We process rigorously GPS data observed during the past 25 years from continental China to derive site secular velocities. Analysis of the velocity solution leads to the following results. (a) The ...deformation field inside the Tibetan plateau and Tien Shan is predominantly continuous, and large deformation gradients only exist perpendicular to the Indo‐Eurasian relative plate motion and are associated with a few large strike‐slip faults. (b) Lateral extrusions occur on both the east and west sides of the plateau. The westward extrusion peaks at ~6 mm/yr in the Pamir‐Hindu Kush region. A bell‐shaped eastward extrusion involves most of the plateau at a maximum rate of ~20 mm/yr between the Jiali and Ganzi‐Yushu faults, and the pattern is consistent with gravitational flow in southern and southeastern Tibet where the crust shows widespread dilatation at 10–20 nanostrain/yr. (c) The southeast borderland of Tibet rotates clockwise around the eastern Himalaya syntaxis, with sinistral and dextral shear motions along faults at the outer and inner flanks of the rotation terrane. The result suggests gravitational flow accomplished through rotation and translation of smaller subblocks in the upper crust. (d) Outside of the Tibetan plateau and Tien Shan, deformation field is block‐like. However, unnegligible internal deformation on the order of a couple of nanostrain/yr is found for all blocks. The North China block, under a unique tectonic loading environment, deforms and rotates at rates significantly higher than its northern and southern neighboring blocks, attesting its higher seismicity rate and earthquake hazard potential than its neighbors.
Key Points
Production of a GPS velocity solution in China with rigorous processing and accounting for effects of large earthquakes
Comprehensive analysis of distributed deformation within Tibetan plateau and Tien Shan and block‐like deformation for the rest of region
Quantification of two‐way extrusion of Tibetan plateau and clockwise rotation of its southeast borderland
We derive a detailed horizontal velocity field for the southeast borderland of the Tibetan Plateau using GPS data collected from the Crustal Motion Observation Network of China between 1998 and 2004. ...Our results reveal a complex deformation field that indicates that the crust is fragmented into tectonic blocks of various sizes, separated by strike‐slip and transtensional faults. Most notably, the regional deformation includes 10–11 mm/yr left slip across the Xianshuihe fault, ∼7 mm/yr left slip across the Anninghe‐Zemuhe‐Xiaojiang fault zone, ∼2 mm/yr right slip across a shear zone trending northwest near the southern segment of the Lancang River fault, and ∼3 mm/yr left slip across the Lijiang fault. Deformation along the southern segment of the Red River fault appears not significant at present time. The region south and west of the Xianshuihe‐Xiaojiang fault system, whose eastward motion is resisted by the stable south China block to the east, turns from eastward to southward motion with respect to south China, resulting in clockwise rotation of its internal subblocks. Active deformation is detected across two previously unknown deformation zones: one is located ∼150 km northwest of and in parallel with the Longmenshan fault with 4–6 mm/yr right‐slip and another is continued south‐southwestward from the Xiaojiang fault abutting the Red River fault with ∼7 mm/yr left slip. While both of these zones are seismically active, the exact locations of faults responsible for such deformation are yet to be mapped by field geology. Comparing our GPS results with predictions of various models proposed for Tibetan Plateau deformation, we find that the relatively small sizes of the inferred microblocks and their rotation pattern lend support to a model with a mechanically weak lower crust experiencing distributed deformation underlying a stronger, highly fragmented upper crust.
Using the measurements of ∼726 GPS stations around the Tibetan Plateau, we determine the rigid rotation of the entire plateau in a Eurasia‐fixed reference frame which can be best described by an ...Euler vector of (24.38° ± 0.42°N, 102.37° ± 0.42°E, 0.7096° ± 0.0206°/Ma). The rigid rotational component accommodates at least 50% of the northeastward thrust from India and dominates the eastward extrusion of the northern plateau. After removing the rigid rotation to highlight the interior deformation within the plateau, we find that the most remarkable interior deformation of the plateau is a “glacier‐like flow” zone which starts at somewhere between the middle and western plateau, goes clockwise around the Eastern Himalayan Syntaxis (EHS), and ends at the southeast corner of the plateau with a fan‐like front. The deformation feature of the southern plateau, especially the emergence of the flow zone could be attributed to an eastward escape of highly plastic upper crustal material driven by a lower crust viscous channel flow generated by lateral compression and gravitational buoyancy at the later developmental stage of the plateau. The first‐order feature of crustal deformation of the northeastern plateau can be well explained by a three‐dimensional elastic half‐space dislocation model with rates of dislocation segments comparable to the ones from geological observations. In the eastern plateau, although GPS data show no significant convergence between the eastern margin of the plateau and the Sichuan Basin, a small but significant compressional strain rate component of ∼10.5 ± 2.8 nstrain/yr exists in a relatively narrow region around the eastern margin. In addition, a large part of the eastern plateau, northeast of the EHS, is not undergoing shortening along the northeastward convergence direction of the EHS but is stretching.
Despite the importance of viscoelasticity in the evolution of crustal stress/strain being widely recognized, the interpretation of interseismic geodetic measurements for assessing earthquake ...potential is still based overwhelmingly on elastic models. The reasons for this disparity include conflating deformation rates with deformation itself and the lack of a succinct representation of the seismic readiness of a locked fault in a viscoelastic Earth. Using a classical viscoelastic model for strike‐slip faults, we reiterate the commonly overlooked message that, if the recurrence interval is long, most of the strain energy for the next earthquake accrues early in the cycle, and low strain rates later in the cycle by no means indicate diminished rupture potential. Fault stress stays near failure for much of the late interseismic period which may explain why slow slip‐rate faults have more variable recurrence intervals than fast slip‐rate faults. We propose to use displacement deficit instead of slip deficit to represent seismic readiness.
Plain Language Summary
Modern satellite measurements can reveal how quickly faults are being loaded by tectonic plate motions, and seismic hazard models use these loading rates as proxy for the likelihood of a pending earthquake. However, because of the partially fluid‐like behavior of Earth's interior, these loading rates have actually evolved with time since the last rupture. For faults with long intervals between successive earthquakes, these rates slow down substantially as the next event draws near. We, therefore, caution that slow rates of loading should not be assumed to reflect limited earthquake potential.
Key Points
Because of viscoelasticity, faults with long recurrence intervals accrue most of their elastic strain early in the interseismic period
Strain rates should not be conflated with stored strain, and slow geodetic deformation rates do not imply limited earthquake potential
For strike‐slip faults, “Relative Displacement Deficit” is a better measure of the earthquake readiness of a fault than “slip deficit”
Rock mechanics studies and dynamic earthquake simulations show that patterns of seismicity evolve with time through (1) accumulation phase, (2) localization phase, and (3) rupture phase. We observe a ...similar pattern of changes in seismicity during the past century across California and Nevada. To quantify these changes, we correlate GPS strain rates with seismicity. Earthquakes of M > 6.5 are collocated with regions of highest strain rates. By contrast, smaller magnitude earthquakes of M ≥ 4 show clear spatiotemporal changes. From 1933 to the late 1980s, earthquakes of M ≥ 4 were more diffused and broadly distributed in both high and low strain rate regions (accumulation phase). From the late 1980s to 2016, earthquakes were more concentrated within the high strain rate areas focused on the major fault strands (localization phase). In the same time period, the rate of M > 6.5 events also increased significantly in the high strain rate areas. The strong correlation between current strain rate and the later period of seismicity indicates that seismicity is closely related to the strain rate. The spatial patterns suggest that before the late 1980s, the strain rate field was also broadly distributed because of the stress shadows from previous large earthquakes. As the deformation field evolved out of the shadow in the late 1980s, strain has refocused on the major fault systems and we are entering a period of increased risk for large earthquakes in California.
Key Points
Earthquakes of M > 6.5 occurred in regions of highest strain rate over the past century. Its rate has increased significantly since late 1980s
From 1933 to the late 1980s, earthquakes of M ≥ 4 were more diffused and broadly distributed in both high and low strain rate regions
From the late 1980s to 2016, earthquakes were more concentrated within the high strain rate areas focused on the major fault strands
With the development of intelligent manufacturing technology, the application of intelligent machinery manufacturing technology has been widely promoted. Intelligent machinery manufacturing ...technology is a technology that integrates advanced manufacturing technology and intelligent control technology. It can realize the intelligent control of the entire manufacturing process, improve the manufacturing efficiency and product quality, and reduce the manufacturing cost. Based on intelligent manufacturing technology, intelligent machinery manufacturing technology has been developed rapidly and has been widely applied in various fields such as automotive, aviation and so on. It can achieve the goals of automation, intelligence, high efficiency, and personalization, and promote the development of various industries towards intelligent manufacturing. However, there are still challenges in the development and application of intelligent machinery manufacturing technology, such as the high cost of equipment, the difficulty in controlling the manufacturing process, and the lack of skilled workers. Future research should focus on solving these challenges and promoting the further development and application of intelligent machinery manufacturing technology.
Astrocytes (ACs) are the most widely distributed cells in the mammalian central nervous system, which are essential for the function and homeostasis of nervous system. Increasing evidence indicates ...that ACs also participate in the development of many neurological diseases and repair after nerve injury. ACs cultured in vitro provide a cellular model for studying astrocytic development, function, and the pathogenesis of associated diseases. The preparation of primary ACs (pACs) faces many limitations, so it is important to obtain high-quality ACs by the differentiation of pluripotent stem cell (PSC) or somatic cell transdifferentiation. Initially, researchers mainly tried to induce embryonic stem cells to differentiate into ACs via embryoid body (EB) and then turned to employ induced PSCs as seed cells to explore more simple and efficient directed differentiation strategies, and serum-free culture was delved to improve the quality of induced ACs. While exploring the induction of ACs by the overexpression of AC-specific transcription factors, researchers also began to investigate small molecule-mediated somatic cell transdifferentiation. Here, we provide an updated review on the research progresses in this field.
Degraded image semantic segmentation is of great importance in autonomous driving, highway navigation systems, and many other safety-related applications and it was not systematically studied before. ...In general, image degradations increase the difficulty of semantic segmentation, usually leading to decreased semantic segmentation accuracy. Therefore, performance on the underlying clean images can be treated as an upper bound of degraded image semantic segmentation. While the use of supervised deep learning has substantially improved the state of the art of semantic image segmentation, the gap between the feature distribution learned using the clean images and the feature distribution learned using the degraded images poses a major obstacle in improving the degraded image semantic segmentation performance. The conventional strategies for reducing the gap include: 1) Adding image-restoration based pre-processing modules; 2) Using both clean and the degraded images for training; 3) Fine-tuning the network pre-trained on the clean image. In this paper, we propose a novel Dense-Gram Network to more effectively reduce the gap than the conventional strategies and segment degraded images. Extensive experiments demonstrate that the proposed Dense-Gram Network yields state-of-the-art semantic segmentation performance on degraded images synthesized using PASCAL VOC 2012, SUNRGBD, CamVid, and CityScapes datasets.
Astrocytes are the most abundant cell type in the central nervous system, carrying out a wide spectrum of biological functions. During early development, neural progenitor cells in the ventricular ...zone first produce neurons, followed by macroglia in the form of astrocytes or oligodendrocytes. Although the lineage progression of oligodendrocytes has been well understood, the developmental staging of astrocytes has not been defined and the molecular mechanisms underlying their fate specification and differentiation remain largely unknown. The recent advent of sophisticated molecular biology technology, especially single‐cell sequencing, has enabled a deeper understanding of the patterning and molecular specification of astrocyte lineage. Based on the recent single‐cell sequencing data, we provide an up‐to‐date and mechanistic review of the early development and heterogeneity of astrocyte lineage in the developing cortex, and compile a list of stage‐specific markers for astrocyte development. In addition, emerging evidence suggests that under physiological conditions, mature astrocytes are partially specialized progenitor cells that have functionally adapted to local neuronal microenvironment. Under pathological or injury conditions, astrocytes are capable of reentering cell cycles and differentiating into other neural cell types under the influence of both intrinsic factors and environmental cues.
The effects of steam activation on the pore structure evolution and surface chemistry of activated carbon (AC) obtained from bamboo waste were investigated. Nitrogen adsorption–desorption isotherms ...revealed that higher steam activation temperatures and/or times promoted the creation of new micropores and widened the existing micropores, consequently decreasing the surface area and total pore volume. Optimum conditions included an activation temperature of 850°C, activation time of 120min, and steam flush generated from deionized water of 0.2cm3min−1. Under these conditions, AC with a BET surface area of 1210m2g−1 and total pore volume of 0.542cm−3g−1was obtained. Changes in surface chemistry were determined through Boehm titration, pH measurement, Fourier transform infrared spectroscopy (FTIR), and X-ray photoelectron spectroscopy (XPS). Results revealed the presence of a large number of basic groups on the surface of the pyrolyzed char and AC. Steam activation did not affect the species of oxygen-containing groups but changed the contents of these species when compared with pyrolyzed char. Scanning electron microscopy was used to observe the surface morphology of the products. AC obtained under optimum conditions showed a monolayer adsorption capacity of 330mgg−1 for methylene blue (MB), which demonstrates its excellent potential for MB adsorption applications.
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