Journal of Geophysical Research: Solid Earth最新文献

The Drake Passage is characterized by strong ocean currents barely allowing the deposition of fine grained sediments. Only in smaller basins protected from these currents sediments are able to settle more or less continuously. Two sediment cores from within the Drake Passage were subjected to magnetostratigraphic analyses. In one core inclinations are too steep while they are too shallow in the other one. Tentatively, directions of both cores were slightly tilted so that the maximum of the inclination distribution aligns with the direction of a geocentric axial dipole. Inclination variations then correlate fairly well, while declinations still show only little congruence. This is interpreted as the result of locally varying bottom currents partly biasing the remanence acquisition processes. Nevertheless, due to the high latitude of the coring site at 58°S, the field vector is mostly dominated by inclination and intensity variations. Directional variations during the documented Mono Lake (34.5 ka) and Laschamps (41.0 ka) geomagnetic excursions are only slightly changed by the applied tilt-correction and afterward correlate very well from core to core. The Mono Lake excursion is characterized by shallow inclinations only, indicating a non-axial dipolar field geometry. The field vector during the Laschamps excursion reaches a fully reversed direction. Both excursions are associated with clear minima in paleointensity. During the Laschamps excursion even a slight field recovery can be observed during the reversed phase of the field vector. Both excursions in Drake Passage sediments are terminated fairly abruptly followed by a more or less steep increase in paleointensity.

We present a novel finite fault inversion algorithm that combines W-phase finite fault inversion with Image Deconvolution Back-Projection (IDBP) for the determination of coseismic slip models following large earthquakes. This integrated algorithm leverages the strengths of both methods, enabling rapid determination of moment tensor, slip distribution, and centroid location. The application of this integrated algorithm to the analysis of the 2015/04/25 Mw 7.8 Nepal and the 2013/01/05 Mw 7.5 Craig Alaska earthquakes yielded results closely aligned with detailed post-earthquake studies, highlighting the algorithm's accuracy and reliability. By overcoming inherent limitations of individual methods, it provides a comprehensive understanding of the earthquake source process. The algorithm's potential for automated implementation, requiring few parameters, enhances its suitability for near real-time earthquake analysis.

The distribution of hydraulic-fracturing-related seismicity is largely controlled by subsurface structures, yet the physical process that governs the redistribution of injected fluids and stress heterogeneity remains underexplored due to a lack of observational constraints. In this study, we monitored an active hydraulic fracturing (HF) well for two months with a surface nodal array of 60 three-component stations. We built a high-resolution catalog comprised of 1369 events (; Mc = −0.2). Their associated seismogenic structures are resolved by seismic reflection data and a 3D velocity model obtained from ambient noise imaging. Earthquakes concentrate near the transition zone between high and low-velocity structures, with the majority $��\left(��\sim �70�\%��\right)�$ occurring on the high-velocity side, accompanied by abrupt variations in seismic attributes from reflection data. Particularly, relatively large ($��M_L��>�$ 1.0) earthquakes terminate near the edge of the high-velocity zone. This distinct interface may represent a geological boundary or strong material property contrast that acts as a physical barrier to rupture propagation and migration of seismic sequence. Locally, two key nearby clusters exhibit distinct characteristics in spatial concentration, focal mechanisms and statistical features. We suggest that variations of structural dimension (i.e., fractures vs. faults) within a complex fault system can dominate the clustering behaviors. Overall, our integrated analysis provides new constraints on mechanical interactions among seismicity, local geological structure, and fluid migration during HF operations.

The coupling of magnetic fabrics and magnetic remanences is critical in interpreting paleomagnetic data. To estimate whether primary magnetic fabrics imply primary magnetic remanences, and to assess the practicability of metamorphic rocks in magnetic study, we carried out petrographic, geochronological, rock magnetic investigations, and analyses in anisotropy of magnetic susceptibility and paleomagnetism on migmatites in the Central Tianshan, NW China. Petrological observations indicate no significant dynamic recrystallization post to the migmatization. In-situ monazite U-Pb dating suggests that the migmatization happened during ∼314–297 Ma. Rock magnetic results reveal that the magnetic properties of migmatites are dominated by biotites with minor titanomagnetites. Despite the structural and compositional complexities of migmatites, a simple magnetic fabric pattern is observed with concentrated magnetic foliations and dispersed magnetic lineations. The anisotropy degree and shape parameter significantly change from leucosomes, mesosomes to melanosomes, suggesting that the magnetic fabrics should have been acquired during the migmatization. Characteristic remanent magnetization directions were isolated from a quarter of samples with anomalous shallow magnetic inclination. Combined with available geochronological and paleomagnetic results from the Central Tianshan and neighboring blocks, the magnetic remanences preserved in the migmatites were suggested to be obtained at ∼314–303 Ma, later than the acquisition of magnetic fabrics, probably due to thermal remagnetization or resulted from long-term progressive magnetization during tectonic exhumation of migmatites. This study provides an important yet rarely reported example to manifest the decoupling of magnetic fabrics from magnetic remanences. Meanwhile, migmatites are found to be operable materials for magnetic fabric and paleomagnetic studies.

Time-reversal imaging is a critical technique for characterizing natural earthquakes and artificial sources. Traditional time reversal methods sum the extrapolated wavefields of different receivers to suppress artifacts and obtain images of the sources. Multiplication-based time-reversal imaging uses the product of extrapolated wavefields to provide source images with fewer artifacts and higher resolutions. However, although multiplication among wavefields efficiently suppresses the artifacts, sources with weaker energy are also suppressed. We combined the two imaging algorithms and proposed a combinational cross-correlation reverse time migration (CcRTM) to image multiple sources. First, the receivers were divided into several groups and independently extrapolated in reverse time. Then, n receivers were selected each time, and the geometric mean between the receiver wavefields was calculated. In the third step, images of multiple sources were obtained using the arithmetic mean of all geometric mean results with different receiver combinations. Compared with multiplication-based source location methods, our method retains the root in the geometric mean to preserve the amplitude ratio between the sources. CcRTM can be applied to image diffractions by considering subsurface small-scale diffractors as secondary sources enabling the detection of anomalies smaller than the wavelength limit. To suppress the reflection energy, we introduced an excitation time to restrict the imaging time. Synthetic and field examples demonstrated the accuracy and efficiency of the proposed imaging method.

This paper aims to solve the longstanding debate on the origin of the Comoros volcanic archipelago (Mozambique Channel, Indian Ocean) concerning whether it represents a hotspot trail or a boundary between the Lwandle and Somalia plates in possible connection with the East African Rift System (EARS). To achieve this goal, we analyzed rock samples from recently discovered and previously uninvestigated volcanoes and edifices by means of geochemistry and geochronology. Major-trace element analyses and radiometric dating (⁴⁰Ar/³⁹Ar, K-Ar, and (U-Th)/He) allow us to identify a widespread phase of Comorian volcanism initiated at 9–8 Ma, involving the Zélée, Geyser, and Leven banks, three atolls east of the Comoros. Another tectono-magmatic phase initiated at 2.5 Ma led to a N-S widening of seamount volcanism, and to the progressive development of en-échelon NW-SE structures. With this new addition of atolls and seamounts, the Comoros Archipelago becomes a ∼700 km-long, ∼200 km-wide E-W chain extending from the Cenozoic volcanoes of Madagascar to the EARS. The reactivation of this chain at 9–8 and 2.5 Ma coincides with abrupt changes in the motion of the Somalia plate relative to the Lwandle plate, and with plate boundary modifications. The en-échelon reorganization of structures also matches the kinematic evolution of Somalia relative to Lwandle, from transtension (>3 Ma) to pure dextral slip (≤3 Ma) in the northern Mozambique Channel. We conclude that the Madagascar-Comoros volcanic chain is a branch of the EARS and a plate boundary, further strengthening the link between magmatism and the Rovuma-Lwandle-Somalia plate kinematics.

Oceanic red beds, preserving primary depositional remanent magnetization, play a key role in reconstructing the Tethyan paleogeography. However, partial remagnetization caused by chemical processes could be pervasive in these rocks, leading to flawed reconstructions, and thus, differentiating secondary and primary remanences is important. In this paper, we conduct multiple X-ray diffraction, petrographic, diffuse reflectance spectroscopy, and rock magnetic analyses on the Upper Cretaceous oceanic red beds (CORBs) from the Cailangba section in the Gyangze region of the Tethyan Himalaya. Our results reveal that the CORBs contain coarse-grained detrital hematite with a narrow coercivity distribution, as well as fine-grained authigenic hematite with a broad coercivity distribution. The coarse-grained population is mainly composed of >400 nm hematite grains and unblocks close to the Néel temperature (675°C), consistent with a detrital origin. In contrast, the fine-grained population is mainly composed of <30−400 nm hematite grains and progressively unblocks below 650°C, consistent with a chemical (authigenic) origin. In addition to these two populations of hematite, a small amount of goethite, unblocking below 120°C, is detected. Due to the distinct unblocking temperature spectra of these two populations of hematite, isolating the primary detrital remanence of the coarse-grained hematite from the chemical remanence of the fine-grained hematite in the CORBs through high-resolution thermal demagnetization treatment is feasible. This study lends confidence to the paleomagnetic studies of these oceanic red beds in Tethyan paleogeographic reconstructions.

We analyze seismicity and centroid moment tensors (CMTs) on the Reykjanes Peninsula, Iceland, during the early phase of a widespread unrest period that led to multiple fissure eruptions between 2021 and 2024. We use a dense temporary seismic array, together with fiber-optic distributed acoustic sensing data, and incorporate first-motion polarities into the CMT inversion to improve accuracy, generating a total of 300 robust CMT solutions for magnitudes $��M�w�>�2.5�$, focusing on 83 reliable $��M�w�>�2.7�$ earthquakes for interpretation. The CMTs predominantly exhibit shallow strike-slip faulting, with a few normal faulting events compatible with tectonic stress. Interestingly, significant positive isotropic components are resolved, contributing up to 15% of the moment release. We also develop a new high-resolution seismic catalog of 34,407 events and show that larger shallow earthquakes at the plate boundary are preceded by the slow upward migration of microearthquakes from below, suggesting that intruding magmatic fluids interact with the oblique plate boundary to trigger slow slip events. We interpret our results as the seismic response to transtensional motion at the plate boundary in the brittle upper crust under shear, in response to stress changes induced by the intrusion of pressurized fluids in the lower crust. The complex interaction of multiple subparallel dikes with the plate boundary fault contributes to a broader deformation band that accommodates both tectonic and magmatic stresses. While the location and magnitude of the CMTs correlate with reactivated surface fractures and faults, the locations of intense, deep microseismic swarms indicate the sites of future fissure eruptions.

This study introduces a pioneering methodology for modeling the Earth’s geomagnetic field, departing from traditional reliance on current loops by employing a three-dimensional (3-D) geometric equivalent toroidal current source. We propose a 3-D unstructured magnetization vector inversion method aimed at inverting the geomagnetic vector field data set to construct an equivalent magnetization source. Subsequently, this constructed source is utilized to solve for the distribution of equivalent toroidal currents. Our objective is to elucidate and analyze potential distributions of toroidal currents within the core space. Diverging from conventional practices that estimate only seven parameters for a current loop, our research undertakes the inversion of millions of current parameters across the entire 3-D core space. This strategy eliminates the need for presuppositions regarding the current’s positions or its topological characteristics, significantly enhancing our capability to depict the possible geometry of toroidal currents. These advancements show considerable promise for modeling the geomagnetic field with high precision, transforming complex equivalent sources into more comprehensible forms, and offering profound implications for our understanding of Earth’s magnetic environment.