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GPS network called GEONET (GPS Earth Observation Network system) operated by GSI (Geographical Survey Institute), and he examined the residuals after subtracting the model tides computed by a GOTIC2 program developed by Matsumoto et al. (2001). In this program, 1066A Earth model and NAO.99b ocean tide model are used to compute the body and ocean loading tides. The obtained M 2 residuals for the vertical tidal displacement indicate that their averaged phase difference is 0.11 degrees across the Japanese islands and most of the sites show a phase delay with respect to the predicted tide. More over, the averaged amplitude ratio of the observation to the prediction is 1.007. From these, he concludes that it may show an Earth’s compliant against the response of the Earth obtained from the model computation. Related to this, it may be noted that the 1066A earth model used in GOTIC2 has a soft upper layer compared with other earth models such as PREM model. Although we should carefully test other models for both the body tide and the OTL effects and check the accuracy of the global ocean tide models, there is a possibility that, from this kind of study, we may reveal the departure of the tidal response of the Earth from that expected from the layered Earth, which is shown for instance by the theoretical estimation by Wang (1991). Related to this topic, seismic tomography models have revealed the precise 3D image of the Earth’s interior. Based on the constructed tomography models, a new image of the mantle dynamics such as mantle plume rising up from the core-mantle boundary is proposed. Basically tomography models are constructed from the body and surface wave data such as travel times and waveforms. However, these data have a defect in the sensitivity to density variations, because the density is a common parameter for both of the P- and S-wave velocities. More over, it is known that the density variations estimated by scaling seismic wave speed models may not be accurate. To figure out more reliable 3D structure of the Earth’s mantle including that of the density, two different kinds of approaches are noticed. One is the utilization of lowest frequency data of the free oscillations of the Earth so called ‘gravest seismic normal modes’, which depend on lateral variations in density as well as elasticity, because the gravitational restoring force plays an important role to the amplitude and the frequency splitting of these normal modes (e.g. Ritzwoller Lavely, 1995, Widmer-Schnidrig, 2003, Rosat et al., 2005, 2007). Other is the utilization of the forced oscillations of the Earth such as in the solid Earth tides, because the inside the Earth is deformed by the tidal force as well as its surface, therefore, study of the tidal response of the Earth may be an useful way to reveal in detail about the structure of Earth’s inner including the 3D distribution of the density. Such study has been tried by a group of seismologists of America and Canada (Ishii et al., 2008). 11758
An important issue in the tidal tomography is how we can accurately evaluate a possible systematic error in the estimation of the OTL effects and that due to the effect of spatial distribution of the observation sites which are biased toward the continental land areas on the globe. Anyway, improving the ocean tide models of both the global and regional scales is essential to obtain the reliable image of the 3D structure of inside of the Earth from the tidal observations. But, at least, it can be said that the tidal study is coming to a new stage and its importance increases in the study for the Earth’s 3D model constructions and related geosciences based on these models. 11759
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Page 6 and 7: BIM 146 December 15, 2010 New Chall
Page 8 and 9: 1994), and TPXO.6 (Egbert et al., 1
Page 10 and 11: 4. An attempt to improve the region
Page 12 and 13: From Fig. 2, we also see that, the
Page 16 and 17: References Bos, M. S., Baker, T. F.
Page 18 and 19: Planets Space, 59, 307-311. Sato, T
Page 20 and 21: Fig. 1. Locations of the observatio
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Page 24 and 25: the dense seismic observation netwo
Page 26 and 27: difference of loading effects of oc
Page 28 and 29: is done with an optical lever using
Page 30 and 31: 6. Application of laser interferome
Page 32 and 33: Figure 11. Strain seismograms of th
Page 34 and 35: Higashi, T., 1996, A study on chara
Page 38 and 39: 2. Fundamentals and techniques At t
Page 40 and 41: 100 low frequencies earth tide freq
Page 42 and 43: Tab. 4: Averages of noise levels at
Page 44 and 45: References Asch, G., Elstner, C., J
Page 46 and 47: The 1 / s part is also worth mentio
Page 48 and 49: As it was mentioned before the resu
Page 50 and 51: Fig. 9. Morlet Wavelet Spectrum, su
Page 52 and 53: 9. CONCLUSIONS This investigation w
Page 54 and 55: 2. Objectives of Aswan Tidal Gravit
Page 56 and 57: 5. Recording of Data The data logge
Page 58 and 59: Figure 5: Pre-processed hourly data
Page 60 and 61: Figure 6: Residuals of gravity tide
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time. In addition, models for gravi
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Fig. 3 (Zahran, 2005) shows gravity
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during the years 2003 and 2004. It
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Figure 7: Variation of phase shift,
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Figure 8: Induced gravity load and
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The instrumentation of the tidal st
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4. Tidal analysis The tidal analysi
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References Banka, D., Crossley, D.
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1. Introduction The estimation of a
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Figure 1 Air density distributions
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temperature effect is considered, t
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Figure 4 Attraction effect from the
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a ) up to 0.5° , b) 0.5°- 1.5° ,
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Figure 7 Atmospheric reductions for
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Figure 9 Amplitude spectra of diffe
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Figure 10 SG observation and gravit
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eduction in the long-period tides r
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oceans. The effect has a peak-to-pe
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Figure 1. Local earthquakes recorde
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4. Recording of Data The recorded d
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Table 1: Adjusted tidal parameters
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Acknowledgements: The authors are i
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