Journal of Geophysical Research: Solid Earth最新文献

We have investigated from rift inception to break up, the tectonic structure, spatial segmentation, and temporal evolution along ∼600 km of the East-Ceará and Potiguar basins of the Brazil Equatorial Margin. We have determined the initial rift configuration, the onset of the formation of the continental margin, and its structural evolution into a Southern, Central and Northern Segments. A distinct tectonic structure and evolution, limited by abrupt boundaries, characterize each segment. The segmentation boundaries define linear trends in the basement that extend from under the continental shelf to the deep-water domain. The trend of the segment boundaries appears to delineate flow-lines of the opening direction. The geometry of the boundaries, and available fault and dike patterns, provide information on the orientation of paleo-stresses. We integrated the distribution, geometry and age of structures to produce an evolutionary model and related it to plate kinematics. The initial Phase 1 deformation occurred in a four-arms configuration, each with different opening direction. This configuration was modified during a kinematic reorientation, causing two arms to stop opening during Phase 2. Phase 2 extension focused along two arms, creating a margin-type structure, which readjusted internal deformation into a Central, Northern and Southern Segments. Rift extension continued adapting to a gradual kinematic change into a Phase 3, when the Southern Segment developed a transcurrent fault system. Margin extension ended during Phase 4 with the initiation of spreading cells with a distribution mimicking the main rift segmentation, which remained as segmentation giving rise to oceanic fracture zones.

Earthquake rupture directivity impacts ground motions and provides insights on fault zone properties and earthquake physics. However, measuring directivity of small earthquakes is challenging due to their compact rupture sizes and complex path and site effects at high frequencies. Here, we develop a new approach that deconvolves energy envelopes of the S wave trains to remove path and site effects and robustly resolve azimuthal variations in durations of apparent source-time functions. Our method benefits from the coherence of energy envelopes for high-frequency seismic data, which provides more stable directivity results than conventional waveform deconvolution methods. We validate our method using both synthetic tests and real observations. We apply the algorithm to determine rupture directivities of 58 magnitude 3.5–5.5 earthquakes during the 2019 Ridgecrest earthquake sequence. The rupture directivities suggest an orthogonal interlocking fault system consistent with aftershock locations. Additionally, the rupture directivity pattern appears to correlate with spatial heterogeneity in earthquake stress drops. Our energy envelope deconvolution method enables directivity measurements at smaller magnitudes than traditional approaches and has potential for constraining small earthquake rupture dynamics.

We measured the thermal conductivity of composites consisting of mid-ocean ridge basalt (MORB) and polycrystalline olivine, as an analog for partially molten systems, to investigate the influence of low degree melting on heat transport. Experiments were conducted at 1 GPa and temperatures up to 1,600 K, with MORB fractions ranging from 0.1 to 10 vol.%. Adding MORB to the olivine matrix significantly altered the composite's thermal conductivity. Prior to melting, composites containing 0.1 and 10 vol.% MORB showed the most pronounced increase in conductivity relative to pure olivine, while intermediate fractions (∼1–5 vol.%) exhibited a decrease, followed by a rise at higher MORB contents. We attribute this non-monotonic behavior to impurity–lattice interactions within the MORB-bearing olivine, which reduce lattice disorder and enhance heat transport. Upon melting MORB, the thermal conductivity of the composites decreased, with the largest reductions (∼35%) observed in the 0.1 and 10 vol.% MORB samples, indicating that the melt acts as a thermal insulator. Applied to planetary interiors, these results suggest that lateral variations in melt fraction within thermal boundary layers could generate heterogeneities in heat flow, potentially affecting mantle convection patterns and the formation or evolution of thermal plumes.

The Mutnovsky and Gorely volcanoes in Kamchatka, located 70–80 km southwest of Petropavlovsk-Kamchatsky, pose significant hazard due to their potential for explosive eruptions. Mutnovsky also hosts the Mutnovsky Geothermal Power Plant (MGPP). This study presents the first crustal-scale three-dimensional seismic velocity model derived from ambient noise tomography, utilizing data from a temporary 2023–2024 seismic network of 65 mixed broadband and short-period stations, in addition to four permanent stations. The model reveals multiple low-velocity zones: a low-velocity anomaly at 2–5 km depth below sea level is interpreted as a Mutnovsky magma chamber, while the other one at 2.5–5 km depth beneath the MGPP likely reflects an active magmatic intrusion sustaining the geothermal system. A shallow anomaly at 0.5–1 km depth beneath the MGPP is attributed to production intervals associated with geothermal boreholes. Furthermore, the model indicates hydrothermal connectivity between the Mutnovsky field and the Zhirovskoy Valley, with no apparent connection to the Vilyuchinsky Valley springs. Beneath the Gorely caldera, a wide low-velocity zone suggests the presence of unconsolidated sediments and an underlying magmatic intrusion at 2–4 km depth.

This study investigates upper mantle deformation beneath northeast (NE) China by reanalyzing shear wave splitting measurements from the WAVESArray network. We identify potential overestimations of anisotropy strength in previous studies, likely caused by sensor misorientation and misclassification of null measurements. Our analysis yields 110 well-constrained splitting measurements from 66 stations and 43 high-quality null measurements from 28 stations. The mean delay time is 0.82 ± 0.28 s, consistent with the global continental average (∼1.0 s) but significantly smaller than prior estimates. Based on the spatial coherence analysis of shear wave splitting parameters and previous P-wave anisotropy results, we conclude that the anisotropy mainly originates in the lithosphere or the upper mantle transition zone (MTZ), rather than the mantle wedge. Combining our measurements with previous shear wave splitting results, we infer that the predominant NNW-SSE trending anisotropy reflects fossilized Mesozoic extensional deformation in the lithosphere or the influence of the Paleo-Pacific Plate subduction within the MTZ. Additionally, in the easternmost Xing'an Block, localized ENE-WSW fast directions may reflect preserved Proterozoic microcontinental fragments. The solely null measurements and weak anisotropy observed around the intraplate volcanoes suggest the possible presence of localized upwelling of hot material or oriented melt pockets. These findings highlight a complex interplay of multi-scale mantle and lithospheric processes shaping seismic anisotropy in NE China, providing important insights into the geodynamic processes of the Central Asian Orogenic Belt.

The response of Earth materials to stress has a first-order control on solid-Earth dynamics ranging from earthquakes to volcanic eruptions to landslides. Thus, understanding the rheological behavior of minerals, preferentially at a micro-scale to allow process-based upscaling, has broad applications across the Earth sciences. Cracks, dislocations, and point defects are microscale agents of deformation that govern the macro-scale response of rocks under stress. Complexity in deformation behavior arises from the interplay among these defect types. Here, we deformed calcite single crystals under uniaxial loading to study defect dynamics using an array of piezo-sensors synchronized with fast-camera recordings. We demonstrate that brittle cracking co-occurs with crystal-plastic twinning deformation. Furthermore, each mechanism produces distinct impulsive ultrasonic signals. Cracking produces energetic signals often with high-frequency patterns. Meanwhile, mechanical twinning produces less energetic, shorter duration, low-frequency signals correlated with propagating twin fronts. These signals can be fit with a second derivative of a Gaussian function for the first few cycles after their onset. Our results illustrate key microscale processes that drive permanent deformation in calcite, and thus contribute to building an experimentally based, process-driven understanding of rheological behavior. We highlight the utility of using ultrasonic signals, with detailed time-series analysis, to help infer in situ microscale deformation at a range of spatiotemporal scales.

Rapid response to destructive earthquakes is an important application of the distributed acoustic sensing technology (DAS), which can exploit existing telecom fiber-optic cables as ultra-dense DAS arrays. This technique significantly reduces deployment time and records large volume waveforms. However, the large stream of DAS data necessitates efficient earthquake detection methods. We propose a new DAS earthquake detection approach that hybridizes the Array Beam Detection (ABD) and Template Matched Filter (TMF) methods. This approach is applied to detect aftershocks of the 2022 Menyuan Mw6.6 earthquake recorded by a linear DAS array with the dark fiber. The continuous DAS records are scanned by the ABD method first. During this process, if the energy of the ABD-detected event exceeds a specific threshold, the event is added to the template library, and the TMF is then used to re-scan the records within a designated time window. The ABD method detects 69.4% of the events in the network catalog. Our new approach detects 89.4% of the catalog events, representing a 20% increase in the overall detection rate. Of the newly detected events, our approach identifies 42.4% more than the ABD method. Notably, the magnitudes of 95.7% of these newly detected events are estimated to be below M2.0, indicating an enhanced monitoring capability. However, precise event locations remain challenging with the linear DAS array.

The incorporation of water in high-pressure minerals is essential for the water cycle within the interiors of terrestrial planets. Majoritic garnet, a major component in the mantles of Earth and Mars, plays a significant role in this context. In this study, we use first-principles simulations to explore water incorporation mechanisms in MgSiO₃-majorite, which is a key end-member of majoritic garnet, at conditions up to 2,000 K and 20 GPa. By dealing with the relationship between chemical potential and the Gibbs free energy changes for the reactions at equilibrium conditions, we determine the ratios of the seven potential hydrous defects. Our results reveal that the Si2 and Si3 defects, which are of the hydrogarnet-type, dominate water incorporation in MgSiO₃-majorite. In addition, we evaluate the effects of these hydrous defects on seismic wave velocities. The presence of Si2 and Si3 defects, with an expected water concentration of ∼700 ppm, has a small effect on both P-wave and S-wave velocities. Nevertheless, the influence of water on lateral variations in the seismic wave velocities of MgSiO₃-majorite, which is opposite to that found for ringwoodite, offers a potential tool for investigating compositional heterogeneities in hydrated regions of planetary mantles.

Variations in the paleointensity of the Earth's magnetic field are intrinsically linked to the evolution of planetary interior dynamics and surface environmental conditions. However, the reliability of absolute paleointensity experiments is often compromised by the non-ideal magnetic behavior of multi-domain grains and alteration of magnetic minerals. To mitigate these challenges, besides conventional rock magnetic methods, this study also employs Visible and Near-Infrared Reflectance (VNIR) spectroscopy as a rapid screening tool to identify thermally unstable mineral phases that can distort experimental results. Systematic rock magnetic analyses reveal that samples with more pronounced single-domain-like magnetic properties achieve significantly higher success rates in paleointensity experiments. The implementation of VNIR-based screening increased the average success rate of analyzed samples by a factor of 1.9 compared to magnetic selection alone. We recommend using VNIR screening with M_rs/M_s ≥ 0.16 as the sample selection criterion, which can increase the success rate threefold while maintaining sufficient sample availability. By integrating VNIR spectroscopy with conventional rock magnetic methodologies, this study presents a robust approach to enhance the reliability and success rates of paleointensity determinations.

Seismic reflection and bathymetry collected along the Ecuador–Colombia obliquely convergent margin allow the first characterization of the NNE-trending, near-trench strike-slip Ancon Fault in the possible source region of the 1906-Mw8.6–8.8 and 1979-Mw8.2 earthquakes, which produced devastating tsunamis. This study aims at highlighting the possible tsunami contribution of the fault during subduction earthquakes. The fault, which correlates with a zone of strong interseismic, inter-plate coupling, is 200-km-long, segmented and bordered by remarkable slump scars. It bounds a tectonic sliver characterized by structural and rheological variations. The south-fault segment bounds a pop-up structure that comprises an up-to-25-km-wide accretionary wedge, and a mid-slope oceanic basement block uplifted by dextral transpression. The Ancon Fault becomes dominantly reverse in a seamount collision zone, where the East-directed Galera fault takes over toward the central-fault segment. This segment shows extension reflecting a releasing fault bend. The northern-fault segment is transpressive and fans out northward. It separates the fore-arc basin from a near-trench, ∼20-km-wide, pop-up oceanic basement block. Morphology, geological structures and sediment dating support a late-Pleistocene/Holocene activity of the Ancon Fault. The fault could have ruptured concurrently with the 1906 and possibly 1979 earthquakes, and contributed to the tsunamis by producing lateral displacement and differential uplift of the tectonic sliver in a similar way as a normal fault rupture contributed to the 2011 Tohoku-Oki tsunami. Transpressional uplift and landslides associated with the rupture of strike-slip faults are plausible contributing factors to tsunamis offshore North Ecuador-South Colombia and should be considered in seismic hazard models.