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AbstractWhen the fault in a focal area enters the critical state, nonlinear accelerated deformation and disturbance changes may occur during tide-induced loading and unloading. In this study, the anomalies in the Korla volumetric strain caused by earth tide were investigated using a theoretical model of tidal force. Results show that the step changes in the Korla volumetric strain may be triggered by tidal force within a short time frame, ranging from a few to tens of days, prior to a moderate earthquake. The azimuthal angles at the time of step changes are mainly distributed in the ranges of 124–158° and 185–228°, and the azimuth angle at the time of many nearby medium-to-strong earthquakes occurring in this step concentration area, suggesting that the step anomalies in the Korla volumetric strain are closely related to the horizontal tide-induced force in a specific direction. Using the Schuster method, it was found that the tide-induced azimuth angle of the step changes occurred mostly at the minimum value of the solid tide, providing evidences of the modulation of the solid tide. These results may present new ideas for using crustal deformation observations for short-term earthquake predictions.

Scientific progress in the context of seismic precursors reveals a systematic mechanism, namely lithosphere–atmosphere–ionosphere coupling (LAIC), to elaborate the underlying physical processes related to earthquake preparation phases. In this study, a comprehensive analysis was conducted for two earthquakes that occurred on the sea coast through tidal force fluctuation to investigate ocean–lithosphere–atmosphere–ionosphere coupling (OLAIC), based on oceanic parameters (i.e., sea potential temperature and seawater salinity), air temperature and electron density profiles. The interrupted enhancement and diffusion process of thermal anomalies indicate that the intensity of seismic anomalies in the atmosphere is affected by the extent of land near the epicenter. By observing the evolution of the ocean interior, we found that the deep water was lifted and formed upwelling, which then diffused along the direction of plate boundaries with an "intensification-peak-weakening" trend under the action of the accelerated subduction of tectonic plates. Furthermore, the analysis shows that the seismic anomalies have two propagation paths: (i) along active faults, with the surface temperature rising as the initial performance, then the air pressure gradient being generated, and finally the ionosphere being disturbed; (ii) along plate boundaries, upwelling, which is the initial manifestation, leading to changes in the parameters of the upper ocean. The results presented in this study can contribute to understanding the intrinsic characteristics of OLAIC. [ABSTRACT FROM AUTHOR]

The aim of this paper is to investigate tidal forces in multidimensional spherically simmetric spacetimes. We consider geodesic deviation equation in Schwarzschild–Tangherlini metric and its electrically charged version. We show that these equations can be solved explicity for radial geodesics as quadratures in spaces of any dimension. In the cases of five, six and seven dimensional spaces, these solutions can be represented in terms of elliptic integrals. For spacetimes of higher dimension asymptotics of the solution are found instead. We established that the greater the dimension of space is, the stronger the tidal stretch along the radial direction in the vicinity of physical singularity is, whereas the tidal compression in direction transverse to the radial one, does not change in the leading order starting from a certain dimension. Also, in the case of non-radial geodesics, the presence of black hole electric charge does not affect the force of transverse compression in the leading order. Finally, for non-radial geodesics with nonzero angular momentum, the local properties of solutions of geodesic deviation equations in the vicinity of a singularity are studied. [ABSTRACT FROM AUTHOR]

Based on four years of spatially synchronous topographic data of the Oujiang Estuary from 2002 to 2019, the variations and physical mechanisms of estuarine evolution driven by natural conditions and human activities since the beginning of this century were analyzed. The results show that the evolution of the Oujiang Estuary has changed dramatically in the past 20 years. From 2002 to 2019, the net sediment erosion of the estuary was 163.44 million m3, and the average bed elevation of the river-dominated section (RDS), transition section (TS) and tide-dominated section (TDS) decreased by 4.61 m, 1.30 m and 2.14 m, respectively. In addition, the pattern of the shoal channel had changed, and the river facies coefficient (width–depth ratio) decreased by 16–64%. The evolution of the Oujiang Estuary is mainly caused by human activities (such as sand mining, reclamation). Sand mining is the direct cause of riverbed undercutting, and the large undercutting of riverbed terrain causes the increase in tidal power in the estuary and further causes river channel scouring. In the last 20 years, the average annual tidal range of the estuary increased by 0.19–1.14 m, and the flood discharge increased by about 17–80%, with an average value of 58%. The impact of tidal power on the evolution and development of the estuary has increased significantly. Apart from sand mining, reclamation projects such as the Wenzhou shoal outside the mouth also cause the local velocity of the tidal current section to increase, which aggravates the scouring trend of local river sections downstream. The scouring and silting changes in the Oujiang Estuary since the beginning of this century are the result of the adjustment of the estuarine system in response to the strong intervention of human activities. [ABSTRACT FROM AUTHOR]

An important aspect of general relativity is to study properties of geodesics. A useful tool for describing geodesic behavior is the geodesic deviation equation. It allows to describe the tidal properties of gravitating objects through the curvature of spacetime. This paper focuses on the study of the axially symmetric Taub–NUT metric. We study tidal effects in this metric using the geodesic deviation equation. Radial geodesics along the symmetry axis of spacetime are considered. We show that all spatial components of tidal forces always change sign under the event horizon. We find a solution of the geodesic deviation equation for all geodesic deviation vector components. It allows us to quantify the effect of the NUT-charge on the tidal properties of Taub–NUT metric. Another important feature that we found is the regular behavior of all tidal force components at all points of spacetime. [ABSTRACT FROM AUTHOR]

Scientific progress in the context of seismic precursors reveals a systematic mechanism, namely lithosphere–atmosphere–ionosphere coupling (LAIC), to elaborate the underlying physical processes related to earthquake preparation phases. In this study, a comprehensive analysis was conducted for two earthquakes that occurred on the sea coast through tidal force fluctuation to investigate ocean–lithosphere–atmosphere–ionosphere coupling (OLAIC), based on oceanic parameters (i.e., sea potential temperature and seawater salinity), air temperature and electron density profiles. The interrupted enhancement and diffusion process of thermal anomalies indicate that the intensity of seismic anomalies in the atmosphere is affected by the extent of land near the epicenter. By observing the evolution of the ocean interior, we found that the deep water was lifted and formed upwelling, which then diffused along the direction of plate boundaries with an “intensification-peak-weakening” trend under the action of the accelerated subduction of tectonic plates. Furthermore, the analysis shows that the seismic anomalies have two propagation paths: (i) along active faults, with the surface temperature rising as the initial performance, then the air pressure gradient being generated, and finally the ionosphere being disturbed; (ii) along plate boundaries, upwelling, which is the initial manifestation, leading to changes in the parameters of the upper ocean. The results presented in this study can contribute to understanding the intrinsic characteristics of OLAIC.

In this paper, we analyze the tidal effects of anti-de Sitter charged black holes. The tidal force components are obtained by Riemann tensor on tetrad basis and geodesic deviation equation. The radial components of tidal force have the same changes outside the horizon if the charge mass ratio is closer to each other, unlike in Reissner–Nordström BHs. The angular tidal forces increase infinitely with increase of charge and Λ. We derive the geodesic deviation equation on a neutral body for anti-de Sitter torus like charged black hole. We find the radial and angular tidal forces on the neutral body. Furthermore, we express the graphical behavior of radial and angular components for the most suitable initial conditions. [ABSTRACT FROM AUTHOR]

According to the statistical analysis of the time and region of rockburst, it is found that the time and region of rockburst have a certain correlation with the change of tidal force. In order to explore this correlation, the mechanism of rock burst induced by tidal force was investigated. On the basis of the mechanical model of rockburst, the mechanism of rockburst induced by tidal force was discussed by using the method of Coulomb Mohr criterion, and the rockburst induced by tidal force was analyzed from five cases. It provides a new idea for the prediction and prevention of rockbursts.

Two approaches are applied to outgoing longwave radiation (OLR) data to obtain abnormal changes before and after six earthquakes: the background field analysis (BFA) method, which focuses on statistically processing the increment of a radiation value to the multiyear average of the data; and the tidal force fluctuant analysis method, which abandons background data for many years by using the influence of tidal fluctuations to obtain incremental changes in radiation. The results demonstrate that the increase in OLR data identified via the BFA method was uncertain. In the time distribution, the occurrence time of anomalies is isolated and not continuous. In the spatial distribution, many OLR enhancement areas occurred multiple times in the nonseismic and remote seismic-related fault structure areas. In contrast, through the tidal force fluctuant analysis method a clear and consecutive OLR anomaly emerged in the seismogenic cycle of the tidal force. It corresponded with the tidal force through a unique evolution: increased-earthquake-shrink around the epicentre, consistent with the change in the law of thermal radiation during the rock-breaking process under stress, and clearly related to the earthquake's seismic tectonic stress change. It is proven that the tidal force of a celestial body may trigger an earthquake when the tectonic stress reaches its critical breaking point, and when the triggering action is a continuous rather than brief one-shot process. The in situ stress state is key. The OLR anomaly was the physical performance of underlying surface radiation from the change in seismic tectonic stress.

There is still no consensus regarding the ultimate cause of the famous 3–4-year population cycles of lemmings. According to the plant stress hypothesis, herbivore population peaks are caused by stress factors that force plants to reallocate stored defensive proteins to transportable and easily digestible N-compounds. One possible plant stress factor is ionization caused by exhalation of the radioactive noble gas radon, which is enhanced after spring tides, i.e., tides at new or full Moon. I hypothesized that increased ionization caused by radon accumulation in the subnivean space after peak spring tides, which occur close to perihelion (31 December–05 January, when the Earth–Sun distance is shortest), and at 3.8-year intervals, results in increased protein digestibility of mosses, which are important food for lemmings. Population outbreaks of Norway lemming Lemmus lemmus occurred two years after peak spring tides during 1871–1910, when also perigee (the time when the Earth–Moon distance is shortest) coincided with spring tides and perihelion. Thereafter this relationship weakened, and lemming peaks became less pronounced and more related to plant seed indices. As we have now entered a new 30-year period with coincidence of spring tide, perihelion and perigee, I predict more regular and pronounced lemming outbreaks in the next decades, unless radon accumulation is prevented by frequent lack of a stable snow cover due to global warming. • Population cycles of lemmings follow the 3.8-year cycle in peak spring tides close to perihelion, i.e., peak spring tides. • Radon exhalation is enhanced at peak spring tides. • Ionization caused by radon accumulation beneath the snowpack is a possible plant stress factor that favor lemmings. • Populations of Norway lemming peaked after peak spring tides, in particular when peak spring tides coincided with perigee. [ABSTRACT FROM AUTHOR]

The concept of regular black holes has gained attention in recent years, especially in the context of quantum gravity theories. In these theories, the existence of singularities is paradoxical as they represent a breakdown of the laws of physics. Motivated by the recent developments in this area, we study the tidal force effects in one such family of regular geometries described by the Simpson–Visser metric. We find the radial and angular force profiles for a radially in-falling particle in this spacetime and calculate the variation of the geodesic separation vector with the radial coordinate using two different initial conditions. These results are then compared with that of Schwarzschild black hole spacetime. We show that for a regular black hole, both radial and angular tidal forces show a peak outside the horizon and then fall to ultimately switch their behavior from stretching to compression and vice-versa. Also, they are finite at r = 0 unlike the Schwarzschild spacetime. It is also seen that the angular deviation profile shows an oscillating behavior for a particular initial condition. Our analysis can be used to distinguish between regular black hole, one-way and two-way wormholes and a singular black hole spacetimes. [ABSTRACT FROM AUTHOR]

Based on four years of spatially synchronous topographic data of the Oujiang Estuary from 2002 to 2019, the variations and physical mechanisms of estuarine evolution driven by natural conditions and human activities since the beginning of this century were analyzed. The results show that the evolution of the Oujiang Estuary has changed dramatically in the past 20 years. From 2002 to 2019, the net sediment erosion of the estuary was 163.44 million m3, and the average bed elevation of the river-dominated section (RDS), transition section (TS) and tide-dominated section (TDS) decreased by 4.61 m, 1.30 m and 2.14 m, respectively. In addition, the pattern of the shoal channel had changed, and the river facies coefficient (width–depth ratio) decreased by 16–64%. The evolution of the Oujiang Estuary is mainly caused by human activities (such as sand mining, reclamation). Sand mining is the direct cause of riverbed undercutting, and the large undercutting of riverbed terrain causes the increase in tidal power in the estuary and further causes river channel scouring. In the last 20 years, the average annual tidal range of the estuary increased by 0.19–1.14 m, and the flood discharge increased by about 17–80%, with an average value of 58%. The impact of tidal power on the evolution and development of the estuary has increased significantly. Apart from sand mining, reclamation projects such as the Wenzhou shoal outside the mouth also cause the local velocity of the tidal current section to increase, which aggravates the scouring trend of local river sections downstream. The scouring and silting changes in the Oujiang Estuary since the beginning of this century are the result of the adjustment of the estuarine system in response to the strong intervention of human activities.

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The evolutionary instability dynamics, which is naturally excitable in an astrophysical complex gyrogravitating partially ionised molecular cloud in a magnetic field, is herein semianalytically investigated. It is rooted in a non-ideal classical non-relativistic magnetohydrodynamic (MHD) mean-fluidic model fabric. The effects of fluid kinematic viscosity, cosmic rays and tidal force field are concurrently included. Application of a standard normal mode analysis reduces the astrocloud into a unique generalised linear quartic dispersion relation having atypical variable coefficients. A numerical illustrative analysis shows that the instability is noticeably damped (grown) in the viscous (inviscid) domains. The magnetic field and rotation have stabilising influences against the non-local self-gravity. In contrast, the cosmic ray pressure and tidal interaction destabilise the cloud along its self-gravity. We see that the ambipolar diffusion is the only non-ideal MHD factor with significant stimulus on the magneto-acoustic waves. The non-trivial results explored here match with the prior predictions both as special cases and stimulating corollaries relevant in the bounded astrostructure creation dynamics. [ABSTRACT FROM AUTHOR]

We investigate tidal effects produced in the spacetime of Schwarzschild black hole in holographic massive gravity, which has two additional mass parameters due to massive gravitons. As a result, we have obtained that massive gravitons affect the angular component of the tidal force, while the radial component has the same form with the one in massless gravity. On the other hand, by solving the geodesic deviation equations, we have found that radial components of two nearby geodesics keep tightening while falling into the black hole and after passing the event horizons get abruptly infinitely stretched due to massive gravitons. However, angular components of two nearby geodesics get stretched firstly, reach a peak and then get compressed while falling into the black hole. Moreover, we have also shown that the angular components are more easily deformed near the departure position as the mass of a black hole is smaller for a fixed graviton mass.

The attention towards links of atmospheric parameter variation and earthquakes has increased exponentially by utilizing new methods and more accurate observations. Persistent research makes it possible to gain insight into the precursor mechanism of earthquakes. In this paper, we studied the universality of detecting atmospheric anomalies associated with earthquakes based on tidal force fluctuation in China for earthquakes of Ms > 6.0, and explored the influence of tidal force on tectonic stress. The data of air temperature, geopotential height, ozone mixing ratio, and relative humidity from the National Center for Environmental Prediction (NCEP) were analyzed to reveal the spatiotemporal variation of atmospheric anomalies at multiple isobaric surfaces. Furthermore, the coupling of atmospheric parameters was investigated. The results showed that continuous solicitation exerted by tidal forces could change the strength of tectonic stress that causes earthquakes. The evolution pattern of air temperature, geopotential height, and relative humidity could be supported by atmospheric thermal vertical diffusion, while the anomalies of ozone mixing ratio was not evident. This verified the feasibility of detecting multi-parameter atmospheric anomalies associated with earthquakes based on tidal force fluctuation. Our results provide more evidence for understanding the atmospheric precursor characteristics of earthquakes.

Morphologically distinct characteristics of strike-slip deformation have not been well documented on Titan due to limited quality and coverage of observational data. However, optimal shear failure conditions may exist within Titan's shallow subsurface due to the inferred presence of a porous ice layer saturated with liquid hydrocarbons. In this study, we examine the proposed Dragonfly landing site on Titan, the Selk crater region, and investigate the area in context of possible tidal shear deformation and strike-slip faulting. For this, we use established methods of previous studies based on the Coulomb failure criterion and numerical model SatStress to calculate diurnal tidal stresses that may act to deform the region. We extracted stresses along one line of latitude (5°N) from 155°-165° E, crossing various identified geologic terrain units, and found that presently, shear failure initiated through diurnal tidal stresses can only occur if pore fluid pressures are intermediate to high (λ > 0.75) and/or the coefficient of friction of the icy crust is low (μ f < 0.3). As it is unlikely for these conditions to be present in this area, we can infer that there is currently no shear deformation occurring in the Selk crater region due to diurnal tidal stresses. The results presented here aim to advance our knowledge of structural crustal properties that promote or limit shear failure on Titan on a local scale, and to better inform the exploration of Titan through the Dragonfly mission. To gain new insights and broaden our understanding of icy worlds, it is imperative that we employ the most precise data in our modeling work. Missions like Dragonfly , Europa Clipper and ESA's JUICE will further constrain our modeling approach and can help pinpoint the most interesting locations for lander exploration and possibly for gaining access to the interior ocean of icy moons. • Numerical model SatStress used to calculate diurnal tidal stresses at Selk Crater on Titan, the proposed Dragonfly landing site. • Stresses examined along one line of latitude (5°N) from 155°-165° E, crossing various identified geologic terrain units. • Results suggest that shear failure initiated through diurnal tidal stresses can only occur if pore fluid pressures are intermediate to high. [ABSTRACT FROM AUTHOR]

On 3 August 2014, an Mw 6.2 earthquake occurred in Ludian, Yunnan Province, China (27.245° N 103.427° E). This damaging earthquake caused approximately 400 fatalities, 1800 injuries, and the destruction of at least 12,000 houses. Using air temperature data of the National Center for Environmental Prediction (NCEP) and the tidal force fluctuant analysis (TFFA) method, we derive the temperature variations in multiple air layers between before and after the Ludian earthquake. In the spatial range of 30° × 30° (12°–42° N, 88°–118° E) of China, a thermal anomaly appeared only on or near the epicenter before earthquake, and air was heated from the land, then uplifted by a heat flux, and then cooled and dissipated upon rising. With the approaching earthquake, the duration and range of the thermal anomaly during each tidal cycle was found to increase, and the amplitude of the thermal anomaly varied with the tidal force potential: air temperature was found to rise during the negative phase of the tidal force potential, to reach peak at its trough, and to attenuate when the tidal force potential was rising again. A significance test supports the hypothesis that the thermal anomalies are physically related to Ludian earthquakes rather than being coincidences. Based on these results, we argue that the change of air temperature could reflect the stress changes modulated under the tidal force. Moreover, unlike the thermal infrared remote sensing data, the air temperature data provided by NCEP are not affected by clouds, so it has a clear advantage for monitoring the pre-earthquake temperature variation in cloudy areas.

Using the air temperature data of the National Center for Environmental Prediction (NCEP), we compared multiple layers of air temperature differences before, during and after the Jiujiang earthquake, and explored its relationship with the additive tectonic stress caused by celestial tide-generating force (ATSCTF). The earthquake occurred at the 1 of 4 high phases of ATSCTF, while the temperature rise came from land surface to high sky. It indicated that the tide force could trigger an earthquake when the tectonic stress was in critical status, and the air temperature rise reflected the terra stress change modulated under the tidal force. During the shock period of ATSCTF, the distribution of air temperature changes both near land surfaces and upper multi-layers along the active fault zones showed a tectonic disturbance pattern of calm before earthquake, rise during earthquake, calm after earthquake as well as a heat distribution pattern of the surface air warmed by land, uplifted by heat flux, cooled and dissipated in the sky. The pattern of changes obeyed the rule of thermal rise of rocks broken under stress loading and the principle of atmospheric thermal dynamic diffusion in vertical. We argued that an earthquake may also be a reason for air temperature differences rather than a simple weather process. At the same time, the rise of air temperature was synchronized with the ATSCTF fluctuant, which showed that tidal force had a particular indicative significance for the identification of temperature anomaly on seismic faults. Because of the mechanical characteristics of the study of earthquake thermal anomalies, it could help to identify the earthquake thermal anomalies and the climatic thermal anomalies, and provided a clear time-indication for the choice of the background temperature in the seismic thermal anomaly recognition. [ABSTRACT FROM AUTHOR]

The Firefly algorithm is a population-based optimization algorithm. It has become popular in the field of optimization and has been applied to engineering practices. Recent works have failed to address how to find the global minimum because their algorithm was trapped in the local minimum. Also, they were not able to provide a balance between exploration and exploitation. In this paper, the Tidal Force formula has been applied to modify the Firefly algorithm, which describes the effect of a massive body that gravitationally affects another massive body. The proposed algorithm brings a new strategy into the optimization field. It is applied by using exploitation (Tidal Force) and keeping a balance between the exploration and exploitation on function suitability. Plate shaped, Steep Ridges, Unimodal and Multimodal benchmark functions were used to compare experimental results. The study findings indicate that the Tidal Force Firefly algorithm outperforms the other existing modified Firefly algorithms. [ABSTRACT FROM AUTHOR]