Search

Earth’s upper atmosphere over low latitudes is influenced by the equatorial electrodynamics. Its influence can also be modulated by the thermospheric winds. The effect of these two forces on the thermospheric neutral behaviour in the daytime can be investigated by measuring the variations in the OI 630.0 nm dayglow emission rates as these serve as effective tracers of the altitude region of their origin. The capability to measure dayglow emissions over a large field-of-view presents a unique opportunity to investigate the upper atmospheric behaviour over large spatial extents. Diurnal measurements of OI 630.0 nm dayglow emission rates have been carried out from two different locations in India using multi-wavelength imaging echelle spectrographs, MISE, which, together cover a spatial range from 5 ° -18 ° magnetic latitude. These investigations have been carried out during January-February 2020 (winter season) when solar flux variation was nearly negligible (varied only by 4 solar flux unit from 68-72 solar flux unit). Therefore, latitudinal variations in the daily averaged oxygen dayglow emission intensities have been analyzed to assess their response to the variations in the strength of the equatorial electrodynamics and the meridional winds. The results reveal that these forces show varying effects with the poleward meridional wind contributing to an enhancement in the OI 630.0 nm dayglow emission rates closer to the magnetic equator and a decrement as one moves away from the equator. The equatorial electric field effect, however, continues to be equally effective in the low-latitudes region under consideration.

Jiaodong is the largest gold deposit concentration area in China. In recent years, great breakthroughs have been made in deep prospecting, and it has become the third largest concentration area of gold deposits in the world. A series of prospecting discoveries in the Jiaodong area provided the basic conditions for summarizing the regional metallogenic law, constructing the deposit model, carrying out research on the genesis of the deposit and innovating metallogenic theory. The Jiaodong gold deposits are mainly distributed in Northwest Jiaodong, Qi-Peng-Fu and Mu-Ru metallogenic regions, and mainly occur in Precambrian metamorphic rock series, Jurassic Linglong-type granite, Early Cretaceous Guojialing-type granite and Laiyang group. The orebodies are controlled by Sanshandao, Jiaojia, Zhaoping, Xilin-Douya, Jinniushan and other major ore-controlling fault zones. The main mineralization types include altered rock-type, quartz vein-type, stockwork type, sulfide quartz vein-type, interlayer detachment zone-type, altered conglomerate-type, basin margin fault breccia-type and pyrite carbonate vein-type and so on. The important progress of deep prospecting is summarized: two super giant deposits have been evaluated in the Sanshandao and Jiaojia areas; the amount of altered rock-type gold resources identified by deep prospecting has exceeded that of quartz vein-type gold deposits in the Linglong gold deposit field; the Hushan large scale gold deposit has been discovered in Qixia gold deposit field; and the Liaoshang large-size gold deposit is a new discovery of deep prospecting in Pengjiakuang gold deposit field. The ore-controlling faults of gold deposits have several changing steps with dip angle varying from steep to gentle along the dip angle. The gold ore bodies are mainly enriched in sections along the steep, gentle turning points and relatively gentle parts of the fault dip angle, forming a stepped distribution pattern. In the Early Cretaceous, the subduction and rollback of the Paleo-Pacific plate induced crust mantle interaction, resulting in large-scale magmatic and fluid activities. The crust tension and magma uplift form the dome extension structure of granite, which provides a channel for the migration of ore-forming fluid and also provides favorable space for the deposition of ore-forming fluid.

This study investigated the impact of a non-causative fault on the dynamic response of a nearby lined tunnel under the incidence of plane SV waves using the indirect boundary element method . The effects of several critical parameters, such as the incident frequency, the inclination degree of the fault, the distance between the fault and the tunnel on the hoop stress of the lined inner and outer walls, were explored intensively. The numerical results indicated that the non-causative fault could significantly change the hoop stress distribution of inner and outer surfaces of the tunnels. In general, for the vertically incident seismic waves, when the tunnel was located in the foot wall (under the fault), the hoop stress within the tunnel was significantly greater than that of the tunnels in the non-fault half space, with an amplification factor of up to 117%. The amplification effect became more pronounced as the fault dip angle increased. However, when the tunnel was located in the hanging wall (above the fault), the non-causative fault could produce a significant shielding effect on the dynamic response of the tunnel under high frequency wave incidence, with the reduction of hoop stress being up to 81%. For low-frequency waves, though, the fault could lead to an increase of the hoop stress of the tunnel of up to 152%. The research results will provide a reference for the seismic design and safety protection of underground structures in non-causative fault sites.

Layered rocks pose the challenge of wellbore stability in drilling engineering because of the anisotropic mechanical properties caused by the distinct weak planes. To understand the significant anisotropy of layered rocks in real formation condition, true triaxial compression tests are conducted by numerical simulation in this study. It is revealed that the mechanical responses of layered rocks are either controlled by the rock matrix or dominated by the weak plane and exhibit three different types associated with the orientations of the weak plane (including the dip direction α and dip angle β). When the orientations of the weak plane are α = 0°–90° and β = 0°, 60°–90°, the failure and strength properties of layered rocks depend entirely on the rock matrix, classified to the first type. Whereas the layered rocks with angle α ≤ 45° and β = 15°–45° fail by slipping failure along the weak plane, the relationship curves of rock strength versus the intermediate principal stress (σ2) are downward convex parabolas. In the last type, the mechanical behaviors of layered rocks with α > 45° and β = 15°–45°, involved in the changes of failure mode and the strength curve, are complex. Besides, the limitation of the simulation is discussed, and further studies on layered rocks are essential.

The uniaxial compression tests were conducted on granite samples with different joint dip angles to more favorably explore the influences of the nonconsecutive joint on mechanical properties and deformation characteristics of the rock mass. The stress-strain curves, deformation and strength characteristics, and energy evolution process of the samples were analyzed. Numerical simulation using particle flow code (PFC) is employed to study the crack propagation process. The mode of jointed and fractured rock was investigated. The research results showed a significant reduction in both the peak strength and elastic modulus of jointed samples compared with intact ones: the peak strength and elastic modulus drop to the minimum at the joint dip angle of about 45°, especially for the peak strength, which takes up about 55% of the intact samples. The fractured samples’ total energy, elastic strain energy, and dissipated energy during the uniaxial compression drop significantly relative to intact samples. The proportion of the fracture modes varies with different joint dip angles, in which the ratio of shear cracks grows at first and then declines, with the highest balance at the dip angle of 45°. The damage stress’s sensitivity to the dip angle change is greater than that of the peak stress, with reduction amplitude more extensive than the latter.

Coal wall spalling is regarded as a key technical problem influencing safe and efficient mining of large-mining-height working faces while the distribution of abutment pressure within the limit equilibrium zone (LEZ) influences coal wall spalling within a large-mining-height working face. This research attempted to explore the distribution characteristics of abutment pressure within the LEZ in a large-mining-height working face. For this purpose, the influences of the orientation of joints on mechanical characteristics of coal with joints and on the distribution of abutment pressure within the LEZ in the large-mining-height working face were analysed by theoretical analysis and numerical simulation. Research results show that the damage variable of coal with joints first rises, then decreases, and finally increases with increasing dip angle of the joints; as the azimuth of the joints increases, the damage variable first declines, then increases; the damage variable gradually declines with increasing joint spacing; an increase in the dip angle of joints corresponds to first reduction, then growth, and a final decrease of the abutment pressure at the same position in front of the coal walls; on certain conditions, the abutment pressure at the same position within the LEZ first rises, then declines as the azimuth of joints increases; with the growth of the joint spacing, the abutment pressure at the same position within the LEZ rises. The dip angle and azimuth of joints marginally affect the abutment pressure within the LEZ.

The multi-band observation, from radio to gamma-ray, plays a crucial role in constraining the emission physics and geometrical magnetospheric models of the pulsars. In this paper, We use three-dimensional magnetospheric model, with the joint of the annular gap (AG) and core gap (CG) model, to simulate the radio and gamma-ray light curves for two representative pulsars, a millisecond pulsar J2302+4442 and a young pulsar J0659+1414. It is found that for PSR J2302 + 4442, the simulated magnetic inclination angle α and viewing angle ζ are 34 ∘ and 46 ∘ , and for PSR J0659 + 1414 are 45 ∘ and 33 ∘ . This implies that the radio and gamma-ray pulse emission originates from different magnetospheric regions and the radiation geometry for millisecond and young pulsar is different. The studies show that the joint of the AG and CG model can describe the light curves not only for millisecond pulsars but also for young pulsars, and hence it can be used to explain the multi-wavelength observations of pulsars.

Anguillid eels grow in freshwater but spawn in the open ocean. The cues that guide eels over long distances to the spawning area are unknown. The Earth's magnetic field can provide directional and positional information and is likely used by catadromous eels during their spawning migration; as magnetosensitivity and compass orientation have been reported in eels. To test whether this is theoretically possible, we compared the migratory routes of five species of temperate eels that undertake long migrations with the geomagnetic field of their distribution/spawning areas. We found that, regardless of the species and although routes are different between life stages, larvae of those species always drift along paths of increasing magnetic inclination and intensity, while adults follow reverse gradients. This is consistent with an imprinting/retracing hypothesis. We propose a general navigation mechanism based on larvae imprinting on a target magnetic intensity (or inclination) at the hatching area and on the intensity (or inclination) gradient during larval drift. Years later, adults retrace the magnetic route by following the gradient of decreasing total intensity (or inclination) values that occurs towards lower latitudes. As they reach the target value, adults switch to compass orientation to stay on the target isoline and reach the spawning area. The proposed mechanism fits for all temperate eels examined. Knowledge about navigational strategies of eels is important to evaluate the effectiveness of management strategies that involve stocking of juveniles displaced from one area to another to rebuild local populations.

© 2021 The Author(s). Published by Oxford University Press on behalf of The Royal Astronomical Society.Flat slab subduction has been ascribed to a variety of causes, including subduction of buoyant ridges/plateaus and forced trench retreat. The former, however, has irregular spatial correlations with flat slabs, while the latter has required external forcing in geodynamic subduction models, which might be insufficient or absent in nature. In this paper, we present buoyancy-driven numerical geodynamic models and aim to investigate flat slab subduction in the absence of external forcing as well as test the influence of overriding plate strength, subducting plate thickness, inclusion/exclusion of an oceanic plateau and lower mantle viscosity on flat slab formation and its evolution. Flat slab subduction is reproduced during normal oceanic subduction in the absence of ridge/plateau subduction and without externally forced plate motion. Subduction of a plateau-like feature, in this buoyancy-driven setting, enhances slab steepening. In models that produce flat slab subduction, it only commences after a prolonged period of slab dip angle reduction during lower mantle slab penetration. The flat slab is supported by mantle wedge suction, vertical compressive stresses at the base of the slab and upper mantle slab buckling stresses. Our models demonstrate three modes of flat slab subduction, namely short-lived (transient) flat slab subduction, long-lived flat slab subduction and periodic flat slab subduction, which occur for different model parameter combinations. Most models demonstrate slab folding at the 660 km discontinuity, which produces periodic changes in the upper mantle slab dip angle. With relatively high overriding plate strength or large subducting plate thickness, such folding results in periodic changes in the dip angle of the flat slab segment, which can lead to periodic flat slab subduction, providing a potential explanation for periodic arc migration. Flat slab subduction ends due to the local overriding plate shortening and thickening it produces, which forces mantle wedge opening and a reduction in mantle wedge suction. As overriding plate strength controls the shortening rate, it has a strong control on the duration of flat slab subduction, which increases with increasing strength. For the weakest overriding plate, flat slab subduction is short-lived and lasts only 6 Myr, while for the strongest overriding plate flat slab subduction is long-lived and exceeds 75 Myr. Progressive overriding plate shortening during flat slab subduction might explain why flat slab subduction terminated in the Eocene in western North America and in the Jurassic in South China.

Using the ground-based multi instruments observations in Hainan and Southeast Asia, as well as space-based observations, the long lasting events of ionospheric irregularities occurred in the equatorial region of East Asia on the night of March 31, 2014 are studied. Concurrent observations at Hainan station indicate that ionospheric irregularities measured with different instruments showed distinct spatial structures and temporal variation, mainly from sunset to midnight (19-23LT) and even to post midnight. The 3-m-scale irregularities detected by VHF radar first attenuated and disappeared at 01LT, then the 400-meter-scale irregularities (GPS scintillations) vanished at 03LT, and finally the larger-scale irregularities (spread F) ended at 05LT. It provides a directly observational evidence that the larger the scale is, the latter the irregularities decay after midnight. Ionospheric irregularities near the magnetic equator (ME) and the equatorial abnormal peaks (EAPs) mainly occurred from after sunset to midnight (19-01LT), but there were distinct morphological differences after midnight. The irregularities near ME were attenuated and disappeared rapidly, while irregularities near EAPs weakened obviously, but lasted until dawn. The plasma depletions observed by the SWARM satellite in the latter half of the night were clearly related to the TEC fluctuations at JOG2 site, the ionospheric scintillations and spread F at Hainan station. The quasiperiodic structures of plasma bubbles observed by C/NOFS satellite were clearly related to the occurrence of ionospheric irregularities in Hainan and Southeast Asia, which indicated that the seeding of atmospheric gravity waves may play an important role in the generation of ESF/EPB irregularities, even in the latter half of the night.

The dip angle, length, spacing, and fracture distance of rock fissure affect the morphology of roadway after collapse. The numerical simulation software CDEM is used to simulate the morphology of roadway collapse. The Monte Carlo model is used to simulate different types of crack models in two-dimensional plane and generate different crack models. The effects of crack angle, crack length, fracture distance, and spacing on the deformation of surrounding rock are analyzed. The influence of different rock burst on the failure strap-fall modes of fissure roadway and roadway in different sections is analyzed, and the stability law of roadway is studied. Under the condition of high stress, the roadway shape has little influence on the distribution of the principal stress difference of surrounding rock, but the equivalent excavation radius determines the distribution of the plastic zone of surrounding rock. The larger the ineffective reinforcement zone is, the larger the deformation around the roadway will be. The decrease of the angle between the structural plane and the vertical stress increases the failure range of the roadway under the gravity burst pressure. Under the horizontal tectonic stress type rock burst, when the structural plane inclination angle is 0°, the two-sided caving body fills the roadway and the roof caving range becomes smaller.

Faulting would result in ground deformation and even damage to the tunnel structure. Thus, special structural designs should be made when the tunnel passes through an active fault. A single-track railway tunnel crossing a reverse fault is used to study the suitable structure type. In this paper, antidislocation structural measures such as reasonable segment length of articulated lining, cross-section shape, and thickness of lining are discussed through the numerical simulation. Firstly, the rational segment length of the articulated lining is confirmed. Stress and deformation behavior of articulated lining are also analyzed after the fault move. Then, the antifault effect of two kinds of cross-section shapes and three different lining thicknesses are compared. Researches show that the segment length of the articulated lining could be confirmed by the longitudinal distribution of maximum bending moment of lining after faulting. There are apparent stress concentrations occurring in the lining segment crossing the fault plane, and serious damage appears in the vault and wall waist of the tunnel. The horseshoe section with big curvature inverted arch is recommended to a single-track railway tunnel across an active fault. Simply increasing lining thickness is not suggested in a tunnel structure design crossing the active fault. The size of tunnel expansion and the minimum length of segment across fault plane can be geometrically determined according to fault dislocation magnitude and dip angle.

SUMMARY The 26 May 2019 MW 8.0 Peru intraslab earthquake ruptured the subducting Nazca Plate where the dip angle of the slab increases sharply and the strike angle rotates clockwise from the epicentre to north. To obtain a detailed seismic source model of the 2019 Peru earthquake, including not only the rupture evolution but also the spatiotemporal distribution of focal mechanisms, we performed comprehensive seismic waveform analyses using both a newly developed flexible finite-fault teleseismic waveform inversion method and a back-projection method. The source model revealed a complex rupture process involving a back-propagating rupture. The initial rupture propagated downdip from the hypocentre, then unilaterally northward along the strike of the slab. Following a large slip occurring ∼50–100 km north of the hypocentre, the rupture propagated bilaterally both further northward and back southward. The spatial distribution of focal mechanisms shows that the direction of T-axis azimuth gradually rotated clockwise from the epicentre northward, corresponding to the clockwise rotation of the strike of the subducting Nazca Plate, and the large-slip area corresponds to the high-curvature area of the slab iso-depth lines. Our results show that the complex rupture process, including the focal-mechanism transition, of the Peru earthquake was related to the slab geometry of the subducting Nazca Plate.

Trans-ionospheric signals such as the Global Positioning System (GPS) signals propagating through irregular ionospheric plasma structures may experience phase variation and amplitude fades causing degradation in system performance. This paper investigates the latitudinal structure of equatorial F-region irregularities (EFI) in the African region at different seasons using a GPS-based proxy index (rate of change of TEC index (ROTI)). The results obtained indicate the dependence of EFI on local time, season and latitude. Its occurrence time ranges between 19:00 and 0:00LT depending on the season. Its appearance is earlier in equinoxes, particularly in March equinox, and late in June solstice. Further, its occurrence lies generally within ± 22° magnetic latitudes for all seasons. The probability of occurrence, which is observed to be generally higher in equinoxes than solstices, is almost comparable across the entire latitudes where it was observed in equinoxes while the observations in solstices indicate a dip around the magnetic equator. Furthermore, the average seasonal value of ROTI indicates a clear latitudinal dependence; with appearance within ± (0°-12°) magnetic latitude in solstices while it extends up to 18° in equinoxes, particularly in the south. While the hemispheric asymmetry in the average seasonal values is favored by the hemispheric asymmetry of latitudinal TEC profile, the TEC gradient could help delineate the latitude of its peak occurrence. In addition, severe irregularities are mostly observed in equinoxes than in solstices across all latitudes of occurrence and are most pronounced around the crest region mainly in the south. Conversely, moderate irregularities are typically observed in solstices and are most frequent around the magnetic equator and the poleward edge of equatorial ionization anomaly (EIA) region in the northern hemisphere.

Azimuth gamma logging while drilling (LWD) is one of the important technologies of geosteering but the information of real-time data transmission is limited and the interpretation is difficult. This study proposes a method of applying artificial intelligence in the LWD data interpretation to enhance the accuracy and efficiency of real-time data processing. By examining formation response characteristics of azimuth gamma ray (GR) curve, the preliminary formation change position is detected based on wavelet transform modulus maxima (WTMM) method, then the dynamic threshold is determined, and a set of contour points describing the formation boundary is obtained. The classification recognition model based on the long short-term memory (LSTM) is designed to judge the true or false of stratum information described by the contour point set to enhance the accuracy of formation identification. Finally, relative dip angle is calculated by nonlinear least square method. Interpretation of azimuth gamma data and application of real-time data processing while drilling show that the method proposed can effectively and accurately determine the formation changes, improve the accuracy of formation dip interpretation, and meet the needs of real-time LWD geosteering.

This research is monitoring equatorial geomagnetic current which causes atmospheric instabilities and affects high frequency and satellite communication. It presents the variations of Horizontal (H) and vertical (Z) component of the geomagnetic field at some Equatorial Electrojet (EEJ) Stations during quiet days. Data from five (5) observatories along the magnetic equator were used for the study. Daily baseline values for each of the geomagnetic element 𝐻 and Z were obtained. The monthly average of the diurnal variation and the seasonal variations were found. Results showed that the variations of the geomagnetic element of both H and Z differ in magnitudes from one stations to another along the geomagnetic Equator due to the differences of their geomagnetic latitude. The Amplitude curves for Z) are seen to be conspicuously opposite to that of H), and there is absence of CEJ in Z- Component but present in H- Components. The values during the pre-sunrise hours are low compare to daytime hours. Minimum variations of dH was observed during June solstice and maximum variations was observed during Equinox season. This study shows that daily variations of (H) and (Z) occur in all the stations. The enhancement in H is as a result of EEJ current.

The consequences to structures caused by permanent fault displacement has been investigated for dip-slip faulting, but not for the effect of the embedment depth on the interaction between a normal fault rupture and shallow embedded foundation. This study investigated the effect of the embedment depth on the interaction of normal fault rupture and shallow foundation using a numerical model validated with centrifuge experiments. It was found that a gapping interaction mechanism and foundation distress occurred at different foundation positions relative to the fault rupture outcrop for an embedded foundation in comparison with a surface foundation. The extent of this area depended on the combined influences of the foundation position, foundation surcharge, embedment depth, and fault dip angle. The sidewalls of the shallow embedded foundation were observed to act as kinematic constraints and had considerable influence on the rotation and displacement of the foundations. With regard to the level of rotation and displacement of the embedded foundation, the lateral earth pressure distribution on the footwall sidewall was similar to that of Rankine active earth pressure in a triangular distribution and on the hangingwall sidewall as a parabolic distribution of passive earth pressure. Foundations laid on loose soil exhibited less rotation than those on dense soil because the fault ruptures were absorbed or bifurcated around both sides of the foundation.

This study presents a dynamical model of the attitude angles of boom-type roadheader, to reveal the response characteristics of the attitude angles in steep coal seam. Based on the Lagrange equation, the dynamical model of the attitude angles of roadheader is established, then the simulation system is constructed in Simulink, to solve the dynamical model. Afterwards, a calculating method of the cutting load is proposed, to formulate the external loads of the roadheader during cutting process. Focused on the steep coal seam, of which the dip angle is 30°, the dynamical model is solved, and the solving results influenced by different factors are obtained. The results show that, the variations of roadheader’s attitude are affected greatly by the cutting load, while the influence of swing angle of the cutting arm is relatively slight. Among the three attitude angles, the pitch angle varies most greatly, which can reach up to 9.1° and 8.7° during horizontal and vertical cutting process respectively. Finally, the numerical simulation results are verified by experimental data. The dynamical model and response characteristics of roadheader’s attitude angle presented in this paper, can provide useful basis for prediction of roadheader’s operating status and rectification of roadheader’s attitude in steep coal seam. Article Highlights 1. The dynamical model of roadheader’s attitude is established, to accurately describe dynamic behaviors of roadheader during cutting process. 2. The response regularities of roadheader’s attitude in steep coal seam, under effects of different factors, are revealed comprehensively. 3. A method to calculate the cutting load is proposed, upon which the three dimension forces on the cutting head can be obtained.

The experimental and numerical responses of coal specimens were studied in this work. A supercritical CO2 explosion experiment was carried out on the coal specimens using an independently developed triaxial load platform. The characteristics of crack generation in the specimens were obtained for different initial stresses. For a better understanding of the influence of cleats in a coal seam, a MATLAB code is developed to identify the actual geometry of the cleat in the coal specimen images, enabling the geometric representation of coal with cleats. The fracturing of coal with cleats induced by supercritical CO2 explosion under initial stress is validated using a combination of smoothed particle hydrodynamics and the finite-element method. The cleat can absorb and reflect the stress wave and hinder the propagation of cracks. According to the transmittance of the stress wave, the density and size of cracks that propagate through the cleat, the influences of the dip angle of the cleat, the aperture of the cleat, and the distance from the cleat to the center of the blast hole are discussed. The results show that the greater the distance from the cleat to the center of the blast hole or the greater the aperture of the cleat, the greater the hindrance of the cleat to the propagation of the cracks. With the increase of the dip angle of the cleat, the hindrance of the cleat to crack propagation first increases and then decreases.

Joints are a common structure of heterogeneous shale rock masses, and in situ stress is the environment in which heterogeneous rock masses can be found. The existence of joint plane and confining pressure difference influences the physical properties of shale and propagation of fractures. In this study, jointed shale specimens were simulated under different confining pressures to explore the failure patterns and fracture propagation behavior of hydraulic fracturing. Different from the common research of hydraulic fracturing on signal parallel joint rock mass, the simulations in this study considered three points (parallel joint, multi-dip angle joint, and no-joint points). The effects of the single-dip angle joint, multi-dip angle joint, and confining pressure difference on the hydraulic fracture evolution and stress evolution of the jointed shale were studied comprehensively. The confining pressure difference coefficient proposed in this study was used to accurately describe the confining pressure difference. Results indicate that the larger is the confining pressure difference, the stronger is the control of the maximum principal stress on fracture evolution; by contrast, the smaller is the confining pressure difference, the stronger is the control of the joint plane on fracture evolution. Under the same confining pressure difference, the hydraulic fracture propagates more easily along the small dip angle joint plane. As the value of the confining pressure difference coefficient moves closer to zero, the hydraulic fracture propagates randomly, the tensile stress region around the fracture tip widens, and the joint planes fractured by tensile increase. This study can offer valuable guidance to the design of unconventional reservoir reconstruction.

The mechanisms and characteristics of earthquake-triggered anti-dip rock landslides remain largely unknown. In this study, the dynamic response characteristics and failure process of anti-dip layered rock slopes are investigated under strong earthquake conditions using shaking table model tests and numerical analysis. The test model uses a slope angle of 60° and steep dip angle of 75° and considers different vibration waveforms, frequencies, amplitudes, and durations. Under the same conditions, the seismic wave PGA amplification factor is higher than that of a sine wave. Under the action of the two waveforms, the PGA amplification factor increases nonlinearly with elevation owing to the interaction of the elevation amplification effect and inhibition of the slope toe. The frequency is greater than or equal to the natural frequency of the test model, but the increase is not notable below 3/5 of the slope height. Horizontally, the PGA amplification factor is larger on the top and surface of the slope. The peak PGA amplification factor shifts from the surface to the top with increasing amplitude. With increasing frequency, the PGA amplification factor reaches a peak value at the natural frequency and then decreases. Frequency has a stronger influence on the dynamic slope response than amplitude, and duration has the weakest influence. The dynamic slope failure model results show that the failure mode of an anti-dip rock slope under a seismic load involves the extension of shear cracks and tension cracks and development of step-type fractures, which trigger slope toppling and sliding failure.

Dump in the steep area of the open-pit mine is essential for safe production. The bedrock with the bumpy-surface blasting method effectively improves the stabilization of the dumpsite. The effect of the ratio and dispersion degree on the deformation and failure of the dumping bench at the largely inclined area was analyzed. Based on the limit equilibrium method, the equation about the stability factor and the blasted region ratio was deduced. Virtual experiments were performed to address how the ratio and dispersion degree affect deformation and failure. The results showed that the stability factor is a quadratic function of the ratio of the blasted area. The increase in the ratio results in a drastic reduction of displacement, and the direction of displacement significantly changes. The rise in the dispersion degree effectively reduces the displacement and shear strain increment, and the failure mode changes. There is a specific value for the ratio and dispersion degree, making the displacement and shear strain increment little. The research on bumpy surface blasting in this paper provides the theoretical foundation for the dump construction at the site with the large dip angle.

In longwall mining, the deformation and destruction of overlying strata always lag behind coal extraction. The overlying strata characteristics at the lateral boundary of the stope can be classified into four categories, i.e., Hard-Soft, Soft-Hard, Hard-Hard, and Soft-Soft. In order to analyze the effect of the above four structures, we adopt viscoelastic theory to the finite element method (FEM) and define the point safety factor to evaluate the rock damage. The accuracy of programming is verified through example verification. A modified viscoelastic-plastic FEM model is applied to analyze the performance of four overburden structures. The numerical computation results show the following: From the rupture of overburden rock to its stabilization, the duration time of four typical structures can be sorted as “Soft-Soft

Carbonaceous slate is heterogeneous and anisotropic, which has a great influence on the stability of tunnel. In this paper, by means of laboratory test, field measurement, and numerical simulation, the surrounding rock stability and plastic zone distribution characteristics of the carbonaceous slate tunnel at different intersection angles are analyzed. First, combined with the Haibaluo tunnel project, Brazilian splitting and uniaxial compression tests of jointed carbonaceous slate are performed. The test results show that the tensile strength of carbonaceous slate is related to joint dip angle. When the joint angle is 0°, the tensile strength is the largest and decreases with the increase of the joint angle. The uniaxial strength of rock decreases first and then increases. Based on the discrete fracture network (DFN) technology, a calculation model is established. The calculation results show that the maximum displacement is 0.45 m, when the dip angle of the surrounding rock joint is 45°. The field measurement also shows that the dip angle of the surrounding rock joint has an important influence on the distribution of the plastic zone. When the joint dip angle is 45°, the plastic zone develops most strongly.

Mining activities carried out above an aquifer, especially in the hanging wall of normal faults, generally involve the risk of water inrush. For a better understanding of the mechanism inducing groundwater outburst through fault floor, the analytical and numerical simulation methods were applied to investigate the process of fault activation driven by mining and hydraulic loads. The influences of the advancing distance and fault dip were conducted. The results exhibit good agreement between the theoretical calculation and the numerical simulation. The fault activation by induced tangential stress change has a positive correlation with the advancing distance and a negative correlation with the fault dip angle. The stress concentration factor increases significantly when the excavation process enters the horizontal range of fault projection, following the stress peak and failure zone approaching the coal seam from deep to shallow along the fault. For the cases with a constant advancing distance, the smaller the fault dip is, the earlier the water-inrush channel will be formed. The research results in this study reveal the theoretical mechanism of fault activation and groundwater inrush of coal seam floor above a confined aquifer and thus provide valuable insights for the prevention and risk assessment of mine water disasters in underground engineering.

Surface movement and deformation with faults differ significantly from that without faults, which the surface movement and deformation at the fault outcrop generally abnormally increase when a fault occurs in the overlying strata and loses stability as a result of mining. To explore the mechanism of abnormal surface subsidence induced by fault instability due to mining in the hanging wall and footwall, mechanical models for the fault slip and soil cantilevers were separately established. Moreover, based on numerical and similarity simulation experiment, the difficulty degrees of fault instability were compared and analysed during mining in hanging wall and footwall. The research results show that: (1) the abnormal surface subsidence at fault outcrop is caused by fracture of soil mass at the fault outcrop due to the cantilever effect. (2) The fault zone that can be stabilised during mining in the hanging wall is broader than that during mining in the footwall, and a fault remains stable when mining in hanging wall and the surface at fault outcrop is more likely to experience stepped subsidence when mining in the footwall. (3) Fault stability worsens with the growth of the fault dip angle when mining in hanging wall, the fault is certainly subjected to slip and instability when fault dip angle is lower than the internal friction angle of the rock mass within the fault zone and fault stability strengthens with increasing fault dip angle during mining in the footwall. (4) When mining in the footwall, the ratio of shear stress to normal stress at the fault outcrop is about five times that when mining in the hanging wall and the fault is more likely to undergo slip and instability during mining in the footwall. (5) As a natural weak plane in the rock mass, a fault exerts a blocking effect on the transfer of mining-induced stress and overburden movements.

To ensure safe and high-efficiency mining in the coalface with large dip angle (LDA) and large mining height (LMH), it is important to study the support stability of the coalface under the corresponding conditions. This study is based on the #3up509 coalface of the Gaozhuang Coal Mine (GCM) affiliated with the Zaozhuang Mining Area (ZMA), for which the mechanical characteristics of support in the coalface with LDA and LMH are analyzed. On this basis, the mechanical models for support tilting and sliding in the coalface are developed. Then support stability along the strike of the coalface during the normal mining period (NMP) and special mining period (SMP) is analyzed. The results show that the critical support tilting resistance during the NMP is 52.2 kN, and the critical support sliding resistance is 183.75 kN, and for the SMP, the values are 2679 kN and 4425 kN, respectively. The use of a two-leg shield support, known as ZY6600-25.5/55 (its rated working resistance is 6600 kN), is investigated, which is proved reasonable for the coalface. The influencing factors of support stability along the strike include technical parameters of the support, mining geological conditions of the coalface and specific conditions during mining. Technical measures, such as installing interlock set to fasten support and adjustable lifting jack, increasing the setting load of the support, and optimizing the support displacement method, are taken to increase the overall support stability in the coalface. The initial aim for a safe and high-efficiency mining at the #3up509 coalface has been achieved through the aforementioned measures.

Coal 3 in group A is employed as a protective layer to release long-distance coal 4 in group B in Paner colliery (approximately 80 m vertical interval) as the mining depth extends downward, which is the first engineering test in the Huainan coal mining area. To evaluate the validity of the scheme, the permeability distribution, and evolution law, gas pressure distribution characteristics, swelling deformation, pressure relief range, and gas drainage volume of the protected coal seam are analyzed using a FLAC3D numerical simulation and field measurements. Therefore, different stress-permeability models are adopted for caved, fractured, and continuous deformation zones, and a double-yield model is applied in the goaf based on compaction theory to improve the accuracy of the numerical simulation. The results indicate that the extraction of coal 3 has a positive effect on permeability enhancement and pressure relief gas drainage. However, the dip angle of coal measurements causes asymmetric strata movement, which leads to the pressure relief and permeability enhancement area shifting to the downhill side, where the permeability enhancement effect of the downhill side is better than that of the uphill side. The permeability enhancement zone is an inverted trapezoid, but the effective pressure relief range is a positive trapezoid. The permeability of the protected coal seam in the pressure relief zone is significantly higher than that in the compressive failure zone. The permeability in the pressure relief zone will decrease again due to the recompaction of the coal seam with an advancement of the longwall face. Thus, pressure relief gas drainage is suggested during long-distance protective coal seam mining to eliminate gas hazards.

To address the frequent occurrence of activation-induced rock bursts in fault zones during mining, the stress evolution and fault slip behavior of normal faults with different dip angles during mining are studied by mechanical models, numerical simulations, and engineering practice. The establishment of a mechanical model of faults and the deduction of the relationships between the fault slip and the fault dip angle θ and fault friction φ reveal the necessary conditions for fault slip. The results of an analysis of a numerical model show that the change in stress state in the surrounding rock caused by mining is the root cause of fault slip. During the mining process, the risk of fault slip changes as the working face advances, and the risk of induced fault slip is higher during mining in the footwall. With the increase in the fault dip angle, the risk of fault slip first increases and then decreases, and the most dangerous dip angle in terms of fault slip is determined. The simulation and field results are consistent with the theoretical results.

Multi-reflected echoes (MREs) and satellite traces (STs) are referred in literature as ionogram signatures of Travelling Ionospheric Disturbances (TIDs) which is a phenomenon that apparently drives spread F development mainly at nighttime mid-latitude ionosphere. A long-term statistical study has been undertaken to investigate the morphological aspect of these signatures over the lower midlatitude European station of Nicosia, Cyprus (35.19°N, 33.38°E geographic; magnetic dip. 29.38°N) by inspecting all ionograms recorded by the DPS-4D digisonde in the interval 2009–2016. The results underline the systematic manifestation of these TID signatures over Cyprus with a possible (although not quite clear) solar activity dependence and a distinctive seasonal and diurnal occurrence rate with a seasonal peak of STs during summer and of MREs during January to April. Based on the experimental results of the present study, the seasonal occurrence rate of MREs and STs is found to increase by 75% and 56% during high solar activity periods. Satellite traces are well known ionogram signatures of TIDs and mostly correlated to the nighttime spread F formation. The occurrence of mid-latitude spread Fs over European longitude sector normally increases during summer. The occurrences of TIDs are also prominent at this interval of the year over nighttime mid-latitude ionosphere. The presence of MREs as an ionogram signature of TIDs over mid-latitude ionosphere is unique in nature.

The flow of blasted ore during mining of moderately dipping medium-thick orebodies is a challenge. Selecting a suitable mining system for such ore bodies is difficult. This paper proposes a diamond layout sublevel open stoping system using fan blastholes with backfilling to mine such orebodies. To evaluate the performance of system the relationships between ore recovery and stope footwall dip angle, footwall surface roughness, drawpoint spacing and production blast ring burden were investigated. An ore recovery data set from 81 laboratory physical model experiments was established from combinations of the listed factors. Various modules in a back propagation neural network structure were compared, and an optimal network structure identified. An ore recovery backpropagation neural network (BPNN) forecast model was developed. Using the model and sensitivity analysis of the factors affecting the proposed open stope mining system, the significance of each factor on ore recovery was studied. The study results were applied to a case study at the Shandong Gold Group Jiaojia Gold Mine. The results showed that the application of a BPNN and sensitivity analysis models for ore recovery prediction in the proposed mining system and field experimental results confirm that the suggested mining method is feasible.

Tight and unconventional reservoirs have become the focus with the progress of petroleum exploration and development. Micro-fractures in these reservoirs can effectively improve reservoir permeability, and well-developed micro-fractures can serve to directly improve productivity. Compared with the centered electrical well logging method, the Micro Spherical Focused Logging (MSFL) is more suitable for micro-fracture identification due to its high resolution and near borehole wall measuring method. In this study, an anisotropic model is used to depict micro-fractured formation. First, a forward model with micro-fractured formation, borehole, logging instrument and surrounding rock is established. Subsequently, MSFL responses under different micro-fracture porosity, resistivity, dip angle and borehole radius, are calculated based on the finite element method (FEM). Finally, the MSFL responses under different micro-fracture parameters are analyzed with the response laws clarified.

The variability in the amplitudes of the lunar semidiurnal tide was investigated using maps of Total Electron Content over Brazil from January 2011 to December 2014. Long period variability showed that the annual variation is always present in all investigated magnetic latitudes and it represents the main component of the temporal variability. Semiannual and intra-seasonal (~ 120 days) oscillations were the second and third components, respectively, but they presented significant temporal and spatial variation without a well-defined pattern. Among the short period oscillations in the amplitude of the lunar tide, the most pronounced ones were concentrated between 7–11 days. These oscillations were stronger around the equinoxes, in special between September and November in almost all latitudes. In some years, as in 2013 and 2014, for instance, they appeared with large power spectral density in the winter hemisphere. There was also observed evidence of antisymetry in the amplitudes maxima and minima of the 7–11 days oscillation with respect to the magnetic equator. These characteristics are compatible with normal mode westward propagating quasi 10 days planetary wave with horizontal wavenumber equal to 1. Besides, using data from a meteor radar located at low latitudes in Brazil for November 2013, when the amplitude of the 7–11 days oscillation was strong, it was possible to identify the presence of quasi 10 days oscillation in the both zonal and meridional component of the horizontal winds. These results suggest a possible coupling process by modulation of the lunar semidiurnal tidal amplitudes that allows the propagation of the 7–11 days waves into the thermosphere-ionosphere system.

The breaking features and stress distribution of overlying strata in a steeply dipping coal seam (SDCS) differ significantly from those in a near-horizontal one. In this study, the laws governing the evolution of vertical stress release and shear stress concentration in the overlying strata of coal seams with different dip angles are derived via numerical simulation, rock mechanics tests, acoustic emissions, and field measurements. Thus, the stress-driven dynamic evolution of the overlying strata structure, in which a shear stress arch forms, is determined. Upon breaking the lower part of the overlying strata, the shear stress transfers rapidly to the upper part of the working face. The damaged zone of the overlying strata migrates upward along the dip direction of the working face. The gangue in the lower part of the working face is compacted, leading to an increase in vertical stress. As the dip angle of the coal seam increases, the overlying strata fail suddenly under the action of shear stresses. Finally, the behavioral response of the overlying strata driven by shear stresses in the longwall working face of an SDCS is identified and analyzed in detail. The present research findings reveal the laws governing the behavior of mine pressure in the working face of an SDCS, which in turn can be used to establish the respective on-site guidance.

The purpose of this paper is to study the crack initiation, propagation, and coalescence of the sandy mudstone sample with two sets of prefabricated cross-flaws under uniaxial compression. This study is different from previous studies on single or multiple parallel prefabricated flaws. The prefabricated cross-flaws are characterized by the dip of the rock bridge with the direction of the main flaw ( β ) and the angle between the direction of main and minor flaws ( γ ). The effects of these two parameters on crack initiation, propagation, coalescence, crack initiation stress, and coalescence stress are analyzed. Moreover, numerical simulation of the uniaxial compression experiments is performed using PFC2D with a flat-joint model, and the simulation results are in good agreement with those from the experiments. The results demonstrate that the dip angle of the rock bridge with the direction of the main flaw ( β ) has strong effects on the crack initiation and coalescence stresses. The larger the angle between the direction of main and minor flaws γ , the greater the crack initiation and coalescence stresses. The crack initiation stress is reduced for the case with cross-flaws compared with that with non-cross-flaws. Meanwhile, the connection type of main flaws and the width of the crack coalescence zone are difficult to observe through the experiments and are discovered from the numerical simulation.

This article presents an innovative in-field calibration method for portable triaxial magnetometers (TMs). For in-field calibration of portable sensors, it is difficult to provide accurately measured inputs to each sensitivity axis due to the unavailability of high-precision turntables. Because of this limitation, most existing in-field calibration methods often require nonlinear optimization to identify model parameters. According to the fact that the angle between the local gravity and magnetic field is invariant, a new in-field calibration approach called inclination-based calibration (I-Calibration) was proposed. The I-Calibration could reliably estimate model parameters of the magnetometers by simply using a linear least square estimator. A 12-observation icosahedron experimental scheme was performed for a microinertial measurement unit, which contains both triaxial accelerometers (TAs) and TMs. The effectiveness, as well as the robustness with the misalignments of the TAs and TMs, of the proposed calibration method, was first verified by using numerical simulations. Thereafter, in real data experiments, the proposed method was compared with an existing calibration approach, namely, magnitude-based calibration (M-Calibration), which is based on the fact that the magnitude of the local magnetic field is invariant. The calibrated results together with the comparison between the two methods demonstrated the effectiveness of the proposed method.

In fully mechanized caving mining, the earlier the top coal enters the limit-equilibrium zone, the easier it is for leakage to be induced in front of the support. As the dip angle of the seam increases, the leakage of the top coal in front of the support drastically reduces the stability of the stope support–surrounding rock system. In this study, theoretical analysis, a physical simulation experiment, a numerical simulation, and field measurements were performed to consider the influence of the coal seam dip effect on the gradual deterioration of top coal for the first time, and quantitative characterization of the limit equilibrium boundary of top coal was realized based on analysis of the continuous damage medium mechanics. The results show that the two boundaries exhibit a consistent, asymmetric ‘double arch’ distribution along the incline. The top coal in the inclined upper-middle region of the working face is the first to enter the limit-equilibrium state, whereas the inclined upper and lower regions lag behind. The initial and final boundaries of the limit-equilibrium zone are distributed from 1.24 to 3.04 m and from 0.19 to −1.95 m in front of the coal wall, respectively. The distribution of the limit-equilibrium zone boundary was verified by the leakage times of the top coal in the working face. These results could provide reference information for evaluating stope support–surrounding rock systems in fully mechanized caving mining with steeply dipping coal seams.

A seafloor geomagnetic observatory in the northwest Pacific has provided very long vector geomagnetic time-series. It was found that the time-series include significant magnetic signals generated by a few giant tsunami events including the 2011 Tohoku Tsunami. Here we report that the tsunami-generated magnetic fields consist of the weak but first arriving field, and the strong but second arriving field—similar to the P- and S-waves in seismology. The latter field is a result of coupling between horizontal particle motions of the conductive seawater and the vertical component of the background geomagnetic main field, which have been studied well so far. On the other hand, the former field stems from coupling between vertical particle motions and the horizontal component of the geomagnetic main field parallel to tsunami propagation direction. The former field has been paid less attention because horizontal particle motions are dominant in the Earth’s oceans. It, however, was shown that not only the latter but also the former field is significant especially around the magnetic equator where the vertical component of the background magnetic field vanishes. This implies that global tsunami early warning using tsunami-generated magnetic fields is possible even in the absence of the background vertical geomagnetic component.

A layered rock usually exhibits strong anisotropy due to its layered structure. In order to study the anisotropic effect on its static and dynamic tensile properties, a medium strength anisotropy slate is chosen and tested in five groups of bedding plane dip angles. The dynamic tests were carried out by a split Hopkinson pressure bar (SHPB), and the failure process of rock samples is recorded by a high-speed camera. The failure mode and strength characteristic of the slate are analyzed. The static test results show that layered structure significantly affects the failure mode, and the influence of the bedding plane depends on the degree of anisotropy. The static and dynamic “tensile strength” exhibit the “U” type strength anisotropy. For samples in the same dip angle group, the “tensile strength” shows clear dynamic strengthening effect, and the growth rate is most significant at θ = 45°.

In view of the unsymmetrical large deformation and failure phenomenon that often occurs after the excavation and support of the roadway in steep seam with weak structural plane, the numerical simulation analysis and engineering application research on the deformation and failure characteristics of its surrounding rock are carried out. The results show that the key position of asymmetric deformation is near the weak structural plane and the intersection of the roadway section and the inclined direction of the rock. On this basis, the “unsymmetrical high prestress pressure relief coupling control technology” is put forward, and the industrial test is carried out. The practice shows that the unsymmetrical coupling support technology can not only effectively solve the differential deformation of the surrounding rock but also ensure the coordinated deformation of the support structure and the surrounding rock, thus improving the overall stability of the roadway, greatly reducing the repair rate of the roadway, and saving the support cost.

Bottomside thickness parameters of eight Digisonde stations over geomagnetic equator and low latitude regions have been investigated and compared with IRI model bottomside parameter during high solar activity (years 2013–2015) of the solar cycle 24. The studied years of each station rely on the GIRO data availability. The proposed B0 (B0_Pro) are computed by using the GIRO ionospheric data and the B0 expression in [16] with an average correction factor of “0.18733”. This average correction factor is derived from an average of 144 values of monthly average correction factors at eleven stations over geomagnetic equator and low latitude regions. The Results show that the seasonal variations of B0_Pro are in good agreements with those of B0_obs evidently as compared to B0_IRI at eight stations for all four seasons. For example, in the southern hemisphere, the absolute percentage distances between B0_Pro and B0_obs range from 13% to 33% with overall averages less than 26% and regional averages of 16.5%, but those between B0_IRI and B0_obs are higher. Moreover, the correlation coefficients between B0_Pro and B0_obs always are larger than 0.87 while excluding a lowest value of “0.7041”, but those between B0_IRI and B0_obs are lower. In the southern hemisphere, two remarkable features can always be reflected by B0_Pro for all studied stations. Meanwhile, in the northern hemisphere, the B0_Pro variations of each dip latitude has unique features at different locations, local times, and seasons. The inter-station differences of B0_Pro can be seen obviously in comparison with B0_IRI and described by the impacts of EEJ strength, vertical plasma drift, and PRE from local noontime to post-sunset periods. The remarkable findings from this present study may enhance the comprehension of bottomside variability and improve the IRI predictability in the future.

This paper reports that the geometrical representative elementary volume (REV) of fractured rock masses is anisotropic, and the geometric shape of an REV is of a complex, irregular geometry. A 3D fracture network model of 98 m × 80 m × 80 m was created using the field information collected from tunnel PD254 at the Maji dam site in China. One hundred random cubes of various sizes with the same sampling direction were selected to assess the volumetric fracture intensity (P32). Changing the sampling direction along the dip direction and dip angle at a 10° increment, the REV size of each sampling direction was inferred using the Wald–Wolfowitz runs test and P32 values. The REV sizes of entire rock masses and each fracture set were calculated, and the results indicated that the REV sizes varied with the different sampling directions. The anisotropy ratio and standard deviation were employed to quantify the degree of the anisotropy of REVs. Based on the results, the anisotropy of REVs for fracture set 2 is the most significant, and that of fracture set 3 is the worst. The relationship between the anisotropy of REVs and fracture sets was discussed; one fracture set, two fracture sets, and three fracture sets were selected randomly from these simulated rock masses to evaluate the characteristics of the anisotropy of REVs. The mean value and the anisotropy of REVs increased with the number of fracture sets. The maximum REV size with a sampling direction was selected as an REV for each fracture set. Four cubes with different directions and different sizes were assembled into an irregular geometry. This geometry can represent the geometric shape of the REV of entire rock masses.

Identifying deep-seated toppling failure presents unique challenges for the study of natural slope deformation in mountainous regions. In the absence of an effective quantitative approach, this study aims to provide a comprehensive grading system in order to establish a slope engineering geological model that can evaluate the deformation of a deep-seated metamorphic toppling slope. The toppling slope used in this study, located in Zhala, southwest China, affects a large area with a deformed rock mass of over 2.5 million m3. In order to objectively reflect the intensity of rock mass toppling, the deformation phenomena of this deep-seated toppling slope are first described in detail. Then, a grading index system is proposed to evaluate the degree of toppling deformation. This comprehensive index system includes the dip angle change of the rock strata, tensile cracks, rock mass structure, weathering grade, and longitudinal wave velocity. The toppling slope is divided into four toppling intensity zones: a completely toppled zone, a highly toppled zone, a moderately toppled zone, and an un-toppled zone. The detailed description and subdivision of the degree of deep-seated toppling deformation is the basis of establishing a fine engineering geological model. Different from the previous when the bottom boundary of toppling was considered as the only potential control boundary, this paper reveals that there may be multiple potential control slip zones in the deep-seated toppling slope, and different deformation degree zones correspond to different stability. As an engineering slope, engineering treatment measures can be formulated according to the degree of toppling deformation.