High-velocity Zone Research Articles

Rayleigh phase velocity and azimuthal anisotropy from ambient noise data in the Sanjiang lateral collision zone in the SE margin of the Tibetan plateau

The Sanjiang lateral collision zone in the SE margin of the Tibetan Plateau is located at the east edge of the junction of the Eurasian and Indian plates. Using the continuous seismic waveforms recorded by 146 temporary and 21 permanent seismic stations in the study area, we obtain Rayleigh wave phase velocity and azimuthal anisotropy for periods 2 s to 40 s from the surface wave direct tomography method. This direct tomography method can obtain finer high-resolution results than the traditional surface wave tomography. Our results show that the low-velocity anomalies are found beneath the Lijiang-Xiaojinhe fault (LXF), Red River fault (RRF), Chuxiong fault and Tengchong volcanoes, the high-velocity anomalies are in the region of Weixi and Panzhihua at periods 5 ~ 8 s. The fast velocity directions mainly align N-S. At periods 10 ~ 15 s, the distributions of low-velocity anomalies are consistent with the strikes of LXF and RRF. At periods 20 ~ 35 s, the high- and low-velocity anomalies are bounded by the RRF, which may imply the fault is divided by the thick crust (indicated by low-velocity anomalies) and the thin crust with shallow mantle (indicated by high-velocity anomalies). The fast velocity directions at the periods 10 ~ 35 s rotate clockwise from north to south of the study area. The intensity of anisotropy in the low-velocity zone is stronger than that in the high-velocity zone, and the intensity in the north of the study area is stronger than that in the south. Results indicate the source of anisotropy may be different in each subzone.

High seismic velocity structures control moderate to strong induced earthquake behaviors by shale gas development

Moderate to strong earthquakes have been induced worldwide by shale gas development, however, it is still unclear what factors control their behaviors. Here we use local seismic networks to reliably determine the source attributes of dozens of M > 3 earthquakes and obtain a high-resolution shear-wave velocity model using ambient noise tomography. These earthquakes are found to occur close to the target shale formations in depth and along high seismic velocity boundaries. The magnitudes and co-seismic slip distributions of the 2018 Xingwen {M}_{{{{{{rm{L}}}}}}}5.7 and 2019 Gongxian {M}_{{{{{{rm{L}}}}}}}5.3 earthquakes are further determined jointly by seismic waveforms and InSAR data, and the co-seismic slips of these two earthquakes correlate with high seismic velocity zones along the fault planes. Thus, the distribution of high velocity zones near the target shale formations, together with the stress state modulated by hydraulic fracturing controls induced earthquake behaviors and is critical for understanding the seismic potentials of hydraulic fracturing.

Thermal-Hydraulic and Entropy Generation Optimization of Capsule-Type Plate Heat Exchangers With Spherical Dimples

The capsule-type plate heat exchanger (PHE) is a new type of equipment with great potential, which is characterized by the concave and convex capsule-like surface. In this article, new structures consisting of capsules and spherical dimples of PHE were proposed. Flow through a periodic unit cell with four different geometries is simulated numerically to characterize the pressure drop, heat transfer coefficients, and entropy generation rate. The numerical results show good consistency with the existing experimental data. Results show that the flow in capsule-type plate can be divided into recirculation zone and high-velocity zone. The staggered capsule structure and the spherical dimple shape generate more secondary and impinging flows, which provide higher Nusselt number and friction factor. The maximum Nusselt number area changed from the upwind region of capsule to the vicinity of dimple region because of the downwash effect and the fluid impact effect. The Nusselt number is enhanced by 19%–46%, and the friction factor is 1.21–2.9 times to that of the primary capsule-type plate. In addition, Entropy analysis illustrates that the maximum reduction in the dimensionless entropy generation rate is 43.6%.

Remnants of magma underplating by the Emeishan mantle plume within the lithosphere beneath southeastern margin of the Tibetan Plateau

The Emeishan Large Igneous Province (ELIP) is located along southeastern margin of the Tibetan Plateau, where long-wavelength crustal thickening and surface uplift have been attributed to the influx of weak crustal material from central Tibet into the lower crust beneath the Yangtze Craton. We have developed a new shear-wave velocity model for the lithosphere beneath eastern Tibet, based on a two-step linearized joint inversion technique of P-wave receiver functions (PRFs) with Rayleigh wave dispersion (10–60 s period) and Love wave dispersions (8–30 s period) for three dense seismic arrays. We applied bootstrap resampling technique to calculate the results of inversion. The resulting shear velocity model revealed two major low-velocity features in the middle–lower crust beneath southeastern Tibet. The horizontally extensive low-velocity zone (LVZ) beneath the northern Sichuan–Yunnan diamond-shaped block (SYDSB) can be interpreted as possible lower crustal flow from central Tibet, whereas the low-velocity anomaly observed beneath the Xiaojiang Fault is consistent with the presence of a partially molten layer enhanced by shear deformation along large faults. These two LVZs are separated by a lithospheric-scale high-velocity zone (HVZ) that is situated beneath the geologically inferred core of the ELIP. Based on other geophysical and geological evidence, we interpret this high-velocity anomaly body as remnants of the Emeishan plume-strengthened lithosphere that originally formed during the Permian volcanism, and we speculate that it has acted as a barrier to the hypothesized flow of lower crustal material from central Tibet since the late Cenozoic.

Tectonic Activities Description in the Ongoing Collision Zone of the Eurasia-Arabia Plates Using 2D Surface Waves Tomography

In order to better understand the regional tectonic activities of the continent-continent ongoing collision-compressed edge zone of the Eurasian-Arabic plates, 2D tomography maps of the Caucasus territory using the Rayleigh waves were generated. The 2D tomography images of this study, illustrate the large variety in surface wave propagation velocity in different complex geologic units of the Caucasus. To draw the 2D tomography maps, we accomplished a 2D-linear inversion procedure on the Rayleigh wave dispersion curves for the periods of 5 to 70 s (depth= ~180 km). To conduct this, local-regional data from ~1300 earthquakes (M≥3.9) recorded by the 49 broadband stations from 1999 to 2018 in a wide area with complicated tectonic units were used. In comparison with results of previous studies in Caucasus, the tomography maps for the long-periods (T= 50-70 s; depth ~180 km) are more influenced by the velocity structure of the uppermost mantle which demonstrate the ultralow and ultrahigh-velocity anomalies. The results for the medium-periods (30≤T≤45 s), the low-velocity zones coincide with areas thought to be correlated with underplating of the lower crust (e.g. shallow LAB), while, the high-velocity zones are usually demonstrating the presence of a normal continental crust over a stable and thick or oceanic-like lid. Short-periods (5≤T≤25 s) are more influenced by the ever-evolving deformations of the geological units, sedimentary basins, volcanic complexes, uplifts, and reveals a low-velocity small zone, on the NW slope of the Aragats volcano (depth= ~7 km), which is different from the results of other studies.

Shear wave velocity structure in the middle segment of the Xiaojiang fault zone using ambient noise tomography

The middle segment of the Xiaojiang fault zone consists of strike-slip faults with frequent strong and medium–strong earthquakes under the joint influence of NE-trending faults and deep structural characteristics. The distribution characteristics of the deep subfaults of each branch need to be revealed. Two short-period dense array survey lines are deployed in the area. Shear wave velocity structures are obtained using ambient noise tomography. The results reveal that the faults in each branch dip nearly eastward, with strike-slip characteristics in the north‒south direction. Strong velocity lateral variation infer imply that the deformation characteristics of the upper crust may be brittle. NE faults are observed, which are characterized by typical compression. The high-velocity zone in the Songming Basin may be related to the deeper upwelling of high-velocity strata in the upper crustal flow.

A computational study of 3D flow structure in two consecutive bends subject to the influence of tributary inflow in the middle Yangtze River

Enhanced understanding of turbulent flow structure in bends in natural rivers is essential for waterway regulation, navigation safety and environmental and ecological wellbeing. However, the flow structure in consecutive bends has so far remained poorly understood, especially when it is subject to the influence of tributary inflow. Here, the 3D flow structure in two consecutive bends, namely Qigongling (upstream bend) and Guanyinzhou (downstream bend), subject to the influence of tributary inflow from the Dongting Lake, in the middle Yangtze River, is numerically investigated. The RNG k-ϵ turbulence model is applied under the FLOW-3D software platform. The results show that: (1) the high-velocity zones shift from inner to outer banks in both consecutive bends. (2) No secondary current cells are spotted at the entrance of either bend. At the bend apex, multiple cells of secondary currents appear in Qigongling, but not in Guanyinzhou under certain discharges. (3) Recirculation vortices occur mainly on the inner bank (small-scale) in Qigongling, but on both the inner (small-scale) and outer (large-scale) banks in Guanyinzhou. (4) With increasing mainstem (tributary) discharge, the velocity and turbulent kinetic energy enlarge (reduce). However, a decrease of the secondary current strength in Qigongling and an increase in Guanyinzhou (all increase in both bends).

Two Unconnected Low-Velocity Zones in the Eastern Boundary of the Sichuan-Yunnan Block Revealed with High-Resolution Ambient Noise Tomography

The Anninghe-Zemuhe-Xiaojiang fault zone (AZXFZ) is an important boundary fault zone on the southeastern margin of the Tibetan Plateau, with frequent strong earthquakes. Previous studies have imaged widespread low-velocity zones in this area. However, there are still many disputes on the connectivity and genesis of the low-velocity zones. In this study, we obtain the Rayleigh wave phase velocity dispersion curves at 4–25-s periods using observations from 378 broadband stations located near the AZXFZ. The new 3D S-wave velocity model has a lateral resolution of about 30 km in 0–35-km depth and is obtained by direct inversion of surface wave dispersion data. The new results clearly image two low-velocity zones and a high-velocity zone in the middle crust of the study region. The low-velocity zone on the western side of the Lijiang-Xiaojinhe fault is related to the eastward flow of crustal material and the movement of the left lateral strike-slip faults in the Tibetan Plateau, while the low-velocity anomaly distributed along the Daliangshan fault and Xiaojiang fault is the superimposition effect of shear heating of the faults and upwelling of mantle material. The uplift of Gongga Shan is a combination of the continuous accumulation of crustal material in the middle and lower crust of the southeastern margin of the Tibetan Plateau as well as the bending and compression of the Sichuan-Yunnan Block and the Xianshuihe-Anninghe fault zone.

Three-dimensional body wave velocity structure and seismogenic structure for the 2022 MS 6.8 Luding earthquake sequence in Sichuan, China

An MS 6.8 earthquake struck the Luding county in the southeastern section of the Xianshuihe fault on 5 September 2022, causing heavy casualties and serious property losses. Using the data of 61 seismic stations surrounding the focal area, we utilize the machine learning-based LOC-FLOW for phase picking and association, and obtain a total of 13,496 aftershocks. We also collate 2,331 preshocks near the mainshock. We then conduct event relocation and three-dimensional P- and S-wave velocity structure inversion by double-difference tomography. The catalog we obtained has higher accuracy and completeness than the manual catalog. The relocation results show that the mainshock struck the Moxi section of the Xianshuihe fault at 9.2 km depth. There is a southeast-striking seismic strip of 35 km long at 5–13 km depth, and two relatively shallow seismic clusters exist to the west and northwest of the mainshock. Furthermore, there is an obvious seismic gap to the northwest of the mainshock. Based on the spatial pattern of the aftershock sequence, we speculate that the Moxi section of the Xianshuihe fault is the seismogenic fault. The earthquakes are mainly located in the regions of low velocity and low Poisson’s ratio, which is consistent with the granite that is geologically distributed along the southeast section of the Xianshuihe fault. There are two high-velocity zones located to the northwest and southeast of the mainshock, which are speculated to have controlled the rupture scale of the MS 6.8 Luding earthquake.

Relative effect of hydraulics, physico-chemistry and other biofilm algae on benthic cyanobacteria assemblages in a regulated river

The development of benthic cyanobacteria currently raises concern worldwide because of their potential to produce toxins. As a result, understanding which measures of biotic and abiotic parameters influence the development of cyanobacterial assemblages is of great importance to guide management actions. In this study, we investigate the relative contributions of abiotic and biotic parameters that may drive the development of cyanobacterial assemblages in river biofilms. First, a 2D hydrodynamic model allowed us to retrace changes in depths and velocities according to discharge at a 4 m2 resolution. From this model, we set up three hydraulic zones in each of the 4 reaches investigated along a 50-km-long river stretch. We further used univariate, multivariate and variance partitioning analyses to assess the contribution of past and present hydraulics, present physical and chemical parameters and algae to the temporal variability of cyanobacterial assemblage composition. The cyanobacterial assemblages were generally dominated by Phormidium sp., Lyngbya sp., Planktolyngbya sp. and Oscillatoria sp., four genera known to contain potentially toxic species. The highest biovolumes of cyanobacteria were present in low velocity zones in early summer and shifted to high velocity zones in late summer, highlighting the major influence of hydraulic parameters on benthic cyanobacteria settlement and development in rivers. Considering the identified genera, biofilms present a potentially high risk of toxin production. Relations between cyanobacterial development, toxin production and environmental parameters need to be further assessed to better estimate this risk.

Topographic variations of mantle transition zone discontinuities in the Java subduction zone and adjacent regions from receiver function analyses

An unprecedented number of broadband seismic data from 165 stations were utilized to constrain the topographic variations in seismic discontinuities at the top and bottom of the mantle transition zone (MTZ) in the Java subduction zone. After moveout corrections under a nonplane wavefront assumption and time-to-depth conversions based on the IASP91 Earth model, the depth undulations of two discontinuities that border the MTZ (d410 and d660) were obtained by stacking P receiver functions that were grouped into circular bins with a radius of 1°. The apparent depths exhibit systematically spatial variations that range from 385 to 427 km for the d410 and 608 to 700 km for the d660, which result in a MTZ thickness of 217–309 km. The mean values are 406 ± 12, 665 ± 19, and 258 ± 18 km, suggesting thicker than normal MTZ by an average of 8 km. The major factor that accounts for the systematic depth variations across the study area originates from the subducted slab that perturbs the entirety of the MTZ, which induces a negative thermal anomaly, high velocity zone, and abnormal water presence concentrated in the lower MTZ of western Java. In Lombok and Sumbawa Islands, after the thermal and velocity heterogeneities from the subducted slab were considered, the remnant d660 uplift is found due to a significant thermal anomaly with a magnitude of up to +200 K near the d660. In eastern Java and adjacent regions, advective thermal upwelling associated with toroidal mantle flow that traversed a slab window in central Java induces a low velocity anomaly with a magnitude that is greater than the high velocity anomaly caused by the subducted slab, which apparently depressed the d410 and d660 by the same amount.

Seismic model of the Earth's crust and upper mantle beneath the Fennoscandian Shield

Well-founded concepts of the crust and upper mantle structure of the Fennoscandian Shield were developed. Quantitative evidence for horizontal and vertical lithospheric heterogeneities was obtained. Highly detailed integrated geological and geophysical investigations, supported by superdeep drilling, have been conducted in the eastern part of the shield in recent years. Seismogeological crustal models of individual geotectonic provinces were constructed, which indicate that the structure of the crystalline crust displays a pattern of blocks, arranged hierarchically, with no persistent seismic boundaries across the entire shield. Both low- and high-velocity zones, correlatable with geological bodies, occur locally. The structural plans of contours and the velocities of various deep sections were shown to be inconsistent. We conclude that the upper mantle is laterally complex and heterogeneous, and that there is no asthenosphere in the classical sense of the word.

Lithospheric heterogeneities of northeast India and Indo-Burma region: Geodynamic implications

• Intercontinental subduction, Cenozoic volcanism and ductile sediments imaged. • Subducting Indian slab is imaged as high-Vp whilst volcanic front by low-Vp. • Dehydration of the slab, serpentinization of the forearc mantle imaged by low-Vp. • Very less seismicity due to ductility of the sediments. • Provides valuable information for intercontinental regions of analogous tectonics. In order to understand the geodynamical implications of intercontinental subduction, Cenozoic volcanism and ductile sediments in the northeast India and Indo-Burma region, a detailed 3-D P-wave tomography has been conducted using high-quality P-wave phase data recorded by local seismographic network ascribed to different agencies of India. This approach of using local earthquake data recorded by the portable seismographs installed for limited duration also provide an opportunity to adjudge the efficacy of local seismic network, which in turn enrich our understanding of intricate issues of Seismogenesis. P-wave tomographic imaging of lithospheric structure using arrival time data from local earthquakes recorded for the northeast India and Indo-Burma region revealed strong velocity heterogeneities beneath the region. The eastward subduction of the Indian slab beneath the Burmese arc with a dipping plane of intermediate-depth earthquakes has been imaged as high velocity (high-V) zones. Under the Cenozoic volcanic front in Burma, low velocity (low-V) anomalies are imaged. The low-V at shallow crustal layers may correspond to surface geological features, sedimentary materials or the faults associated with trapped fluids or loose pelgic sediments due to episodic tectonic upheavals, dehydration of the subducting Indian slab and serpentinization of the forearc mantle beneath the region, while high-V anomalies in the same depth range possibly indicate the presence of dense crystalline rocks under compressional stress that cause seismicity in the region. The distribution of seismicity is associated with major faults and lineaments associated with the distinct structural heterogeneities. The Bengal basin and the Central Burma Molasse basin exhibit low-V anomalies with very less seismicity due to ductility of the sediments. The low-V associated with the thick piles of sediments in the Bengal (>20 km) and Central Burma Molasse (≤12 km) Basin supported by the conspicuous distribution of low-Bouger gravity anomaly, which may have contributed significantly to major load along with an overthrust load of westward moving Indo-Burma ranges over the Indian lithosphere, which may amplify the stresses already acting on the Indian Plate due to load of the Himalaya, and making the region seismically more vulnerable. The present study is found to be in a good unison to the recent studies conducted in the region using different seismo-geophysical tools to different data set. The study provides valuable information on the lithospheric structures associated with seismogenesis and volcanic activity for the intercontinental regions, elsewhere in the world for our better understanding of geodynamical processes.

Anatomy of large earthquakes in North China

• Most of the large events occurred in high-V or close to the boundary between low-V and high-V zones. • Prominent low-V and high-σ anomalies in the middle and lower crust reflect crustal fluids . • Crustal fluids may originate from hot and wet upwelling flows in the big mantle wedge. • Crustal fluids affected the nucleation and generation of intracontinental large earthquakes. We present detailed 3-D isotropic P and S wave velocity (Vp, Vs) images and Vp azimuthal anisotropy in source areas of 26 large crustal earthquakes (M5.6–7.8) that occurred in North China during 1966 to 2021. Most of the large earthquakes are located in high-velocity (high-V) zones or close to the boundary between low-velocity (low-V) and high-V anomalies. Prominent low-V and high Poisson’s ratio (high-σ) anomalies are revealed in the middle and lower crust under almost all the source areas, which may reflect crustal fluids. The low-V and high-σ anomalies may cause local thinning and weakening of the brittle seismogenic layer above them. The crustal fluids may originate from hot and wet upwelling flows in the big mantle wedge (BMW) beneath East Asia due to corner flows in the BMW and deep dehydration reactions of the stagnant Pacific slab in the mantle transition zone.

Experimental Study on Damage Characteristics of Coal Samples under True Triaxial Loading and Dynamic Unloading

Abstract Coal bursts are one of the formidable hazards in underground coal mines, yet it is still not fully explored due to the complex stress environment that exists during mining. To better understand the bursting mechanism of coal under real-time mining conditions, it is necessary to develop an experimental method capable of reproducing in situ stress and loading-unloading paths of coal in in situ conditions. In this study, a self-developed true triaxial testing system was used to investigate the damage and failure characteristics of coal samples under true triaxial loading and dynamic unloading conditions. Acoustic Emission (AE) monitoring was used to capture the fracturing of the loaded coal. Passive Velocity Tomography (PVT) and Cumulative AE Energy Density (CAEED) were used to analyse damage evolution characteristics of the coal samples under true triaxial loading conditions. A high-speed camera was used to record the failure of the coal samples when the minimum principal stress σ3 was suddenly unloaded. It was found that continuous coal damage occurred primarily during the true triaxial loading period. The peak number of AE events in the coal samples increased and then dropped as σ1 levels increased. High and low wave velocity zones in the coal samples represent regenerations of the high-density zone and fracture emergence, respectively. Significant energy release zones transferred and expanded as the triaxial loading level increased. Under significant triaxial loads, the coal samples failed and were severely damaged, and the dynamic unloading of σ3 caused ejections of coal fragments at low velocities. The outcome of this study provides in-depth understanding of the failure mechanism of coal under in situ conditions.

Slab remnants beneath the Myanmar terrane evidencing double subduction of the Neo-Tethyan Ocean.

Closure of the Neo-Tethyan Ocean is one of the most significant tectonic events of the Cenozoic, forming the longest continental collision belt on Earth and influencing global climate and biodiversity. However, whether late Mesozoic subduction of the Neo-Tethyan Ocean occurred along one single or a double subduction system remains controversial. Here, upper mantle imaging from seismic tomography and waveform modeling in the Myanmar region reveals two prominent, parallel, slab-like structures with high seismic velocities that trend to the north-south and dip to the east. The western high-velocity zone has been observed previously and represents the modern subducting slab. The eastern zone has not been previously reported and exhibits high-velocity anomalies of 1.0 to 2.5% to a depth of ~300 km. This zone likely represents a remnant of another Neo-Tethyan oceanic slab that subducted ~40 million years ago. Double subduction of the Neo-Tethyan Ocean during the late Mesozoic to early Cenozoic requires reevaluation of previous tectonic models.

A Numerical Performance Analysis of a Rim-Driven Turbine in Real Flow Conditions

The tidal turbines represent a new frontier for extracting energy from tides source. Despite the technology being mature, new solutions aimed at improving performance, reliability with reduced environmental impact, manufacturing and installation costs are currently under investigation. The Rim-driven turbine (abbreviated as RDT) was recently proposed. A RDT resembles a ducted turbine (abbreviated as DT), as both contain blades and a duct. The present study aims at investigating the detail performance and flow field of a RDT in a real flow based on the China Zhaitang Island’s tidal current data. To show the difference between the RDT and DT, simulations are also performed on the corresponding DT. It is found that the power and thrust for the two configurations exhibit time-periodic behavior that is consistent with the wave frequency. At axial flow, the fluctuation amplitude on the power and thrust increase with the increase of tip speed ratio. The RDT has higher power output when operating at lower tip speed ratio and has a potential reduction in flow resistance and disturbance with respect to the DT. At yawed flow, the fluctuation amplitude on the power and thrust decrease with the increase of yaw angle. The RDT has less capable of compensating the effect of yawed inflow in reducing the power than the DT at larger yaw angle. In addition, the power and thrust generates micro-amplitude fluctuation integrated into the main waveform, which the frequency is consistent with the turbine rotation frequency. The wake characteristics analysis reveals that the yawed flow field is more turbulent, and the two configurations suffer strong unsteady flow separation along the whole span. Strong interactions are observed between the rotor’s main wake and the duct’s upper wake. The yaw angle primarily determines the downstream wake deflection direction and significantly changes the wake shape and vortex structures. Meanwhile, the wake flow is found to recover more quickly at larger yaw angle. Besides, due to the open-center of RDT, a part free-stream flow is allowed to travel through and forms an obvious high velocity zone. The presence of open-center of RDT has avoided the low velocity zone, improved the wake structure and accelerated wakes recover, which seems to give an advantageous effect in operating a RDT.

Seismogenesis of the 2021 Mw 7.1 earthquake sequence near the northeastern Japan revealed by double-difference seismic tomography

Recently, a Mw 7.1 earthquake struck the Pacific coast of northeastern Japan on 2021/02/13. To investigate the cause of this earthquake and its aftershocks, we applied a Vp/Vs model-consistency constrained double-difference (DD) seismic tomography method to the earthquake arrival time data from the dense seismic networks in Japan to image the velocity structures at the hypocenter areas. Compared to the conventional DD tomography, the new method can determine the Vp/Vs model with high resolution and precision. The reliability of the seismic tomography results is testified by checkerboard resolution test. The velocity profiles show that the oceanic crust and uppermost part of the oceanic mantle are characterized by low Vs and high Vp/Vs due to hydration reaction, while the lower oceanic mantle is associated with high Vs and low Vp/Vs anomalies that are likely caused by serpentine dehydration. The mainshock of the Mw 7.1 earthquake sequence is located at the boundary between the low velocity layer and underlying high velocity zone. The aftershocks are mainly distributed within the low velocity layer. The rupture plane inferred from the aftershock distribution and mainshock focal mechanism solution has penetrated ∼10 km into the slab and extended ∼50 km along a direction nearly parallel to the trench. These observations have suggested that the Mw 7.1 earthquake sequence occurs as a result of reactivation of a pre-existing fault likely created at the outer-rise before subduction. The association of the mainshock with the velocity anomaly edge suggests that this earthquake sequence is probably caused by dehydration of the mantle serpentines, which increases the pore pressure on the fault. Besides, the variation of rock mechanics at the hypocenter area of the mainshock also facilitates the nucleation of the whole earthquake sequence.

Effect of the wear of supersonic oxygen lance on the stirring characteristics and metallurgical effects in the converter steelmaking process

ABSTRACT Studying the variation in jet characteristics of an oxygen lance nozzle is of great significance for the converter smelting process. A full-size geometric model of a 120-t converter was established and the effects of a worn oxygen lance nozzle exit on the gas jet, stirring characteristics, and molten bath velocity distribution were studied. An increasing wear angle increases the nozzle exit velocity, increases the jet velocity attenuation, decreases the area of the longitudinal high-velocity zone of the molten bath, increases the area of the low-velocity and dead zones, worsens the molten steel flow, and decelerates the reaction rate. Then, industrial tests were conducted using a 120-t converter. When the wear angle increased from 0 to 20°, the phosphorus content, carbon–oxygen equilibrium, and TFe content in the slag increased from 0.029%, 0.0023, and 12.92% to 0.032%, 0.0028, and 14.58%, respectively. This study has important implications for optimizing the oxygen supply in converters.

Crustal structure beneath the northeastern margin of the Tibetan plateau and its surrounding regions revealed by direct surface wave radial anisotropy tomography

We assemble the continuous waveform data recorded by 571 broadband temporary seismic stations from 2014 to 2015 in the northeastern (NE) margin of the Tibetan plateau and its surrounding regions. Rayleigh and Love wave phase velocity dispersion curves (T = 5–50 s) are obtained by the image transformation technique. Then the phase velocity dispersion data are used to jointly invert the 3-D shear wave velocity (Vs) and radial anisotropy (ξ) models in the study region with the direct surface wave radial anisotropy tomography (DRadiSurfTomo) method. The ξ is negative and positive in the upper crust and mid-to-lower crust, respectively, indicating that the crustal deformation pattern is depth-dependent. The middle crust beneath the NE margin of the Tibetan plateau generally exhibits positive ξ. Two low-velocity zones (LVZs) are detected beneath the Songpan-Garzê block and the western Qinling orogen as well as the northern Qilian orogen. High-velocity zone (HVZ) and positive ξ are characterized in the mid-to-lower crust beneath both the Alxa block and the Ordos basin. Combining with the previous results, we propose these two blocks, as a whole belonging to a part of the North China Craton (NCC), effectively restrict the northeastward growth of the Tibetan plateau. The uneven crustal deformation along the boundary between the NE margin of the Tibetan plateau and its surrounding regions is likely to be affected by the far-field stress originating from the collision between the Indian and Eurasian plates.