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Haruo Sato - One of the best experts on this subject based on the ideXlab platform.
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evidence for tidal triggering of Earthquakes as revealed from statistical analysis of global data
Journal of Geophysical Research, 2002Co-Authors: Sachiko Tanaka, Masakazu Ohtake, Haruo SatoAbstract:[1] We observe tidal triggering of Earthquakes by measuring the correlation between the Earth Tide and Earthquake occurrence. We used the times, locations, and focal mechanisms of the 9350 globally distributed Earthquakes with magnitude 5.5 or larger from the Harvard centroid moment tensor catalog. The tidal stress was theoretically computed by using the Preliminary Reference Earth Model and a recent ocean Tide model, NAO.99b. We considered the shear stress on the fault plane and the trace of stress tensor, J1. Defining the tidal phase angle at the occurrence time for each Earthquake, we statistically tested the phase selectivity using the Schuster's method. For all the Earthquakes, no significant correlation is found between the Earth Tide and Earthquake occurrence both for the shear stress and for J1. By classifying the data set according to fault types, however, we find a high correlation with the shear stress for reverse fault type. The correlation is particularly clear for shallow and smaller Earthquakes of this type. Significant correlation with J1 also appears for larger Earthquakes of reverse fault type and for shallow and larger ones of normal fault type. We find no correlation for strike-slip type. For all the cases of high correlation, Earthquakes tend to occur when the tidal stress accelerates the fault slip, indicating that high correlation is not coincidental but is physically justified. This result strongly suggests that a small stress change due to the Earth Tide encourages Earthquake occurrence when the stress in the future focal area is near a critical condition.
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statistical test of the tidal triggering of Earthquakes contribution of the ocean Tide loading effect
Geophysical Journal International, 1995Co-Authors: Hiroshi Tsuruoka, Masakazu Ohtake, Haruo SatoAbstract:SUMMARY The possibility of tidal triggering of Earthquakes is investigated for a data set that contains 988 globally distributed Earthquakes with magnitude of 6.0 or larger. We synthesize the theoretical time history of tidal stress change, including both solid Earth Tide and ocean Tide loading, at the Earthquake hypocentre, and assign the phase angle of tidal stress at the occurrence time of each Earthquake. The stress due to ocean loading is obtained by convolving the global ocean Tide distribution by Schwiderski with the Green's functions for surface point-mass load, which were newly computed for the Preliminary Earth Model of Dziewonski & Anderson. By testing the distribution of the phase angle statistically, we found a significant phase selectivity for normal-fault-type Earthquakes; the null hypothesis that Earthquakes take place randomly irrespective of the phase angle is rejected at the significance level of 0.54 per cent for the cubic stress component (trace of the tidal stress tensor), and 0.58 per cent for the stress component along the tension axis of the Earthquake's focal mechanism. The highest population of normal-fault-type Earthquakes appears at the time of maximum extensional stress, implying that a decrease in the confining pressure due to the Earth Tide is responsible for triggering Earthquake occurrence. Such a clear phase selectivity is not seen for strike-slip- and thrust-type Earthquakes. The fault-type dependence of the Earthquake triggering effect suggests that shear stress change on the fault plane is also an essential factor of tidal triggering of Earthquakes.
Sachiko Tanaka - One of the best experts on this subject based on the ideXlab platform.
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seismic velocity changes caused by the Earth Tide ambient noise correlation analyses of small array data
Geophysical Research Letters, 2014Co-Authors: Tomoya Takano, Takeshi Nishimura, Hisashi Nakahara, Yusaku Ohta, Sachiko TanakaAbstract:We examine seismic velocity changes due to the Earth Tide by conducting cross-correlation function (CCF) analyses of ambient seismic noise recorded at a small array composed of seven seismometers in northeastern Japan. We calculate CCFs for the dilatational and contractional episodes that are predicted from theoretical tidal volumetric strains. CCFs of the two episodes are highly correlated, but tiny differences are found in their phases. The phase differences are explained by seismic velocity changes of −0.19 ± 0.06% at 1–2 Hz, which are interpreted to be caused by opening/closure of cracks or pores in the shallow subsurface due to the tidal strain. Strain sensitivities of the seismic velocity changes are estimated to be 6.9 × 104 strain−1, which are almost consistent with those reported in previous studies using artificial sources.
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evidence for tidal triggering of Earthquakes as revealed from statistical analysis of global data
Journal of Geophysical Research, 2002Co-Authors: Sachiko Tanaka, Masakazu Ohtake, Haruo SatoAbstract:[1] We observe tidal triggering of Earthquakes by measuring the correlation between the Earth Tide and Earthquake occurrence. We used the times, locations, and focal mechanisms of the 9350 globally distributed Earthquakes with magnitude 5.5 or larger from the Harvard centroid moment tensor catalog. The tidal stress was theoretically computed by using the Preliminary Reference Earth Model and a recent ocean Tide model, NAO.99b. We considered the shear stress on the fault plane and the trace of stress tensor, J1. Defining the tidal phase angle at the occurrence time for each Earthquake, we statistically tested the phase selectivity using the Schuster's method. For all the Earthquakes, no significant correlation is found between the Earth Tide and Earthquake occurrence both for the shear stress and for J1. By classifying the data set according to fault types, however, we find a high correlation with the shear stress for reverse fault type. The correlation is particularly clear for shallow and smaller Earthquakes of this type. Significant correlation with J1 also appears for larger Earthquakes of reverse fault type and for shallow and larger ones of normal fault type. We find no correlation for strike-slip type. For all the cases of high correlation, Earthquakes tend to occur when the tidal stress accelerates the fault slip, indicating that high correlation is not coincidental but is physically justified. This result strongly suggests that a small stress change due to the Earth Tide encourages Earthquake occurrence when the stress in the future focal area is near a critical condition.
R. Ian Acworth - One of the best experts on this subject based on the ideXlab platform.
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Technical Note: Disentangling the groundwater response to Earthand atmospheric Tides to improve subsurface characterisation
2020Co-Authors: Gabriel C. Rau, R. Ian Acworth, Mark O. Cuthbert, Philipp BlumAbstract:Abstract. The groundwater response to Earth Tides and atmospheric pressure changes can be used to understand subsurface processes and estimate hydraulic and hydro-mechanical properties. We develop a generalised frequency domain approach to disentangle the impacts of Earth and atmospheric Tides on groundwater level responses. By considering the complex harmonic properties of the signal, we improve upon a previous method for estimating barometric efficiency (BE) estimation while simultaneously assessing system confinement and estimating hydraulic conductivity as well as specific storage. We demonstrate and validate the novel approach using an example barometric and groundwater pressure record with strong Earth Tide influences. Our method enables improved and rapid assessment of subsurface processes and properties using standard pressure measurements.
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calculation of barometric efficiency in shallow piezometers using water levels atmospheric and Earth Tide data
Hydrogeology Journal, 2008Co-Authors: R. Ian AcworthAbstract:The variation in atmospheric pressure at Baldry in New South Wales, Australia (32°52′ S, 148°32′ E), has been determined using a 4-year record of hourly measurements. Fourier analysis of this data shows clear diurnal and semi-diurnal variation in atmospheric pressure caused by atmospheric Tides. The semi-diurnal component of the Tide changes little with the seasons and induces a barometric response in shallow confined piezometers. The piezometer response is shown to be contaminated by an Earth-Tide component that has to be removed before accurate barometric efficiencies can be calculated. Data from three piezometers installed in a region of fractured and weathered granite are described in this paper. The results show that piezometers installed in shallow bedrock can have barometric efficiencies of close to unity and that only a small quantity or thickness of lower permeability material is sufficient to cause confining conditions. This observation has important implications for the interpretation of recharge processes in shallow aquifers.
Hans-georg Scherneck - One of the best experts on this subject based on the ideXlab platform.
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a parametrized solid Earth Tide model and ocean Tide loading effects for global geodetic baseline measurements
Geophysical Journal International, 1991Co-Authors: Hans-georg ScherneckAbstract:SUMMARY An observation model for Earth Tide displacements in application to Very Long Baseline Interferometry and similar precise geodetic techniques is developed. It incorporates effects from anelasticity, ellipsoidal figure, and fluid core resonance. Based on a harmonic development of the external potential, the model follows the familiar Love number concept. The transfer function of the Earth to each harmonic is formulated in terms of coupled harmonics in the space domain and fulfils the causality condition in the time domain. Solve-for parameters can be chosen flexibly. The guideline, however, has been to provide a minimum set of well-defined and well-resolvable Tide response parameters for analysis of observations. The aim of accuracy for Tide displacements prediction is below 1 mm. Being the major perturbation of the solid Earth Tide, ocean Tide loading effects are computed, and the accuracy of the models involved is discussed. It appears that the major error source relates to those ocean Tide frequencies for which global models are not available. These frequencies form a continuum with a power spectrum being largely a result of non-linear Tide interaction. The associated loading effects cannot be reliably interpolated from global Tide models, which are available only for a few distinct frequencies and which disregard tidal intermodulation. Thus, an accuracy of 1 mm for computed loading Tide displacements cannot always be achieved.
H G Wenzel - One of the best experts on this subject based on the ideXlab platform.
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analysis of Earth Tide observations
Lecture Notes in Earth Sciences Berlin Springer Verlag, 1997Co-Authors: H G WenzelAbstract:We will give in the following a short description of the analysis of Earth Tide observations. Earth Tide analysis is usually carried out in order to estimate the frequency transfer function of the system Earth — station — sensor, where the parameters of the transfer function (i.e. the tidal parameters) are determined from a least squares adjustment of the Earth Tide observations. We will describe the mathematical model of the Earth Tide analysis program ANALYZE (Wenzel, 1996a,b) and we will give two examples.
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the harmonic development of the Earth Tide generating potential due to the direct effect of the planets
Geophysical Research Letters, 1994Co-Authors: Torsten Hartmann, H G WenzelAbstract:The time-harmonic development of the Earth Tide generating potential due to the direct effect of the planets Venus, Jupiter, Mars, Mercury and Saturn has been computed. The catalogue of the fully normalized potential coeffients contains 1483 waves. It is based on the DE102 numerical ephemeris of the planets between years 1900 and 2200. Gravity Tides due to the planets computed from the catalogue at the surface of the Earth have an accuracy of about 0.027 pm/s² (1 pm/s² = 10−12 m/s² = 0.1 ngal) rms and 0.160 / 0.008 pm/s² at maximum in time / frequency domain using the new benchmark tidal gravity series (Wenzel 1994).
