Effects Of Earth Tides Research Articles

Newtonian (moving mass) calibration of tilt and gravity meters and the investigation of some factors influencing its accuracy

The idea of moving mass calibration (MMC) of relative gravity meters dates back to the seventies of the last century. Probably the MMC apparatus built in the underground Mátyáshegy Gravity and Geodynamics Laboratory Budapest has been used most extensively and several spring type instruments (LaCoste and Romberg and Scintrex) have been investigated and calibrated by it. Its test mass is a cylindrical ring having a weight of 3 tons. Its main advantage is simplicity in terms of metrology. The same principle and technology can be used to test compact tilt sensors having nanoradian resolution capability. Up to now rigorous testing methods below microradian range were not available in practice. The analysis of the so-called off-axis variation of the gravitational vector generated by the vertical movement of the cylindrical ring mass of the Mátyáshegy MMC device, however, showed that a sufficiently accurate reference signal having (15 ± 0.02) nrad peak-to-peak amplitude can be provided for calibration. It is just in the range of tilt induced by earth tide effect, which is a “standard” signal component in the time series recorded in observatory environment. In the first part of the paper, a discussion of the proposed methodology of tilt meter calibration is given. Then the analysis of the effect of volumetric discretization of the cylindrical ring on the accuracy of calibration is provided. Finally, possible material inhomogeneities of the ring mass and their gravitational effects are investigated by forward simulations and inversion. For this purpose the results of 300 gravimeter calibration experiments, analysed and published earlier, were utilized.

Groundwater Responses to Earth Tides: Evaluation of Analytical Solutions Using Numerical Simulation

AbstractHarmonic Earth tide components in well water levels have been used to estimate hydraulic and geomechanical subsurface properties. However, the robustness of various methods based on analytical solutions has not been established. First, we review the theory and examine the latest analytical solution used to relate well water levels to Earth tides. Second, we develop and verify a novel numerical model coupling hydraulics and geomechanics to Earth tide strains. Third, we assess subsurface conditions over depth for a range of realistic properties. Fourth, we simulate the well water level response to Earth tide strains within a 2D poroelastic layered aquifer system confined by a 100 m thick aquitard. We find that the non‐linear inversion of analytical solutions to match two observations (amplitudes and phases) to multiple unknown parameters is sensible to the initial guess. We reveal that undrained, confined conditions are necessary for the analytical solution to be valid. This occurs for the dominant M2 frequency at depths >50 m and requires specific storage at constant strain of Sϵ ≥ 10−6 m−1, hydraulic conductivity of the aquitard of kl ≤ 5 ⋅ 10−5 ms−1 and aquifer of ka ≥ 10−4 ms−1. We further illustrate that the analytical solution is valid in unconsolidated systems, whereas consolidated systems require additional consideration of the Biot modulus. Overall, a priori knowledge of the subsurface system supports interpretation of the groundwater response. Our results improve understanding of the effect of Earth tides on groundwater systems and its interpretation for subsurface properties.

К теории детерминированного прогноза землетрясений методом LURR

This paper considers theoretical aspects of a trigger effect of earth tides on earthquake initiation under the LURR approach. The growth of Coulomb stress, which appears resulting from this phenomenon, is shown to occur not for all regimes of stress state acting in the studied region. Its greatest increase corresponds to the regime of the horizontal extension and shear associated with the faults with kinematics of the normal and strike-slip faults. The low level of additional Coulomb stress for the horizontal compression regime allows asserting the low probability of the trigger effect for the faults with kinematics of the reverse faults. It is noted, that there is also an indirect factor in the form of additional pressure caused by the sea tides in addition to the main factor of the earth tides effect on deformations in the solid earth for island arcs and coastal areas of the continental crust. This is an additional vertical pressure for the ocean floor, and a lateral pressure for the crust of island arcs and coastal areas of the continents. Indirect factors significantly complicate the effect of earth tides on the Earth’s crust, completely neutralizing the influence of the direct factor in some cases.

Un modelo de mareas para el Observatorio Argentino-Alemán de Geodesia (AGGO) utilizando observaciones del gravímetro superconductor SG038

El Observatorio Argentino-Alemán de Geodesia (AGGO) es un observatorio fundamental de geodesia ubicado en las cercanías de la ciudad de La Plata, Argentina. AGGO cuenta con las principales técnicas geodésicas espaciales, GNSS, VLBI y SLR. Por otra parte, AGGO posee un Laboratorio de Gravimetría, donde el gravímetro superconductor (SG) SG038 realiza mediciones en forma continua de las variaciones de gravedad, desde diciembre del año 2015. Además, el gravímetro absoluto FG5-227 provee un valor de gravedad absoluto de referencia para AGGO y para Latinoamérica desde enero del año 2018. En este trabajo se presenta un modelo de mareas obtenido a partir del análisis de tres años de observaciones del SG. Los SGs son capaces de medir variaciones de la gravedad en un gran espectro de amplitudes y frecuencias, desde mareas terrestres hasta efectos hidrológicos. Para analizar distintos efectos en las observaciones de un SG, primero debe realizarse un cuidadoso tratamiento de la señal observada. Para esto se obtuvieron los residuos preliminares, luego de eliminar las principales fuentes de variaciones de gravedad. Saltos y picos ocasionados por terremotos, cortes de luz, etc., fueron eliminados de la señal residual y a su vez filtrada, obteniendo una señal suave y continua. Luego, las señales de mareas terrestres y carga oceánica fueron restituidas a la señal residual. El procesamiento de la señal resultante se realizó con la última versión del software ETERNA ETA34-X, incluyendo el grado 3 del potencial de marea de ciertas ondas de marea en el análisis de marea. Como resultado del análisis de tres años de observaciones, se obtuvieron los parámetros de marea de 55 grupos de onda. En segundo lugar, se ha analizado el impacto de distintos modelos de marea oceánica en los parámetros, con el fin de separar los efectos de marea terrestre y carga oceánica

ARTIFICIAL INTELLIGENCE TECHNIQUES FOR PREDICTING TIDAL EFFECTS BASED ON GEOGRAPHIC LOCATIONS IN GHANA

Tidal forces as a result of attraction of external bodies (Sun, Moon and Stars) through gravity and are a source of noise in many geoscientific field observations. The solid earth tides cause deformation. This deformation results in displacement in geographic positions on the surface of the earth. The displacement due to tidal effects can result in deformation of engineering structures, loss of lives, and economic cost. Tidal forces also help in detecting other environmental and tectonic signals. This study quantifies the effects of solid earth tides on stationary survey controls in five regions of Ghana. The study is in two stages: firstly, the solid earth tides were estimated for each control by a geometric approach (combining Navier’s equation of motion and Love theories). Secondly, estimation using two artificial intelligence methods (Multivariate Adaptive Regression Splines (MARS) and Backpropagation Artificial Neural Network (ANN)). Based on statistical indices of Mean Square Error (MSE) and Correlation Coefficient (R), BPANN, and MARS models can be used as a realistic alternative technique in quantifying solid earth tides for the study area. The MSE and R (MSE; BPANN = 1.3249 × 10–04 and MSE; MARS = 2.2052 × 10–06; R; BPANN = –0.6067 and R; MARS 0.6570) values indicate that MARS outperforms BPANN in quantifying solid earth tides in the study area. BPANN and MARS can be used as an efficient tool for quantifying tidal values based on geographic positions for geodetic deformation studies within the study area.

Spatiotemporal Ocean Tidal Loading in InSAR Measurements Determined by Kinematic PPP Solutions of a Regional GPS Network

The coastal crustal deformation caused by ocean tidal loading (OTL) varies spatially and temporally, and this spatiotemporal variation in satellite-based interferometric synthetic aperture radar (InSAR) measurements needs to be determined. In this article, we propose a spatiotemporal modeling method to estimate the OTL displacements in InSAR measurements using the kinematic precise point positioning (PPP) solutions of a regional GPS network. We tested the method through an experiment using 25 Sentinel-1B images and long-term observations of 172 GPS reference sites from Southern California. The experimental results suggest that there are significant OTL and solid Earth tide effects in the differential InSAR interferogram, which is greater than 40 mm. We find that the spatial characteristics of OTL variations can be expressed as a high-order polynomial in the two variables of latitude and longitude, and the spatiotemporally modeled PPP tidal estimates of the high-density GPS sites can provide high precision OTL correction for all the pixels in the interferogram. In the last part of the study, we show that the spatial large-scale signals in the differential interferograms of Sentinel-1B data are mainly atmospheric delay, solid Earth tidal, and OTL effect, and demonstrate the importance of the tidal correction in the InSAR measurements.

Factors influencing hydrogen flux in a fault zone of Henan Province, China

This research investigates the main factors influencing changes in hydrogen concentration in a fault zone and analyzes the relationship between hydrogen and tectonic activity. Based on the hydrogen concentration in the fault gas and continuous observation data from Mashankou, Neixiang County, Henan Province, the relationships between the variation in hydrogen concentration and ground temperature, atmospheric temperature, and atmospheric pressure are analyzed. In addition, the earth tide effect on hydrogen in the fault zone is discussed. The results show that the direct influence of atmospheric or ground temperatures on the hydrogen concentration is not significant. The atmospheric and ground temperatures have some impact on the hydrogen concentration only when ground temperature increases. By means of a wavelet analysis method, which separates the semidiurnal wave and diurnal wave signals of hydrogen, the results show that the hydrogen concentration is capable of indicating the solid earth tide when comparing the pressure tide and solid earth tide signals in the same period.

Review: Moisture loading—the hidden information in groundwater observation well records

Changes of total moisture mass above an aquifer such as snow accumulation, soil moisture, and storage at the water table, represent changes of mechanical load acting on the aquifer. The resulting moisture-loading effects occur in all observation well records for confined aquifers. Deep observation wells therefore act as large-scale geological weighing lysimeters, referred to as “geolysimeters”. Barometric pressure effects on groundwater levels are a similar response to surface loading and are familiar to every hydrogeologist dealing with the “barometric efficiency” of observation wells. Moisture-loading effects are small and generally not recognized because they are obscured by hydraulic head fluctuations due to other causes, primarily barometric pressure changes. For semiconfined aquifers, long-term moisture-loading effects may be dissipated and obscured by transient flow through overlying aquitards. Removal of barometric and earth tide effects from observation well records allows identification of moisture loading and comparison with hydrological observations, and also comparison with the results of numerical models that can account for transient groundwater flow.

Constraints on density changes in the funnel-shaped caldera inferred from gravity monitoring of the Lusi mud eruption

From its inception May 29, 2006, the Lusi mud eruption has continuously erupted fluids, boiling mud and clasts through large active vents approximately 100 m in diameter. In 2016, we conducted a Dynamic Gravity survey (DG) using a network built over four locations and two Continuous Gravity-monitoring (CG) experiments to monitor the eruption activity. The CG was done for 8 days from June 2nd to June 10th, and for 9 days from August 20th to August 29th, 2016. Atmospheric pressure and atmospheric temperature variations were recorded during each experiment to constrain potential environmental effects, and Earth and oceanic tide effects were removed from gravity signals (CG and DG). Atmospheric pressure effects were removed from CG gravity signals. At the station, closest to the hydrothermal pond, the DG survey results show a gravity increase of ∼0.009 mGal month−1, which we interpret as the growth of the mud edifice in the central area. CG-monitoring shows that gravity variations occur at a period of 12–13 h, with amplitudes reaching up to 0.020 mGal. We interpret this as relating to density variation of the rising mud mixture (fluids + coarse mud + clasts). The observed 12–13 h period variations appear to indicate that tides may have some control on the density change of rising mud mixture by triggering the release of gas trapped at depth. Our 3D gravity results around the Lusi vents show that density variations range from 100 kg m−3 to 775 kg m−3. Similarly, vent diameters better constrain density contrasts occurring within the caldera zone, which is more likely to range between 400 and 450 kg m−3, and is equivalent respectively to 27% and 31% of gas ratio change over time.

Research Article. Towards a tidal loading model for the Argentine-German Geodetic Observatory (La Plata)

Abstract We present a regionalized model of ocean tidal loading effects for the Argentine-German Geodetic Observatory in La Plata. It provides the amplitudes and phases of gravity variations and vertical deformation for nine tidal constituents to be applied as corrections to the observatory’s future geodetic observation data. This model combines a global ocean tide model with a model of the tides in the Río de la Plata estuary. A comparison with conventional predictions based only on the global ocean tide model reveals the importance of the incorporation of the regional tide model. Tidal loading at the observatory is dominated by the tides in the Atlantic Ocean. An additional contribution of local tidal loading in channels and groundwater is examined. The magnitude of the tidal loading is also reviewed in the context of the effects of solid earth tides, atmospheric loading and non-tidal loads.

Characterizations of geothermal springs along the Moxi deep fault in the western Sichuan plateau, China

Abundant geothermal springs occur along the Moxi fault located in western Sichuan Province (the eastern edge of the Qinghai-Tibet plateau), highlighted by geothermal water outflow with an unusually high temperature of 218°C at 21.5MPa from a 2010-m borehole in Laoyulin, Kangding. Earthquake activity occurs relatively more frequently in the region and is considered to be related to the strong hydrothermal activity. Geothermal waters hosted by a deep fault may provide evidence regarding the deep underground; their aqueous chemistry and isotopic information can indicate the mechanism of thermal springs. Cyclical variations of geothermal water outflows are thought to work under the effect of solid earth tides and can contribute to understanding conditions and processes in underground geo-environments. This paper studies the origin and variations of the geothermal spring group controlled by the Moxi fault and discusses conditions in the deep ground. Flow variation monitoring of a series of parameters was performed to study the geothermal responses to solid tides. Geothermal reservoir temperatures are evaluated with Na-K-Mg data. The abundant sulfite content, dissolved oxygen (DO) and oxidation-reduction potential (ORP) data are discussed to study the oxidation-reduction states. Strontium isotopes are used to trace the water source. The results demonstrate that geothermal water could flow quickly through the Moxi fault the depth of the geothermal reservoir influences the thermal reservoir temperature, where supercritical hot water is mixed with circulating groundwater and can reach 380°C. To the southward along the fault, the circulation of geothermal waters becomes shallower, and the waters may have reacted with metamorphic rock to some extent. Our results provide a conceptual deep heat source model for geothermal flow and the reservoir characteristics of the Moxi fault and indicate that the faulting may well connect the deep heat source to shallower depths. The approach of hot spring variation research also has potential benefits for earthquake monitoring and prediction.

Review of the lunar laser ranging technique and contribution of timing systems

The lunar laser ranging (LLR) technique is based on the two-way time-of-flight of laser pulses from an earth station to the retroreflectors that are located on the surface of the moon. We discuss the ranging technique and contribution of the timing systems and its significance in light of the new LLR station currently under development by the Hartebeesthoek Radio Astronomy Observatory (HartRAO). Firstly, developing the LLR station at HartRAO is an initiative that will improve the current geometrical network of the LLR stations which are presently concentrated in the northern hemisphere. Secondly, data products derived from the LLR experiments – such as accurate lunar orbit, tests of the general relativity theory, earth–moon dynamics, interior structure of the moon, reference frames, and station position and velocities – are important in better understanding the earth–moon system. We highlight factors affecting the measured range bias such as the effect of earth tides on station position and delays induced by timing systems, as these must be taken into account during the development of the LLR analysis software. HartRAO is collocated with other fundamental space geodetic techniques which makes it a true fiducial geodetic site in the southern hemisphere and a central point for further development of space-based techniques in Africa. Furthermore, the new LLR will complement the existing techniques by providing new niche areas of research both in Africa and internationally.

A series expansion of the solid Earth tide effect on geopotential

We develop analytical series representing the main part of corrections to the geopotential coefficients caused by the solid Earth tides, where Love numbers are assumed to be frequency-independent. The series are compact, precise and valid over 1800 A.D.–2200 A.D. The maximum difference between the corrections given by the analytical series and their numerical values, obtained with use of the DE/LE-423 planetary/lunar ephemerides, does not exceed \(0.7\times 10^{-12}\). A new algorithm is proposed for calculating amplitudes of the additional variations of the geopotential coefficients for frequency dependence of Love numbers. It uses the representation of the Earth tide-generating potential in the standard HW95 format and takes into account the phase of tidal waves. Corrections of up to \(2\times 10^{-12}\) to the published by the IERS Conventions (2010) amplitudes of the additional variations of the geopotential coefficients are suggested. Examples of use of the obtained series in analytical theories of motion of low-altitude STARLETTE and high-altitude ETALON-1 satellites are given.

Ground Displacement Measurement by TerraSAR-X Image Correlation: The 2011 Tohoku-Oki Earthquake

Japan was struck by an M9.0 megathrust earthquake on March 11, 2011. Synthetic aperture radar (SAR) images from the TerraSAR-X satellite have been used to generate a ground motion map by means of correlation techniques. Geophysical corrections due to solid Earth tide and atmospheric path delay effects have been applied. These corrections can reach up to 20 cm in the radar line of sight. Using this approach, absolute displacements in the radar line of sight and in the satellite flight direction are determined. This letter shows the potential of correlation techniques for ground motion monitoring and a comparison with the interferometric technique. Using multiple scenes, a wide area displacement map is generated and quantitatively compared with GPS data, showing a divergence of about 15 cm.

Benford’s Law in Time Series Analysis of Seismic Clusters

Benford’s analysis is applied to the recurrence times of approximately 17,000 seismic events in different geological contexts of Italy over the last 6 years, including the Mt. Etna volcanic area and the seismic series associated with the destructive Mw 6.3, 2009 L’Aquila earthquake. A close conformity to Benford’s law and a power-law probability distribution for the recurrence times of consecutive events is found, as typical of random multiplicative processes. The application of Benford’s law to the recurrence event times in seismic series of specific seismogenic regions represents a novel approach, which enlarges the occurrence and relevance of Benford-like asymmetries, with implications on the physics of natural systems approaching a power law behaviour. Moreover, we propose that the shift from a close conformity of Benford’s law to Brownian dynamics, observed for time separations among non-consecutive events in the study seismic series, may be ruled by a periodical noise factor, such as the effects of Earth tides on seismicity tuning.

An approach to the validation of thermal and electromagnetic earthquake precursors: Effects of earth tides

It has been debated for years whether earth tides trigger earthquakes. A recent statistical study has proven the significance of earth tides in earthquake triggering. In this paper, we firstly show that large earthquakes in the region of the 2004 Sumatra earthquake (M9.0) occur largely during a specific phase of the Moon. Then, we show that the observed thermal/electromagnetic precursors of the outgoing long wave earth radiation and the VLF propagation anomaly (ionospheric perturbation) at the time of an earthquake are modulated by the tidal effect of the region. Finally, we propose a model to explain the observed behaviors of the thermal/electromagnetic precursors, and show that tidal stress can trigger earthquakes, leading also to thermal/electromagnetic signatures.

The effect of earth tides as observed in seismo-electromagnetic precursory signals

Abstract. Studies on the effect of earth tides in triggering earthquakes (EQs) had a great progress in recent years, which has provided convincing evidence of earth tides in EQ triggering. On the other hand, there have been accumulated a lot of evidences on the presence of seismogenic electromagnetic effects (such as ULF electromagnetic emissions from the lithosphere, ionospheric perturbations as detected by subionospheric VLF/LF propagation, etc.). Since the initial agent of these seismogenic electromagnetic effects is obviously due to some mechanical action around the EQ focal zone, the tidal effect as seen in EQ sequence should appear also in seismo-electromagnetic phenomena. Based on this expectation we have studied the tidal effect in different seismogenic phenomena, and have found that lithospheric ULF emissions exhibit a clear maximum-minimum-maximum pattern synchronized with the lunar phase of the EQ during several months before the EQ. As for VLF/LF propagation anomaly representing the lower ionospheric perturbation, we have found the tidal modulation very similar to ULF emissions, but less clear, and also there are some differences from the ULF case (such as occasional shift with respect to the lunar phase and/or the presence of higher frequency modulation, etc.). These findings are indicative that those electromagnetic phenomena reported to be in possible association with an EQ are really related with any preparatory phase of an EQ. This kind of study would be a bridge between the seismology and our seismo-electromagnetic study.

Time series of superconducting gravimeters and water storage variations from the global hydrology model WGHM

The gravimetric time series achieved from the combination of superconducting and absolute gravimeters are characterized by highest precision and long-term stability. If the effects of Earth and ocean tides, atmosphere and polar motion are removed, the residual curve is dominated by hydrological mass variations. A major source of these variations is water storage changes in the vicinity of the sensor. However, global variations contribute to the signal significantly. For three stations of superconducting gravimeters, a comparison of the principal components obtained from the residual gravity curve on the one hand and continental water storage from the WaterGAP Global Hydrological Model (WGHM) on the other hand is carried out. The results demonstrate a coherence of seasonal variations but a difference in the contribution of the local zone at the individual stations, which point out the need for a careful and site-specific examination of local effects.

Systematic examination of ‘precursor waves’ of strong earthquakes by using the wavelet method

Based on the borehole strainmeter recordings immediately before the strong earthquakes (MS≥7.5) during the period from 2001 to 2005 observed at the Taian observation station, Shandong Province, the authors make a systematic and objective examination of the precursor waves of the quakes. The effects of Earth tides with periods larger than 128 min are eliminated through high-pass filtering; and atmospheric-pressure inferences are removed by linear regression. The 2–128 min signals are then separated into six frequency bands by employing the wavelet method. Results indicate that the wavelet method is capable of picking out information of weak variations in the signals. According to the characteristics of the ‘precursor waves’ obtained from wavelet transformation, the method of overrun ratio analysis is put forward for examination. All the detailed components of the wavelets have been analyzed. For the time series of the overrun rate in all these components, statisitical calculation has been made for the slopes of fit curves, and mean values and standard deviations were obtained and positive-negative slope ratios were analyzed. The three statistical data show that ‘precursor waves’ are not widely recorded by borehole strainmeter within 15 days before remote strong earthquakes.

The effect of earth tides in triggering earthquake as clearly observed in some specific regions of Japan

The question of whether earth tides trigger earthquakes has been the subject of debate for years. Recent studies, at last, have proven the significance of the earth tide effect in triggering earthquakes, and they further reported that the direction of the compressional stress at a region created by the earth tide almost coincides with that of the dominant principal pressure axes of the focal mechanisms at the region. This suggests that there might be specific positions of the Moon, Sun and Earth, known as lunar phases that create effective tidal force for earthquakes at each fault. So that, this paper examines the relationship between earthquakes and the lunar phases in some specific regions of Japan, and the significant effect of earth tide in triggering earthquakes is confirmed.