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Malte Westerhausl, Walter Zürn
2001 年 47 巻 1 号 p.
1-9
発行日: 2001/03/25
公開日: 2010/09/07
ジャーナル
フリー
During the IDNDR decade geodynamic monitoring stations have been installed in many tectonically active areas. The improvement of sensor- and data acquisition techniques considerably broadened the observation of strain induced (tidal) signals, including an increasing number of 'nonclassical' quantities like physico-chemical parameters of ground water or electrical resistivity. As a continuous and well known source of deformation acting on the earth at any place and any time, earth tides provide a unique possibility to validate the coupling of the sensors to the ground, to carry out in situ calibrations and to check the temporal stability of the response characteristics. The response to an imposed tidal strain may provide insight into the physics and the linearity/non-linearity of the strain coupling mechanisms which is important especially for ?enatural' strain sensors like wells and thermal/mineral springs. If the recording system provides calibration facilities, the local tidal response functions may be investigated with respect to changes of mechanical properties of the crust during the preparation of earthquakes and volcanic eruptions.
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Abdelbar El Wahabi, Bernard Ducarme, Michel Van Ruymbeke
2001 年 47 巻 1 号 p.
10-15
発行日: 2001/03/25
公開日: 2010/09/07
ジャーナル
フリー
LaCoste & Romberg (LCR) gravimeters are able to record small non tidal gravity variations for periods ranging from some days to several months if one corrects the instrumental effects due to air temperature and humidity. An experiment has been carried out in five stations using the same gravimeter (the LCR G906) and the temperature effect was established for short and medium periods. At Membach (Belgium), the LCR G906 was installed next to the superconducting gravimeter C021 in very stable conditions of humidity and temperature and after removing a long term drift from the LCR G906 signal, the gravity variations recorded by both instruments agree at the microgal level. In order to reach a similar result with LCR gravimeters in stations where the temperature and humidity are not stable, some experiments were performed in the fundamental station of Brussels in the Royal Observatory of Belgium (ROB) using the LCR G8 to study the meteorological influences. This gravimeter showed a correlation with the humidity signal for periods longer than 10 days. To a humidity step of 35%, it reacted quasi-instantaneously by going steadily up by more than 1.5 milligal in three months and going down similarly while the humidity was returning to normal. We showed that the LCR G8 behaves like an integrator of air humidity changes. With this experiment, we partially met the result of Bastien et al (1990) and we significantly improved the understanding of the behaviour of LCR gravimeters on what concerns the humidity effect. As the reaction of each gravimeter is different, a similar experiment should be performed for each instrument.
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Olivier Francis, Marc Hendrickx
2001 年 47 巻 1 号 p.
16-21
発行日: 2001/03/25
公開日: 2010/09/07
ジャーナル
フリー
Three months of simultaneous and collocated observations by a superconducting and a spring gravimeter in Membach are used to calibrate the spring gravity meter. We show that a precision of 0.1% on the amplitude calibration factor can be achieved with two weeks of data. The time variation of this calibration factor over the three months is found to be less than 0.1%. This is the precision required for our specific application of the spring meter, to validate the ocean tides models along the Atlantic coast. The determination of the instrumental phase lag is not satisfactory. A precision of only a few seconds has been achieved. For phase calibration, other methods are more successful.
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Reinhard Falk, Martina Harnisch, Günter Harnisch, Ilona Nowak, Be ...
2001 年 47 巻 1 号 p.
22-27
発行日: 2001/03/25
公開日: 2010/09/07
ジャーナル
フリー
In the last years the superconducting gravimeters of the Bundesamt fur Kartographie and Geodasie (BKG) have been calibrated several times by comparison with absolute gravity measurements. Averaging over all measuring campaigns, stable results with errors in the order of 1 nm
s-2N are reached. Three of the instruments were also calibrated by the platform method. The internal accuracy of this method is higher by about one order of magnitude. However, there are discrepancies between the results of the two different calibration methods, the origin of which is still not clear.
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Hannu Ruotsalainen
2001 年 47 巻 1 号 p.
28-33
発行日: 2001/03/25
公開日: 2011/07/05
ジャーナル
フリー
The very long water-tube tiltmeter of the Finnish Geodetic Institute is to be modernized with new materials and a new recording system. We shall keep the stable interferometer arm design as it is, following concepts developed earlier at the Finnish Geodetic Institute. The new interferometric recording system will consist of a HeNe laser, fibre optics and a digital PC- camera. The automated interpretation of interference fringes by computer is currently been tested in the laboratory. The pot/interferometer system will be mounted on an adjustable tripod. The pot and the tube are to be built of glass. Special attention is to be paid to matching the tube/fluid thermal expansion and to eliminating corrosion. Slow minute corrosion in the instrument is difficult to detect and therefore the choice of correct material is vital under hostile underground conditions. An optical fluid with appropriate physical properties and compatible with glass would be preferable to water. By using a higher interferometric resolution we shall try to shorten the instrument without losing the high nanoradian tilt resolution and good long-term instrumental stability. A modular design will make it easy to install the tiltmeter in various environments, for different applications in geodynamics.
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Thomas Jahr, Gerhard Jentzsch, Corinna Kroner
2001 年 47 巻 1 号 p.
34-39
発行日: 2001/03/25
公開日: 2010/09/07
ジャーナル
フリー
Since 1997 the seismological station, Moxa, has been reconstructed and extended to become a geodynamic broadband observatory. Seismological observations are carried out with a seismometer STS-2 (3-component) now supplemented with a three component STS-1, a long period seismometer, which usually operates at up to 360 seconds but is also sensitive to tidal signal. The original east west and north-south quartz strainmeters were reconstructed and equipped with new inductive sensor systems. A laser strainmeter, orientated from north-west to south-east, has also been newly installed. The beam runs through a horizontal borehole. All three components show clearly the expected tidal strain variations. Cavity effects seem to be small. In front of the observatory buildings three boreholes, two 50 meter and one 100 meter, were drilled and first test recordings with the ASKANIA borehole tiltmeter were carried out. As an optical estimation of the pendulum azimuth was not possible, a new method was developed by use of seismological observations from well-known locations. Signals and noise recorded by the different sensor systems were investigated in particular not only for seismological frequencies, but also for very long period.
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Michel van Ruymbeke, Francois Beauducel, André Somerhausen
2001 年 47 巻 1 号 p.
40-46
発行日: 2001/03/25
公開日: 2010/09/07
ジャーナル
フリー
Multi-parameters approach is required for the monitoring of complex interactions induced by tectonic activities (volcanic, geothermal and seismic areas, land-slide zones...).The diversity of sensors becomes so broad that the use of existing technology provides a difficult barrier for scientists not familiar with metrology. To address this problem, the Royal Observatory of Belgium develops the Environmental Data Acquisition System EDAS. The core base of this standardised system are the different monitoring devices. They produce data files which follow a standard sequence containing date, time and the recorded values in ASCII columns. Different type of electronic for instruments with resistive and capacitive transducers were designed. They operate using standard supplies. Their output signals are compatible with the data acquisition system. In complement to the EDAS system, a set of applications has been written for the data analysis, known as EDAT, like HiCum software which is tool useful to analyse signatures on special periodicity from graphics obtained with stacking method. The EDAS concept complete tidal probes by improvement of access to various signals susceptible to influence tidal records.
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Nicolas D'Oreyel, Gilbert Klein, Gilles Cellil, Patrick Harpes
2001 年 47 巻 1 号 p.
47-51
発行日: 2001/03/25
公開日: 2010/09/07
ジャーナル
フリー
The "European Center for Geodynamics and Seismology" (EGGS) in cooperation with the "Centre de Recherche Public Henri Tudor" (CRP -HT) has developed a new integrated data acquisition system for the Underground Laboratory of Walferdange in the Grand Duchy of Luxembourg. The system, dubbed WALLACE ("WALferdange Laboratory ACquisition Equipment"), is designed to address the strictest requirements necessary for remotely managing a geophysical laboratory. Although it is still in a developmental stage, the separate modular components have each already been tested in the Underground Laboratory of Walferdange.
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Yuichi Imanishi
2001 年 47 巻 1 号 p.
52-57
発行日: 2001/03/25
公開日: 2010/09/07
ジャーナル
フリー
A GPIB data acquisition system for high-rate and high-resolution sampling of time-varying signals is developed based on the real-time computer operating system RT-Linux. In this system, the real-time process for controlling GPIB devices is triggered by CPU interrupt requests raised by the hardware real-time clock, and is executed with the highest priority among all the processes under the control of the RT-Linux kernel. This mechanism enables stable, continuous, high-rate and high-resolution sampling with microsecond timing accuracy. The system is experimentally applied to superconducting gravimeter observations with very good results. This system provides a solution to the general problem of long-term degradation of the analog antialiasing filters used in many kinds of observations such as superconducting gravimetry.
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大谷 文夫, 寺石 眞弘, 古澤 保, 園田 保美
2001 年 47 巻 1 号 p.
58-63
発行日: 2001/03/25
公開日: 2011/07/05
ジャーナル
フリー
We designed a liquid-tube tiltmeter that is only half-filled with silicon oil. The tiltmeter consists of float and a pair of magnets in each sensing pot. The float has an iron fork at the bottom and a pair of magnets keeps the float at the center of the pot and prevents it from rotation. This instrument was installed next to a normal type water-tube tiltmeter and the results of the tidal analysis of the data from these two types of tiltmeters are compared. The effects of atmospheric pressure have been shown to decrease remarkably in the half-filled type data.
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Michel van Ruymbeke, Bernard Ducarme, Andre Somerhausen
2001 年 47 巻 1 号 p.
64-69
発行日: 2001/03/25
公開日: 2010/09/07
ジャーナル
フリー
A new series of registrations of the gravity tides has been achieved at the Royal Observatory of Belgium with the LaCoste & Romberg Portable Earth-Tides PET1006 which has been calibrated in two different ways. This instrument is equipped with a step motor mounted directly on the axis of the micrometer. It becomes possible to do very precise micrometric calibration to determine the ratio between the micrometer screw rotations and the signal output modulations. The gravimeter was installed on the calibration platform which induces well known sinusoidal inertial accelerations at different periods controlled by a quartz clock. In parallel with the signal produced by the gravimeter, we register a signal coming from a displacement sensor which records the motion of the platform. This sensor has a scale factor referenced to a LASER interferometer. For periods in the range of 200 to 300 seconds, the phase lag between the gravimeter and the displacement sensor is quasi stable around 15 sec. It corresponds to the transfer function of the RC filter implemented in the Maximum Voltage Retroaction electronics. So a correction could be applied to the amplitude of the gravimeter signals, for compensating the frequency dependant attenuation. This is a key point for achieving a precise calibration with the inertial platform method. We shall also correct the scale factor of the micrometric screw of the PET 1006 gravimeter. With this new results, it becomes possible by recording simultaneously the tidal signal with different gravimeters, to derive tidal factors for the Brussels station and thus to determine the scale factor of the T03 cryogenic gravimeter.
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José Arnoso, Ricardo Vieiral, Emilio J Velezl, Michel van Ruymb ...
2001 年 47 巻 1 号 p.
70-75
発行日: 2001/03/25
公開日: 2010/09/07
ジャーナル
フリー
Data from continuous observations with three Lacoste & Romberg gravity meters at station Cueva de los Verdes (Lanzarote, Canary Islands) are analysed. The tidal analysis shows, in general, a good agreement between the three meters. Correction from load and attraction effects permits to obtain better results when regional and local ocean models are considered, together with global ocean charts. The air pressure effect on two gravimeters exhibit important instrumental discrepancies.
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Trevor F Baker, Machiel S Bos
2001 年 47 巻 1 号 p.
76-81
発行日: 2001/03/25
公開日: 2010/09/07
ジャーナル
フリー
A set of well calibrated spring tidal gravimeter measurements in Central Europe and worldwide superconducting gravimeter observations from the Global Geodynamics Project (GGP) are compared with O1 and M2 model computations using the Dehant, Defraigne and Wahr (1999) body tide model and the latest global ocean tide models. For 01, the GGP measurements from different stations show a larger spread in the observed - model results for the in-phase component than for the out of phase (quadrature) component. This is attributed to calibration errors of up to ±0.3% at some of the GGP stations. This precludes further interpretation of the results in terms of lateral heterogeneities or inelastic body tide models. The phase lags of the gravimeters now appear to be well determined, which means that the out of phase components can provide useful tests of the ocean tide models.
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Gerhard Jentzsch, Peter Malischewsky, Maria Zadro, Carla Braitenberg, ...
2001 年 47 巻 1 号 p.
82-87
発行日: 2001/03/25
公開日: 2010/09/07
ジャーナル
フリー
The objectives of this common research project are to evaluate deformation field variations observed with different means in different geodynamical areas of high and low seismic hazards. By the combined analysis of different inputs and a complex interpretation of the changes of stress and deformation fields we hope to provide an improvement in seismic hazard assessment. Experimental requirements and possibilities were tested by model computations regarding areas of special interest. Besides the evaluation of different archives to select long-term deformation data the improvement of on-going experiments was one task of the work. To compare seismicity with deformation changes the separation of environmental signals is necessary (correction mainly of meteorologically and hydrologically induced effects on tilt and strain). Finite-element-modelling (FEM) is used to simulate the situations in the areas under study with regard to stress release and deformation. Under this co-operation the data in the archives of the partners from the NIS-countries (New Independent States) were made available, and a data base is being built up. Parts of these data are used here, and much more data still need to be treated. First results are presented.
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Giancarlo Dal Moro, Claudio Ebblin, Maria Zadro
2001 年 47 巻 1 号 p.
88-94
発行日: 2001/03/25
公開日: 2010/09/07
ジャーナル
フリー
Topography and cavities determine inhomogeneities of the uppermost crust deformational field. The present 3D Finite Element model of the Villanova tilt/strain station in the Friuli (NE Italy) seismic zone has been used for the interpretation of the observations in an area where several meteorological and hydrological effects interfere with the tectonic stress field, main target of the tilt-strain observations themselves. Special attention was devoted to the boundary stress (or strain) conditions acting at the border of the model. In many cases, as the Villanova one, the tectonic stress field orientation is not well defined. In that seismic area indeed two main tectonic structures (Alpine and Dinaric) collide and overlap each other. The dependence of the output from the position of the instruments inside the cave was also examined. The results are compared with the observed values of the air pressure variation. The results show that cavity and topography produce a consistent rotation as well as strain concentrations up to three times larger than those of the corresponding homogeneous isotropic medium.
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Carla Braitenberg, Maria Zadro
2001 年 47 巻 1 号 p.
95-100
発行日: 2001/03/25
公開日: 2010/09/07
ジャーナル
フリー
The techniques of autoregressive time series modeling by recursive filters are used to study and model the hydrologic induced signal in geodetic measurements. In particular, the recordings of tilt and extensometers installed in the seismically active Friuli area of NE-Italy are used in this study. The hydrologic influence is described from a statistical point of view, rather than from the physical processes that are involved. The time stability of the induction process is also studied. The method allows to discriminate hydrologic induced deformation signals from those due to pre/postseismic tectonic deformation.
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Gyula Mentes
2001 年 47 巻 1 号 p.
101-106
発行日: 2001/03/25
公開日: 2010/09/07
ジャーナル
フリー
Results of tidal and deformation measurements obtained by these two quartz tube extensometers are described. The deformations obtained by extensometers are com pared to the results of other geophysical measurements. Investigation of the Earth crust deformation is of great interest for studying recent geodynamical processes. For this reason a quartz tube extensometer with electrical recording was installed at the Geodynamical Observatory of the Geodetic and Geo physical Research Institute of the Hungarian Academy of Sciences in Sopron in 1990 and in 1993 a similar type of instrument developed at the same institute was placed in the uranium mine in Pecs. This later instrument was installed in order to study the local, spontaneous deformations and movements with the aim of tackling environmen tal and mining safety problems, next to accomplishing geodynamical measurements. This instrument was operative untill the mine was closed in 1999. Results of tidal and deformation measurements obtained by these two quartz tube extensometers are described. The deformations obtained by extensometers are com pared to the results of other geophysical measurements.
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Paul A Rydelek, Takao Eguchi, Isao Watabe, Sin-Iti Iwasaki, Yukio Fuji ...
2001 年 47 巻 1 号 p.
107-113
発行日: 2001/03/25
公開日: 2010/09/07
ジャーナル
フリー
At the sea-bottom of the Sagami trough subduction zone, south of the metropolitan area, central Japan, both temperature and pressure are continuously monitored with on-line tsunami sensors. These sensors are capable of measuring the changes in the corresponding thickness of the sea water layer to an accuracy of order mm, which suggests that the semidiurnal and diurnal oceanic tides are recorded with high resolution. We determined the amplitudes and phases of the major components of the periodic oceanic tides from a least squares analysis of a 1.5-year record of pressure data that partly included a temperature dependence. These results were then compared against those predicted from an oceanic model based on TOPEX/Poseidon data. Whereas we find good overall agreement between the observations and predictions, we also find some systematic differences. On average, the amplitudes of the tides in the oceanic model are found to mainly exceed the observed tides by several percent. Phase differences between observations and predictions are very small in the semidiurnal band but show departures in the diurnal band where observations lead predictions. Uncertainties in the oceanic models and unmodeled temperature effects may be able to explain these differences.
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Bernard Ducarme, Michel van Ruymbeke, Abdelbar El Wahabi
2001 年 47 巻 1 号 p.
114-120
発行日: 2001/03/25
公開日: 2010/09/07
ジャーナル
フリー
Two sites Menesplet (45° 01′ N, 06′E) near Bordeaux and Mordelles (48° 05′ N, 01° 51′ W) near Rennes in France have been occupied in 1997-98 with the LaCoste & Romberg gravimeter G906. The main goal is the study of the tidal loading along the Atlantic coast of France (Francis and Melchior, 1996). We compare the observed residual vectors with the load vectors derived from different oceanic tidal models. In Mordelles which is close to the complex zone between France, Great-Britain and Ireland we observe an improvement using CSR3.0 models compared to the old Schwiderski maps.
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Giovanna Berrino, Umberto Riccardi
2001 年 47 巻 1 号 p.
121-127
発行日: 2001/03/25
公開日: 2011/07/05
ジャーナル
フリー
Mt. Vesuvius is an active volcano located at the eastern boundary of Naples, Italy, in a densely populated area. Since the last eruption in March 1944, it is quiescent. Several geophysical studies are monitoring its activity. The volcano shows a generally low level seismicity, small ground deformation, gravity changes and a moderate gas emission. Since 1987 a recording gravity station operates on the volcano aimed at featuring the Earth tide transfer function in the area and continuous record of "nontidal" gravity changes. Here we focus on the results obtained from gravity records starting from 1994, after a break of about three years. Accurate calibration procedures ensure a frequent check of the instrumentation. A first order correction for the ocean loading and atmospheric effects are applied on the gravity data. Well-constrained tidal parameters have been so determined for the main tidal waves. The results have been compared with those obtained from gravity records spanning 1959-61, 1961-65 and 1987-91 years. The temporal trend of the tidal parameters and gravity residuals have been then compared with some features of the volcanic dynamics, mainly the temporal gravity changes detected by absolute and relative measurements and the time evolution of the seismicity. A large decrease of tidal parameters was observed from 1959-61 to 1961-65, while two significant increases occur from 1991 to 1994 and from 1998 to 1999. The latter "anomalies" appear to be time-correlated with some gravity changes resulting from absolute and relative measurements, and with seismic crises which occurred in the area. The observed phenomena may be indicative of a larger deformation behaviour of the volcanic area probably due to the change of the mean mechanical properties of the volcano.
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Sumio Yoshikawa, Takeyasu Yamamoto, Osamu Kamigaichi, Hirohito Naito
2001 年 47 巻 1 号 p.
128-133
発行日: 2001/03/25
公開日: 2010/09/07
ジャーナル
フリー
The strain records of the Double Coaxial Borehole Strainmeters (DCBS) installed at Odawara, Japan, were analyzed by focusing on the difference in the behaviors of the upper and lower sensors. In Stage 1(1989-1995), the behavior was characterized by strain steps and irregular changes with small correlation between the two sensors. In Stage II (1996- 1998), the long-term trends showed quite different behaviors with each other. Since steady contraction seen in the lower sensor resembled to the record of adjacent Borehole Strainmeter station at Yugawara, the lower sensor seemed to be stabilized in this period. In Stage III (1999-), behaviors of the two sensors became almost similar. Clear temporal changes corresponding to each stage could not be found both in the responses to the earth-and oceanic tide and the atmospheric pressure. FEM analysis suggested that the responses are strongly affected by the mechanical properties of the surrounding rocks. The recent trends in DCBS may reflect the regional stress state around the Odawara station.
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Yasuhiro Asai, Harumi Aoki, Torao Tanaka, Yuuichi Kitagawa, Shun-ichi ...
2001 年 47 巻 1 号 p.
134-140
発行日: 2001/03/25
公開日: 2010/09/07
ジャーナル
フリー
In order to investigate the distortion of crustal movement observation in borehole, we carried out the tidal analysis of strain, tilt and groundwater level observed at clustered borehole sites and compared the results. We obtained the following preliminary results: (1) The comparison indicates that observed strains of the boreholes are 2.3 times larger than theoretically predicted strains at the maximum. (2) M2 phase of Areal strain change is approximately 2.5 degrees in advance of those of groundwater level change, but O1 phase of Areal strain is approximately 3.0 degrees behind those of groundwater level change in TGR, and M2 and O1 phases of Areal strain change are approximately 28.1 and 2.3 degrees in advance of those of groundwater in 97FT-01. It is impossible to explain these phase shift using general models. (3) Groundwater level change in TGR and DH-2 agrees with each other within 1 cm and l degree, respectively. Though we have no hydraulic information for TGR, we have that of DH-2. From the information, we concluded that the plane confined aquifers in the both sites will be in the same physical condition, namely, the same structure as DH-2 will affect the strain observations in TGR. A similar situation is also expected for 97FT-01.
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Kensuke Onoue, Atsushi Mukai, Shuzo Takemoto
2001 年 47 巻 1 号 p.
141-147
発行日: 2001/03/25
公開日: 2010/09/07
ジャーナル
フリー
We have carried on observations of ground-strains and -tilts at Donzurubo Observatory, Nara, J apan since 1968. In order to investigate the local effect on tidal strain observations, we analyzed strain data obtained from three extensometers in Donzurubo during one year in 1999 by employing the Bayesian Tidal Analysis Program ‘BAYTAP-G’ and compared observational results with theoretical tidal strains calculated by ‘GOTIC2’ Program . As a result, observed tidal strains of the SE-2 component (N4.5° E) are well consistent with theoretical tidal strains . However, tidal strains observed with the SE-1 component (E4 .5° S) show extremely small amplitudes compared with theoretically expected ones, i.e. about one fourth of theoretically expected ones. Tidal strain amplitudes observed with the SE-3 component (N40.5° W) are 50-60 % of theoretically expected ones and maximum phase lag with this component is about 30 degrees for O1 constituent. We consider that the apparent amplitude reduction of tidal strains of SE-1 is mainly caused by the effects of anisotropy of the geological structure and the configuration of the mountain with a ridge and some part may be reflecting the topographic effect.
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Hans-Jürgen Dittfeld
2001 年 47 巻 1 号 p.
148-154
発行日: 2001/03/25
公開日: 2010/09/07
ジャーナル
フリー
On the 10
th Earth Tide Symposium in Madrid 1985 an investigation was referred concerning - among other tasks - tidal gravity results of two similar stations in Berlin and in Potsdam/Germany. There have been compared the results of contemporary time series of two different tidal gravimeters (LaCoste&Romberg ET18 and ASKANIA GS15 No. 222). Deviations of the amplitude factors at both stations were observed with a mean value in the order of 0.7 percent. Nowadays it became possible to perform such measurements with a more up-to-date equipment and to evaluate it with improved methods. So was installed a LaCoste&Romberg (Type G) gravimeter between 1997 and 1999 in turns at both the stations and the time series were analysed using the ETERNA 3.3 analysis program. Deviations of the tidal amplitudes are nearly of the same amount as in the 197811980 measurements but with an opposite sign. Therefore possible reasons are discussed with regard to the quality of the error estimations. Furthermore a lower noise level was observed in both periods at Insulaner station in the inner city of Berlin.
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Hiroshi Ishii, Gerhard Jentzsch, Steffen Graupner, Shigeru Nakao, Mark ...
2001 年 47 巻 1 号 p.
155-160
発行日: 2001/03/25
公開日: 2010/09/07
ジャーナル
フリー
Crustal deformation monitoring combined with seismic observations can be used in areas of high earthquake hazard in a joint interpretation for progress in earthquake research. Therefore, the 'Earthquake Research Institute' of Tokyo University runs the Nokogiriyama Observatory at the bay of Tokyo complementary to the seismological array. In April 1997 an Askania tiltmeter was deployed in a 10 m deep borehole in the observation gallery supplementary to the already installed water tube tiltmeters. It operated with only a small drift until June 1999. Recordings of the Askania and the water tube tiltmeters are compared with each other regarding signal/noise ratios, tidal residuals, ocean loading and meteorological effects to evaluate advantages and limitations of both instruments concerning future use in earthquake areas. First results of this comparison indicate generally good correspondence between the signals of the two instruments. Similarities and differences in the longterm drift, the tidal parameters and hydrologically and air pressure induced signals are discussed.
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Rüdiger Haas
2001 年 47 巻 1 号 p.
161-168
発行日: 2001/03/25
公開日: 2010/09/07
ジャーナル
フリー
This paper gives a very short overview on some important publications dealing with the determination of tidal effects by space geodetic techniques.
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Lorenzo Iorio, Erricos C. Pavlis
2001 年 47 巻 1 号 p.
169-173
発行日: 2001/03/25
公開日: 2011/07/05
ジャーナル
フリー
The tiny general relativistic Lense-Thirring effect can be measured by means of a suitable combination of the orbital residuals of the nodes of LAGEOS and LAGEOS II and the perigee of LAGEOS II. This observable is affected, among other factors, by the Earth' s solid and ocean tides. They induce long-period orbital perturbations that, over observational periods of few years, may alias the detection of the gravitomagnetic secular trend of interest. In this paper we calculate explicitly the most relevant tidal perturbations acting upon LAGEOSs and assess their influence on the detection of the Lense-Thirring effect. The present day level of knowledge of the solid and ocean tides allow us to conclude that their influence on it ranges from almost 4% over 4 years to less than 2% over 7 years.
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Bin Wu, Peng Bibo, Yaozhong Zhu, Houze Hsu
2001 年 47 巻 1 号 p.
174-180
発行日: 2001/03/25
公開日: 2010/09/07
ジャーナル
フリー
Precise satellite laser ranging (SLR) measurements with normal point precision of a few millimeters observed by globally distributed stations made it possible to estimat tidal signals from satellite orbit perturbations and site displacements. In this paper, we discuss how to use SLR or satellite tracking to estimate Love numbers at 18.6 year, M
M, M
1, K
2, O
1, M
2 and S
2 tidal waves. The results compared with the other space geodetic results and theoretical models with good agreement indicate that SLR is an effective technique suited to provide observation constraints for the Earth tide studies.
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Shigeru Aoka, Taku Ozawa, Kazuo Shibuya, Akihiro Masuyama
2001 年 47 巻 1 号 p.
181-186
発行日: 2001/03/25
公開日: 2010/09/07
ジャーナル
フリー
Displacement of the fast sea ice was observed with differential kinematic GPS technique at Nisi-no-ura Cove in Lutzow-Holm Bay, Antarctica. The observations were carried out for eight months from April to December in 1998. The results were evaluated with bottom pressure gauge (BPG) measurements. Tidal displacements were obtained clearly for both measurements. From the difference between both measurements, the GPS vertical accuracy was estimated to be 1-1.5 cm. Tidal constituents derived from the GPS observations were consistent with those from the BPG observations; the “sensitivity ratios”, conversion coefficient from BPG output to sea level, derived for six major tidal components were around 0.98 and the phase lags for the major com ponents agreed within 1°. Horizontal motions on the tidal time scales were detected, but the motion is less than a few centi-meters and much less than that on the longer time scale. Thus, GPS has demonstrated the ability to monitor tides with sufficient accuracy.
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Yuki Hatanaka, Arata Sengoku, Tadahiro Sato, James M. Johnson, Christi ...
2001 年 47 巻 1 号 p.
187-192
発行日: 2001/03/25
公開日: 2010/09/07
ジャーナル
フリー
The tidal displacement signals are derived for the Japan area from the GPS Earth Observation Network (GEONET) of Geographical Survey Institute. The amplitude of these tidal signals is up to 2.5 cm and most of them are explained by the ocean tide loading displacement model by Matsumoto et al. (2000, 2001). The loading tide signals affect the troposphere delay estimates by more than 1 cm in southwestern Japan if they are not corrected. These tidal signals in the displacement and troposphere estimates are effectively eliminated by applying the ocean tide loading correction with the model for most of the major tidal constituents. The comparison of residual tidal signals by applying the two ocean loading models shows reduction of the residual M2 tidal signals by applying the correction with the newer model. These results demonstrate the capability of a dense GPS network to detect un-modeled tidal signals.
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Péter Varga, Jâzsef Zàvoti, Erwin Groten, Kuros Ar ...
2001 年 47 巻 1 号 p.
193-197
発行日: 2001/03/25
公開日: 2011/07/05
ジャーナル
フリー
More than two years of continuous GPS observations in 1995-1997 completed by the International GPS service are analysed in terms of polar motion (PM) and length of day (LOD) in view of daily/subdaily variations. The aim of the research carried out was a complex study of these two phenomena which allows us to conclude that • the most prominent components of the record in the daily/subdaily frequency band were found at the tidal frequencies. The long periodic zonal tides were not detected in case of PM. The tesseral (diurnal) frequency anomalies are of Earth tidal origin (their amplitudes are around 1 mas). The semi-diurnal sectorial waves are around 0.1-1 mas and they are generated by oceanic tides. In case of LOD the most significant spectral amplitudes were found in case of zonal fortnightly M
f wave and in the semi-diurnal band for M
2 wave. The order of the observed amplitudes is 10
-3 s, •regular high frequency anomalies were observed in the frequency band 3-11 cy cles/day. These effects can influence amplitude values at diurnal and semi-diurnal frequency bands, too. These anomalies are caused by the atmospheric tides, •the LOD time series of 1995-1997 was carefully compared with the seismological data catalogue of the US Geological Survey and there was no short periodic daily/subdaily signal found which could be connected to earthquake activity.
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Toshimichi Shirai, Toshio Fukushima
2001 年 47 巻 1 号 p.
198-203
発行日: 2001/03/25
公開日: 2010/09/07
ジャーナル
フリー
We detected the Free Core Nutation (FCN) directly and revealed the time variation of FCN from the analysis of the Very Long Baseline Interferometry (VLBI) observation for the period 1979.9-2000.1. We developed the model of the FCN which consider both the energy dissipation due to the viscosity of fluid core and the magnetic coupling of core-mantle boundary and the excitations during the observation period. From the analysis of VLBI data, we discovered that the FCN is of the damped oscillation which had 4 significant excitations at 1989.90 ± 0.40, 1994.47±0.40, 1994.76±0.40, and 1998.99±0.40. And then these epochs roughly coincide with the occurrence of some huge earthquakes, namely whose amplitude are bigger than Mw 8.0.
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Hans-Georg Scherneck
2001 年 47 巻 1 号 p.
204-212
発行日: 2001/03/25
公開日: 2011/07/05
ジャーナル
フリー
Thanks to a parametrised solid earth tide model that efficiently (with a minimum set of parameters) describes the transfer response of the earth to the input tide potential in harmonic decomposition it is possible to obtain high-sensitivity in determination of the frequency and quality factor of the liquid core nearly-diurnal free nutation from observation of ground water tides in deep wells. The response is enhanced because of the fortunate Love number combination that applies to volumetric strain and the way the resonance affects the
h and ι Love numbers. In crystalline rocks shear strain coupling can enhance or attenuate this relation further. A limiting factor is the presence of ocean loading tides. Even in cases far away from coasts the effect is significant; however, there it can be modelled with sufficient accuracy. An example is shown from ground water pressure measurements in a 700 m deep borehole in south-east Sweden. Six months of data provide enough sensitivity to estimate the resonance frequency to be bracketed between 380 and 440 days.
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Toshio Fukushima
2001 年 47 巻 1 号 p.
213-218
発行日: 2001/03/25
公開日: 2010/09/07
ジャーナル
フリー
Derived were the mathematical expressions of several longitude origins on a moving equator. Their motions in space were illustrated for a simple model of the motion of a pole. Noted was the global secular rotation of Guinot's non-rotating origin (NRO) (Guinot 1979) with respect to the inertial reference frame. Such secular rotation does not appear in the motions of some origins defined geometrically. Among them, recom-mended was the foot of the x-axis on the moving equator. This is partly because it is independent on the adopted value of obliquity at the epoch in the case of precessional motion of the Earth's pole. And this is partly because it is directly accessible through the angular observations referred to the moving equator such as the time measurement of prime meridian passage of quasars by VLBI facilities on the Earth.
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Piravonu M Mathews
2001 年 47 巻 1 号 p.
219-224
発行日: 2001/03/25
公開日: 2011/07/05
ジャーナル
フリー
This paper presents an outline of an integrated treatment of solid Earth deformations, ocean tides, wobbles of the mantle and the core regions, and the nutations associated with the mantle wobble, all resulting from the action of the tesseral tide generating potential (TGP) with its spectrum of nearly diurnal frequencies. The interplay of these phenomena makes such a treatment necessary for accurate computation of any of these responses to forcing in the diurnal tidal band, including that of the Love and Shida number parameters and the gravimetric factor parameters, which characterize the Earth's deformational response.
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Shuhei Okubo, Daijiro Tsuji
2001 年 47 巻 1 号 p.
225-230
発行日: 2001/03/25
公開日: 2010/09/07
ジャーナル
フリー
Traditional Green's functions have been used for estimating the effect of oceanic loading upon modern geodetic observations, such as superconducting gravimetry, GPS, VLBI and SLR. To improve the estimation accuracy, we introduce the effects of the earth's anelasticity while considering its frequency dependence (Absorption Band Model). It turns out that phase lags of Green's functions are of order 2 degree or less but they are strongly dependent on Q sturcture. Physical Dispersion disturbs the real parts of Green's function by 2 % or less.
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Piravonu M Mathews
2001 年 47 巻 1 号 p.
231-236
発行日: 2001/03/25
公開日: 2010/09/07
ジャーナル
フリー
The definitions of the various tidal parameters are recalled, and numerical values are presented for the constants in resonance formulae expressing their frequency de pendence in the diurnal band. Values of the Love/Shida number and gravimeric factor parameters are also tabulated for some of the major diurnal tides.
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Mark S Schenewerk, J Marshall, William Dillinger
2001 年 47 巻 1 号 p.
237-242
発行日: 2001/03/25
公開日: 2010/09/07
ジャーナル
フリー
The proliferation of permanent Global Positioning System (GPS) tracking sites and improvements in estimating the vertical component of a site's coordinates from GPS measurements present an opportunity to directly observe the crustal deformation caused by loading from ocean tides. The long, continuous record from these sites enables the accumulation of observations coherently with respect to the driving tidal forces, and estimates of the ocean-loading signal can be made from these accumulated observations. Techniques like this defeat atmospheric, geometrical, and multipath effects which can have a comparable magnitude, but do not have the same period as ocean-loading. A project to estimate ocean-loading effects at sites globally was undertaken at the Geodetic Research Division of the National Geodetic Survey. The technique used in and results of that project are presented here. Emphasis will be placed on the diurnal and semi-diurnal tidal signals. Although excellent agreement with existing models is found for most sites, a large fraction, generally those at higher latitudes where the complex coastlines and poorer ocean tidal data begin to dominate, show significant differences from standard ocean-loading models.
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Koji Matsumoto, Tadahiro Sato, Takashi Takanezawa, Masatsugu Ooe
2001 年 47 巻 1 号 p.
243-248
発行日: 2001/03/25
公開日: 2010/09/07
ジャーナル
フリー
Oceanic tidal loading signals are in general smaller than solid Earth tide signals, but they can be measured by geodetic technique and need to be accurately corrected for because they are in general a source of noise. In order to meet this requirement we have developed a program to compute the loading tide most accurately in Japanese region by using a combination of global and regional ocean tide models and fine-scale land-sea grids. The program computes six kinds of loading (radial and horizontal displacements, gravity, tilt, strain, and deflection of the vertical) for 21 constituents including long-period tide.
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Tonie M van Dam, John M Wahr, P. Chris D Milly, Olivier Francis
2001 年 47 巻 1 号 p.
249-254
発行日: 2001/03/25
公開日: 2010/09/07
ジャーナル
フリー
Five years of global continental water storage variations are used to predict the effects of long-wavelength, long-period variability in water storage on gravity obser vations. At the sites of existing superconducting gravimeters, the modeled gravity changes have root-mean-square (RMS) values of as much as 7 μGals, with ranges of up to 22 μGals. Variations much larger than these values can be found over large regions the globe. We find that the gravity effects are predominantly annual in char acter. We also find that the modeled responses to water loading exhibit long-period variations that could be mistaken for secular tectonic trends when observed over a time span of a few years.
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Duncan Carr Agnew
2001 年 47 巻 1 号 p.
255-260
発行日: 2001/03/25
公開日: 2010/09/07
ジャーナル
フリー
Time-varying surface loads affect many geodetic quantities. To help in understanding this process, I describe map projections which show an area of the Earth's surface in proportion to the influence a load at that location would have on a measurement at a given place. Such maps illustrate the great importance of nearby regions compared with those more distant, and should be helpful in evaluating possible errors in the computation of loading effects.
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Atsushi Mukai, Shuzo Takemoto, Toshihiro Higashi, Yoichi Fukuda
2001 年 47 巻 1 号 p.
261-266
発行日: 2001/03/25
公開日: 2010/09/07
ジャーナル
フリー
Routine observations of gravity changes have been performed at Kyoto, Japan and Bandung, Indonesia by employing superconducting gravimeters. Kyoto and Bandung are surrounded by the Pacific Ocean and other oceans. Gravity changes due to oceanic loading tides have a detectable signal level at each station. We can investigate viscosity of the crust and the upper mantle using differences between observed values and expected values of oceanic loading tides. Observed phase in the oceanic tidal loading has a deviation about 10 degrees from the predicted phase in major parts of tidal constituents, though phase lag due to viscosity in the Earth is expected to be 0.1 degree or less.
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Jean-Paul Boy, Pascal Gegout, Jacques Hinderer
2001 年 47 巻 1 号 p.
267-272
発行日: 2001/03/25
公開日: 2010/09/07
ジャーナル
フリー
We show the reduction (about 10-20 %) of surface gravity residues by correcting gravity data from superconducting gravimeters (SG) of the GGP (Global Geodynamics Project) network from global atmospheric loading. We use a Green's function formalism and global pressure charts provided by NCEP (National Center for Environmental Prediction) and compare the loading correction to an empirical local barometric admittance correction. We can also validate the inverted barometer (IB) hypothesis as the oceanic response to pressure loading for periods exceeding 5 days. Non-inverted barometer (NIB) hypothesis is shown to be an inadequate assumption for describing the ocean response to atmospheric pressure.
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Makio Ishiguro
2001 年 47 巻 1 号 p.
273-280
発行日: 2001/03/25
公開日: 2010/09/07
ジャーナル
フリー
In the field of Earth science, there is a problem of decomposition of tidal data. We published a Bayesian tidal analysis program, BAYTAP-G about 15 years ago. BAYTAP-G decomposes given series into four components, drift component air pressure effect component, tidal component and residual. There are at least two different purposes of the decomposition. For scientists who are interested in the global response of Earth to lunar-solar force, the necessary information is contained in the tidal component and the drift component is noise. On the other hand, for scientists who are interested in the local crustal movement, the information is contained in the drift component and the tidal component is noise. BAYTAP-G can be used by both types of scientist but uses one and the same Information Criterion, Akaike Bayesian Information Criterion ABIC, to evaluate the goodness of the decomposition, regardless of the difference in the purpose of the anal ysis. ABIC is a statistics used to evaluate the goodness of Bayesian model fitted to given data. The use of ABIC in this context is justified because the decomposition can be regarded as a Bayesian procedure in the framework of Bayesian statistics. The decomposition procedure employed in BAYTAP-G, however, has other inter pretations. The procedure can be regarded as a special case of penalized log likelihood maximization procedure. Under this interpretation, there is a possibility of criteria for the evaluation of the goodness of the decomposition which take the purpose of the analysis into the consideration. The present paper demonstrates the necessity and the possibility of such criteria based on a simulation study of the tidal analysis.
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Angel Venedikov, José Arnoso, Ricardo Vieira
2001 年 47 巻 1 号 p.
281-286
発行日: 2001/03/25
公開日: 2010/09/07
ジャーナル
フリー
A general description of the algorithm used by a new computer program for tidal data processing is presented. The main stages of the algorithm are: (i) filtration of intervals without overlapping and (ii) application of the Method of the Least Squares on the filtered numbers. A new element is that all series of filtered numbers, related with different tidal species are processed all together. It is shownthat this way of analysis may be equivalent to a direct processing of the data, without any filtration. However, the processing of the filtered numbers has the advantage to provide frequency dependent estimates of the precision. Another new element is that the program can be applied on totally unevenly spaced data.
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Hans-Jürgen Dittfeld
2001 年 47 巻 1 号 p.
287-293
発行日: 2001/03/25
公開日: 2010/09/07
ジャーナル
フリー
While the significance of air pressure coefficients in tidal analysis results is unquestionable, and their application clearly improves the results, the correlation with other environmental parameters is often weak and improvements are rather small if they are introduced. In spite of the progress in modelling in recent years, there seems to be a limit to the accuracy that can be achieved, and one has rather to look for possibilities of avoiding some environmental influences from the beginning. Some reasons for the disappointing success of this correlation are here discussed for a 6-year recording of a superconducting gravimeter operating in Potsdam. We are particularly concerned with groundwater level, room temperature, and rainfall. Even though the residual noise is more or less decreased, the results are practically independent of the influence of the additional parameters. It is shown that the correlation is not persistent enough through the data to achieve the expected improvement, or perhaps on the other hand the actual influences are partly screened. For example, the effect of rainfall is difficult to estimate if the water flows superficially away from the station and the soil moisture does not correspond to the precipitation at the point of the rain gauge.
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Wataru Morii
2001 年 47 巻 1 号 p.
294-299
発行日: 2001/03/25
公開日: 2010/09/07
ジャーナル
フリー
A new method of spectral analysis suitable to examine the Earth's background free oscillations was developed. The basic principle of this method is based on a technique of an AM receiver . A remarkable feature of this method is high resolving power for time variation of signal intensities . Using with this method, diurnal variations in the Earth's background free oscillations were clearly confirmed.
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Bruno Meurers
2001 年 47 巻 1 号 p.
300-307
発行日: 2001/03/25
公開日: 2010/09/07
ジャーナル
フリー
Superconducting gravimetry has been proven to be extremely helpful when seeking answers to open questions related to temporal gravity variations in a wide range of geophysical and geodynamic research. This is especially true if superconducting and absolute gravimetry is combined. Within the framework of GGP (Global Geodynamics Project) about twenty superconducting gravimeters with a comparable instrumental standard are in operation since 1997. Recent results of different research targets are discussed covering important questions like those for the inner structure of the earth, atmospheric and environmental effects, atmospheric loading, ocean models and earth rotation. Some of these problems are closely linked to each other, and a successful approach to the solution of a certain problem often implies addressing additional questions. This applies to both data processing and interpretation. Another key issue for obtaining highly reliable results is the accurate calibration and the stability of both the gravimeter and the air pressure sensor. Some questions regarding instrumentation and station noise are discussed.
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Bernard Ducarme, He-Ping Sun
2001 年 47 巻 1 号 p.
308-315
発行日: 2001/03/25
公開日: 2011/07/05
ジャーナル
フリー
The globally distributed gravity observations of the Global Geodynamics Project (GGP) network of superconducting gravimeters allow us to determine the characteristics of the small tidal waves, especially those with a frequency close to the core resonance. Before drawing any conclusion from the data it is compulsory to correct the oceanic tidal loading effects. As most of the cotidal maps exist only for the main waves, it was necessary to interpolate the dynamic response of the oceans for the additional groups, taking into account the effects of the core resonance on the oceanic response to the tidal force. We successfully used the Wahr and Sasao (1981) model of this resonance, and as a first test used the Schwiderski (1980) standard model for oceanic tides. The corrected amplitude factors and phase differences were compared with the Dehant, Defraigne and Wahr models for the response of the Earth to the tidal forces. We paid a special attention to the core resonance, trying to check if the phase lag of K
1 and ψ
1 is systematically positive while it is negative for φ
1, as suggested in the latest model of Mathews (this issue) which includes new features such as electromagnetic interactions at the core-mantle boundary.
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Jürgen Neumeyer, Eric Brinton, Piet Fourie, Hans-Jurgen Dittfeld, ...
2001 年 47 巻 1 号 p.
316-321
発行日: 2001/03/25
公開日: 2010/09/07
ジャーナル
フリー
In February 2000 the reconstructed Dual Sphere Superconducting Gravimeter (SG) with two gravity sensors has been installed at the newly constructed South African Geodynamic Observatory Sutherland (SAGOS). Additionally meteorological sensors and a ground water table sensor are installed for estimation of gravity changes induced by the atmosphere and hydrosphere. The quality of the site is discussed according to the requirements for a SG site. The difference of the tilt minima for both sensors is adjusted to about 4.5 nm/s
2. For both gravity sensors the calibration factors have been determined by comparison with a well calibrated LaCoste & Romberg Gravimeter which records to the SG in parallel. With a recently developed low frequency sine and square wave generator based on a PC a step response experiment has been carried out to determine the transfer function and to calculate the instrumental time lag. The station is remote controlled by a “Multi Media Monitoring Controlling and Information System” (M
3CIS) which operates in real time via Internet. The preliminary short period tidal parameters have been determined for both sensors which are in good agreement. An amplitude spectrum presents the gravity residuals. The single atmospheric pressure admittance is determined for both sensors.
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