 15 to 30 km depth. Using data from a dense onshore seismograph network deployed directly above this deeper portion from December 2017 to October 2018, we construct a catalog of 3,071 high-quality earthquakes with hypocentral uncertainties $��\le �$5 km, located using a 3-D velocity model and a new 1-D model. Earthquake magnitudes range from −0.84 to 4.40, with a completeness magnitude of 1.7 and a b-value of 1.06. Focal mechanisms reveal numerous normal-faulting earthquakes, including some within the slab mantle. Vertically-aligned seismicity and normal-faulting earthquakes outline pathways linking the slab mantle to surface seeps of mantle-derived fluids. We infer that normal faults form due to slab bending and localized uplift of subducting seamounts, which roughen the plate interface, damage the upper plate, and promote fluid migration. Landward of $��\sim �$100 km from the trench, both surface seeps and normal-faulting mechanisms cease, coinciding with the downdip limit of shallow SSEs. Together, these results suggest that the Hikurangi margin's rough subducting plate interface exerts strong control on forearc dewatering and SSE genesis.

Induced shear failure is key for enhancing hot dry rock (HDR) resource exploitation, aiming to creating an extensive fracture network. Although the macroscopic shear behavior of HDR has been extensively investigated, its microscopic shear failure mechanisms remain unclear. In this study, microscale mode II shear fracture experiments were performed for the first time under various thermal cycling. Micro-scale double-edge notched cube specimens were fabricated from primary minerals and interfaces using micro-machining and subjected to in situ shear tests under a scanning electron microscope. The microscopic shear failure mechanisms and fracture parameters of the minerals and interfaces were investigated. The results showed that multiple thermal cycles reduced macroscopic shear strength by initiating thermal cracks rather than by reducing the strength of the microscale minerals. All three minerals exhibited L-shaped crack propagation below 300°C, with shear initiation and tensile failure. Biotite failed progressively, whereas feldspar and quartz failed catastrophically. High temperatures and multiple thermal cycles caused thermal voids and complex crack paths in feldspar and quartz, whereas biotite exhibited fiber-like plastic slip bands without thermal cracking. The orientation and strength of the mineral interfaces affected crack deflection and branching. Energy was dissipated by interlayer plastic slip in biotite and by micro-crack friction and slip in quartz and feldspar. The microscopic mode II fracture toughness and critical energy release rate were 0.5–3.3 MPa·m^0.5 and 0.01–0.11 kJ/m², respectively. This research provides novel insights into the microscale shear failure of HDR and a critical micromechanical basis for multiscale fracture modeling and macroscopic shear failure analysis.

Fluid transport properties at the base of the seismogenic zone exert a critical control on fault strength, slip behavior, and fluid circulation. However, quantitative constraints on permeability in deep fault rocks remain limited. We present new laboratory measurements of permeability, porosity, and specific storage on cataclasite- and pseudotachylyte-bearing mylonitic rocks along the Red River Fault (RRF), China. Experiments conducted at effective pressures up to 165 MPa reveal systematically low permeabilities, with mylonitized cataclasites and pseudotachylyte-bearing rocks exhibiting the lowest values (10⁻²²–10⁻²¹ m²), while mylonites display relatively higher permeabilities, up to 10⁻¹⁹ m². A key finding is the pronounced permeability anisotropy, where permeability parallel to foliation is up to two orders of magnitude greater than perpendicular values. This anisotropy reflects the microstructural alignment of phyllosilicate minerals and cavitation bands, which provides interconnected flow pathways along foliation while impeding cross-foliation transport. The hydraulic architecture of the RRF at the base of the seismogenic zone is thus characterized by overall low permeabilities with fluid flow facilitated along mylonitic foliation. Such fabric-controlled anisotropy persists even under mid-crustal pressure conditions, indicating that fault zones at the base of seismogenic depths can retain directional fluid pathways despite overall low permeabilities. Our results provide critical constraints on the hydraulic architecture of the RRF and offer broader insights into the role of anisotropy in controlling fluid flow and deformation at the base of the seismogenic zone.

The Okavango Rift Zone (ORZ) is an incipient continental rift in Botswana at the terminus of the Southwestern Branch of the East African Rift System. The lack of syn-rift magmatism and tectonic processes overprinting pre-rift structures provide an opportunity to investigate incipient-stage rift processes and the role of pre-existing structures in rift initiation and strain localization. We present SEISORZ, a ∼450-km-long wide-angle seismic transect across the ORZ and neighboring tectonic terranes. A 2.5-D V_P tomographic inversion reveals crustal thinning within a ∼130-km-wide section of the Damara Belt hosting the ORZ where Moho depth is 38.7 ± 3.4 km, shallower than in other Damara Belt terranes (46.3 ± 1.4 km) and the Kalahari Craton (45.6 ± 2.0 km). Mantle V_P is consistent with ultramafic lithologies without evidence for metasomatism, partial melt, or elevated temperatures. Crustal V_P is variable but consistent with geological information and with lower-crustal mafic lithologies. However, beneath the rifting region, the model shows low crustal velocities (ΔV_P = −0.26 ± 0.05 km/s) that we interpret as damage from rift-related faulting and deformation, and to a lesser extent elevated temperatures possibly from excess radiogenic heat production. Upper crustal heterogeneity correlates with known and newly detected intra-rift faults, suggesting that pre-existing structures promoted strain localization and establishment of the rift border fault system. Collectively, all these factors point to a rheologically weak section in the Ghanzi-Chobe zone which is more susceptible to deformation in response to far-field stresses than neighboring terranes, explaining why incipient rifting is localizing there and not across any other of the terranes that compose the Damara Belt.

Accurate characterization of fracture geometry and reservoir structure is essential for the successful design and development of Enhanced Geothermal Systems (EGS). Conventional surface seismic imaging often lacks the resolution to delineate hydraulic fractures at depth due to strong attenuation and limited source frequency. This study presents high-resolution imaging of the Utah FORGE site using Distributed Acoustic Sensing (DAS) recorded microseismic data during the [16A(78)-32] injection activities. We developed an imaging technique that leverages microseismic events as imaging sources, applies prestack Kirchhoff migration to each individual source, then stacks hundreds of sources to generate a 3D reflectivity volume. The imaging workflow produces a high-resolution map of the regional granitoid contact and, more importantly, reveals internal structures within the heart of the geothermal reservoir that have not been previously described. By correlating well-log data and geological evidence, we identify a low-angle interface located just below and nearly parallel to the granitoid contact. Key findings also reveal two natural fractures near the stimulation zone, visible prior to stimulation, which may accommodate the injected fluid and affect the hydraulic fracturing efficiency. Those internal structures are difficult to observe by typical surface sources since the regional granite-alluvium interface is strong and not easily penetrated by seismic waves. Time-lapse imaging of the hydraulic fracture is conducted and integrated with low-frequency DAS to construct a more comprehensive fracture geometry. In conclusion, the 3D fracture volume produced by DAS microseismic reflection imaging deepens our understanding of geothermal reservoir dynamics, potentially enhancing geothermal characterization and exploitation strategies.

The 15 January 2022 submarine volcanic eruption of Hunga Tonga-Hunga Ha'apai released immense energy throughout the ocean, solid Earth, and atmosphere. We analyze mid-oceanic column acoustic pressure recordings from 24 freely drifting Mobile Earthquake Recorder in Marine Areas by Independent Divers sensors, and from 11 moored hydrophones in the International Monitoring System. We focus on the pulsed hydroacoustic phase which propagated horizontally through the ocean as a 30-min T wave with energy around 2.5–10 Hz. The records show high correlation between some receivers, significant variation among others, and varying amplitudes that cannot be explained by distance alone. We investigate the origin of this heterogeneity via the influence of bathymetric features that may block, or occlude, T-wave propagation, affecting both shape and amplitude of the records received. We count the number of seafloor obstacles within the horizontal plane of the first (ray-theoretical) Fresnel zone at a depth of 1,350 m, where the fundamental-mode T-wave eigenfunction is maximal. Adjusted for geometric spreading, the cross-correlations and sound pressure level differences between receivers systematically relate to differences in occlusion count. Our model of signal loss due to seafloor interactions predicts a 5.6 dB reduction in sound pressure level per logarithm of occlusion count, explaining 88% of the T-wave sound pressure variance across the ocean. Source characterization requires adequate path models. Our findings describe how to correct signal amplitudes for seafloor roughness. This is important for constraining volcanic or explosive yield estimates and earthquake magnitudes, and useful to model detectability through various oceanic corridors when designing hydroacoustic monitoring networks of the future.

Hydrologic observations and experimental studies indicate that inelastic dilation from coseismic fault damage can cause substantial pore pressure reduction, yet most near-fault hydromechanical models ignore such inelastic effects. Here, we present a 3-D groundwater flow model incorporating the effects of inelastic dilation based on an earthquake dynamic rupture model with inelastic off-fault deformation, both on pore pressure and permeability enhancement. Our results show that inelastic dilation causes mostly notable depressurization within ∼1 km off the fault at shallow depths (<3 km). We found agreement between our model predictions and recent field observations, namely that both sides of the fault can experience large-magnitude (∼tens of meters) water level drawdowns. For comparison, simulations considering only elastic strain produced smaller water level changes (∼several meters) and contrasting signs of water level change on either side of the fault. The models show that inelastic dilation is a mechanism for coseismic fault depressurization at shallow depths. While the inelastic dilation is a localized phenomenon which is most pronounced in the fault zone, the pressure gradients produced in the coseismic phase have a broader effect, increasing fluid migration back into the fault zone in the postseismic phase. We suggest field hydrologic measurements in the very-near-field (<1 km) of active faults could capture damage-related pore pressure signals produced by inelastic dilation, helping improve our understanding of fault mechanics and groundwater management near active faults.