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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.

In this study, the crustal shear velocity structure beneath the Indo-Burma Ranges (IBR) is estimated using inversion modeling of the receiver functions computed at seismic stations operated during 2011–2018. The inversion results describe significant variations in the shear-wave velocity (Vs), velocity ratio (Vp/Vs) and crustal thickness in and around the IBR. The Moho deepens from 41 km in the west to 70 km in the east of the IBR. It is also observed that most of the earthquakes are confined to the crust in the west of the Indo-Burma arc, whilst the east of the IBR is associated with sub-crustal earthquakes, supporting the fact that the Indian plate is dipping beneath the Burma Plate. The dip angle of the Moho in the north of the IBR is smaller (7.8o) than that in its south (9.5o). We found that an average crustal Vs of 3.5 km/s for the highest value of the Vp/Vs ratio (> 1.8) was prevalent at all the stations in the IBR, associated with mafic prehnite-pumpellyite facies basalt and hydroxyl zeolite facies basalt, which suggests that the subducting Indian slab beneath the Myanmar microplate in and around the IBR is under a state of dehydration, where intra-slab earthquakes at varying depths (> 50 km) occur. This observation is highly consistent with the earlier 3-D tomographic results obtained independently.

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.

It is well known that geological structure is one of the main predisposing factors that control landslide occurrence at regional scale. Along time, investigation of the role of structural and lithologic controls has raised the interest of specialists from various earth and planetary sciences who proposed different approaches that range from descriptive analysis to automatic detection. The aim of this study is to investigate the role of structural and lithological controls on landslide occurrence at regional scale. To achieve this, a collection of tools for calculating the TOBIA index and estimating the relationship between morphostructural and lithological conditions and landslide occurrences was developed using Python programming language. The relationship between geological structure and landslide occurrences was analyzed in three distinct landslide-prone sites in Romania, located in different geological and geomorphological contexts. The spatial distribution of the geological structure is modelled based on the TOBIA index (TOpographic/Bedding-plane Intersection Angle). The TOBIA index uses topographic slope, slope aspect, dip angle, and dip direction to divide the terrain into three categories named cataclinal, anaclinal, and orthoclinal, with each category having several subcategories. Additionally, by implementing the bivariate statistical analyses (Weight of Evidence), we investigated the relationship of landslide occurrences to the resulted morphostructural slopes, on the one hand, and to the lithological units, on the other hand. The output contrast values show an evident influence of the cataclinal slopes over landslide occurrences in homoclinal areas, with most of the scarps occurring at the contact between cataclinal and orthoclinal slopes. Fewer influences are found in areas where clay outcrops and where the geological structure has a much-diminished control over the presence of the landslides. These results contribute to a better understanding of the role of structural and lithologic controls on landslide occurrence at regional scale and furthermore could serve to a better assessment of landslide susceptibility. The results obtained on different geologic and geomorphic contexts in Romania suggest that this methodology can be applied successfully in other areas prone to landslides. For reproducibility purposes, the GIS set of tools was made available under the MIT license.

© 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.

Difficult understanding of gravity effects on the 2D vertical and inclined faults for the delineation of subsurface structure for gravity exploration is slow and cumbersome. Hence, a fast and efficient algorithm is established for the interpretation of gravity anomaly over 2D inclined and vertical fault. The method can simultaneously determine all parameters such as the depth to the top (z) and base (h), dip angle (α), amplitude coefficient (k), and location of the fault plane on the surface (x0) of a hidden thin faulted slab from the observed gravity data. The developed algorithm can effectively interpret all parameters for dipping and vertical fault even though there is no subsurface drilling information. Interpretation of all the parameters suggests that there is no uncertainty for 2D inclined and vertical fault. However, if the detachment tip of the fault is at a larger depth, then the dip of the fault shows some uncertainty. The present code has been applied to non-noisy synthetic anomaly data and Gaussian noisy anomaly. Furthermore, the algorithm was also verified on three field examples from Egypt, and the USA for exploration. The appraised value of all the parameters is found to be in decent agreement with earlier published works and borehole information wherever available.

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.

Point-bar deposits, although readily recognizable in most successions, are notoriously challenging to map and correlate accurately, particularly in the subsurface. Sedimentologic interpretations from microresistivity image logs, by contrast, offer an unparalleled method of accurately reconstructing point-bar architectural elements and mapping their distribution. Using an example from the Lower Cretaceous McMurray Formation, we demonstrate that the bedding dip profiles of stacked downstream migration, lateral accretion, and channel abandonment elements record the semicontinuous point-bar accretion of two erosionally juxtaposed large-scale channels. Microresistivity image-log analysis clearly demonstrates that bedding and architectural elements of these heterolithic point bars display discrete and predictable changes in dip angle and direction that are independent of autogenic variations in lithology. We advocate, therefore, that this approach be used to map the facies of point bars and predict their reservoir trends. The laterally accreted mud-sand couplets display a cyclic pattern that is consistent with a nonrandom recurring process. Based on the distribution of bioturbation in the mud beds and variations in sand-bed thicknesses, we argue that this recurring process was probably a monthly occurrence. By measuring the lateral-accretion bed thicknesses for what appears to be a 1-yr interval, a sedimentation rate of 86 cm/yr is estimated for these lateral-accretion beds. This deposition rate provides an upper limit required to deposit these point bars and improves the framing of the depositional model. We estimate that the two point bars in this study were each deposited over a period of a few hundred years.

Study of constraints of stock emplacement and geometry on associated skarn orebodies is significant for the understanding of the epithermal deposit system. We have chosen the typical Tongguanshan skarn ore deposit (eastern China) as our target area. The Tongguanshan stock was emplaced at the NE–SW-striking Tongguanshan anticline and is characterized by macroscopically homogeneous quartz–monzodiorite. The magnetic parameters show that the stock is dominated by oblate magnetic ellipsoids and a high degree of anisotropy (> 1.1), and this value is higher at the stock margin. The strike of magnetic foliation at the stock margin is parallel to the stock boundary with sub-horizontal magnetic lineations. A vertical NE–SW-striking magnetic foliation, which is parallel to the regional structures, is revealed inside the stock. The three-dimensional geometric modelling shows that the stock has a tongue-like geometry and the contact surface in both eastern and western sides dips to the NW, but the western side is steeper. Nevertheless, the orebodies are almost developed at the eastern side. Accordingly, we propose that the Tongguanshan stock was constructed by multiple magma pulses, initiated at the SW part of the stock, and ascended along inherited NE–SW extended fractures in the Tongguanshan anticline. The successive magma pulses either accreted by a unilateral E-wards trend or by bilateral magma accretion, which resulted in a deformation difference in the contact zone and caused uneven orebody development. Our study also shows that the strike, dip angle and curvature situation of contact surface, which affects the water–rock reaction process and distribution of the dilation zone, are important ore-controlling factors.

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.

Soft and hard rock assemblages and anchor solids have important effects on rock mechanics properties under different inclinations and assemblages, so it is of great significance to study their damage and acoustic emission. Numerical simulation software RFPA2D was used to analyze the damage and acoustic emission characteristics of soft and hard rocks under different inclinations and combinations under uniaxial compression. The results show that :(1) with the increase of contact dip Angle, the rock mass strength and peak strain decrease first and then increase; (2) The mechanical properties of the composite rock mass are affected by the contact dip Angle. With the increase of the strength of the upper hard rock, the strength and peak strain tend to decrease and then increase, and the critical contact dip Angle is 75°. (3) When the contact Angle of the composite rock mass is 0~60°, the greater the contact Angle of the composite rock mass is, the more obvious the effect of the bolt on improving the mechanical properties of the rock mass is. The research results have certain reference significance to the damage and prevention of the soft and hard combined anchor solid.

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.

Electromagnetic (EM) resistivity tools measure the electrical properties of downhole formations that are critical in determining the hydrocarbon saturation of a reservoir. In complex and heterogeneous reservoirs, both horizontal and vertical formation resistivities are required to obtain an accurate hydrocarbon saturation. For decades, wireline multicomponent induction type measurements have provided reliable determination of formation anisotropy, structural dip, and dip azimuth in wells with any orientation relative to the bedding planes. Logging-while-drilling (LWD) multi-array propagation resistivity tools have also demonstrated similar capability in deviated wells where the relative dip angle is between 45° and 90°. However, measuring anisotropy and dip in wells with a low relative dip angle still poses difficulties for LWD propagation resistivity systems because of the antenna structures employed. This paper describes the development of a new LWD EM sensor equipped with an innovative, co-located, tilted antenna structure. The tool, along with a unique processing scheme, enables the determination of horizontal and vertical resistivity as well as the dip angle and the azimuth of the formation based on an assumption of transversely isotropic (TI) formation models (Graciet and Shen, 1998) while drilling in real time. The co-located sensor design is capable of acquiring multicomponent signals that are sensitive to formation anisotropy and structural dip in wells at any orientation. Modeling studies and several field trials have proven that the design concept can detect these formation properties at any arbitrary wellbore deviation. This paper presents test results from the new technology, together with reference measurements from azimuthally compensated LWD and fully triaxial wireline resistivity measurements. A good comparison is observed in these trials, providing an independent verification of the tool performance. The azimuthal measurements of the new sensors allow for determining formation anisotropy and dip at any wellbore deviation (Bittar et al., 2011b; Bittar et al., 2012), as well as providing 360° azimuthal resistivity and geosignals and allowing a three-dimensional (3D) resistivity mapping technique for real-time decisions. Integrating the co-located antennas with deep-reading antennas in a near-bit collar further provides both anisotropy measurements and ultradeep signals very close to the bit and enhances look-ahead detection ranges for LWD applications.

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.

The dip angle of coal seam in Guanyinshan coal mine is between 32° and 39° and the first mining area is X11 and X12. According to the caving degree of the immediate roof in the gob, the intensity of pressure of the main roof is analyzed, and the dynamic load coefficient of the main roof is small. The three-dimensional simulation software FLAC is used to calculate the distance of initial caving and distance of initial pressure of working face. The initial caving distance of the immediate roof at each part of the working face is about 4 m, and the initial pressure distance of main roof is about 20 m on average. This paper analyzes the caving of the main roof: when the distance of initial pressure is 20 m, the caving height of the main roof is about 4 m; when it is pushed to 30 m, the caving height of the main roof is about 10 m; with the continuous mining of the working face, the caving height of the main roof is also increasing, when it is pushed to 90 m, the caving height of the main roof reaches 18 m. Through the analysis of the regular of underground pressure in large dip angle soft roof and floor coal seam mining, it can guide the production.

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.

Analysis of the failure mechanism of inclined coal pillars is one of the complicated issues. The wide variability of dip angles of inclined coal pillars makes it more complex. The asymmetric stress distribution and the tendency of shearing along the bedding planes make the inclined coal pillars to behave differently from the flat coal pillars. There is a need for in-depth investigation of the failure mechanism for addressing the instability problems of the inclined coal pillars. Most of the literature quantifies only the magnitudes of the mean principal stresses by classical statistics. As the stress is a second-order tensor having six independent components, the classical statistics is not appropriate to calculate the mean and variability of the principal stresses at the onset of failure of the pillars. In this paper, a comprehensive analysis is done to understand the complex failure mechanism of the inclined coal pillar using numerical modelling as well as tensorial statistics and validated the results with field measurement data of failure cases. The failure mechanism is analysed by quantification of the characteristics of the inclined coal pillars by the principal-stress magnitude and its orientation, induced at the time of failure. Since the spatial variability of the magnitudes and orientations of the induced principal stresses exist within the inclined coal pillars, the mean induced principal stresses $$\left( {\overline{{\sigma_{1} }} {, }\;\overline{{\sigma_{2} }} {\text{ and }}\overline{{\sigma_{3} }} } \right)$$ are used to quantify the stress states within it. The failure stress states within the coal pillars having different dip angles are generated by the calibrated elasto-plastic numerical modelling with the ubiquitous joint model. Several statistical parameters are calculated to quantify the stress-tensor variability and the correlation among the stress-tensor components. It is found that the correlation coefficients among the shear components increase significantly with the increase of the coal pillar dip angle. Therefore, the inclined coal pillars are highly susceptible to shear failure. The magnitudes, as well as orientations of the mean induced principal stresses within the coal pillars obtained through numerical modelling, are quantified by the tensorial as well as classical statistics. It is found that the magnitude of the mean major induced principal stress $$\left( {\overline{{\sigma_{1} }} } \right)$$ at the time of failure, i.e. the strength of the pillar decreases with the increase of the dip angles. The validation of the results with the actual stress measurement data shows that all the failed pillar cases are correctly predicted by the tensorial statistical approach whereas the classical statistical approach does not effectively predict the actual failed condition of the pillars. The study would help to characterise the behaviour of the inclined pillars and address the instability issues for safe and efficient mining of inclined coal seams.

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.

The freezing method is an effective water shut-off method for shaft construction in water-rich Cretaceous strata in Northwest China. Blasting is an efficient excavation method for vertical shafts crossing the frozen stratum. The frozen rock wall is usually composed of ice and fractured rock mass and is influenced by both the in situ stress and blasting disturbance. To study the creep behavior of fractured rock masses under subzero temperatures and dynamic disturbances, a series of conventional triaxial creep and creep-disturbance tests were carried out. The results show that the flaw dip angle and dynamic disturbance had a significant influence on the creep failure characteristics of the specimens. The creep rate and failure strain of the accelerated creep stage of the specimens under dynamic disturbance were significantly greater than those of the specimens that did not undergo dynamic disturbance. Dynamic disturbance closed and recombined the microcracks, improved the short-term bearing capacity, increased the total creep time, and reduced the creep rate of the specimens. When the load or disturbance intensity reached a certain value, the crack propagation rate and creep rate of a specimen increased, the disturbance energy stored in the rock mass was released, and the specimen suddenly failed. Therefore, this disturbance creep phenomenon must be considered when constructing freezing vertical shafts in Northwest China. Moreover, timely support should be provided for exposed ice-filled fractured rock masses to guarantee construction safety and rock mass stability.