SGD23-01

Room:102A

Time:May 27 16:15-16:30

The new insight for earthquakes, based on the satellite gravimetry.
TANAKA, Yusaku1∗ ; HEKI, Kosuke1 ; MATSUO, Koji2
1

Graduate School of Science, Hokkaido University, 2 Geospatial Information Authority of JapanThe GRACE satellites observe gravity changes by huge earthquakes. Since the GRACE satellites were launched in 2002,
several gravity changes have been reported such as the coseismic gravity changes by the 2004 Sumatra-Andaman earthquake, by
the 2010 Maule earthquake, and by the 2011 Tohoku-oki earthquake. For the 2004 Sumatra-Andaman earthquake, not only thecoseismic gravity change but also the postseismic gravity change has been reported.
I’ll explain about three topics:(1) Topic 1
The mechanisms of coseismic gravity changes by shallow-focus earthquakes have almost been revealed by previous studies.
First, I’ll introduce the knowledge about it.
(2) Topic 2
I researched the postseismic gravity changes with newer data than those used in previous studies and found the postseismic
gravity changes had two components. After decreasing coseismically, the gravity continued to decrease for a first few months
and turned to increasing. In my opinion, these two components can be related to afterslip and viscoelastic relaxation. These two
phenomena are hard to separate, so they often get into topics in scientific meetings. The result of my study suggests that it would
become possible by using the gravity data.
(3) Topic 3
The GRACE satellites also caught the coseismic gravity change of the 2013 Okhotsk deep earthquake (Mw8.3, depth at
604km) and I found it came from the ground deformation. The gravity field is changed coseismically by three main causes, i.e.,(1) ground uplift and subsidence, (2) Moho uplift and subsidence, and (3) density changes under the ground. The density changes
were dominant in the 2004 Sumatra-Andaman earthquake, the 2010 Maule earthquake, and the 2011 Tohoku-oki earthquake. But
in the 2013 Okhotsk deep earthquake, the dominant cause was not density changes but ground deformations. The density changes
occurred at a depth of about 600km. This was so deep that the GRACE could not catch it. But the ground uplift and subsidence
had so long distance from each other that the GRACE was able to catch the signals. This means that the GRACE is the first tool
for the two-dimentional signals of ground deformations by deep earthquakes.
Keywords: GRACE, Postseismic gravity changes, Coseismic gravity changes, Afterslip, Viscoelastic relaxation, Deep-focus
earthquakes

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SGD23-02

Room:102A

Time:May 27 16:30-16:45

Admittance between gravity and topography show the moon’s lithosphere
SAEGUSA, Yuki1∗ ; HEKI, Kosuke2
1

Department of Natural History Sciences, Graduate School of Science, Hokkaido University, 2 Department of Natural History
Sciences, Faculity of Science, Hokkaido University
The Moon is the only natural satellite of the Earth, and is believed to be formed by an impact of a Mars-sized body with theprimitive earth, and the subsequent integration and cooling of fragments formed in the impact. The Moon is an important key toinvestigate the early history of the solar system because it preserves the ancient surface and is the most accessible planetary bodyfrom the Earth. Investigating the formation and evolution of the Moon requires an understanding of the interior structure, heatgeneration, and differentiation.
The lunar exploration has started with the invention of the optical telescope by Galileo Galilei, which enabled us to see thetopographic irregularity of the lunar surface. In the 20th century, scientists sent various probes to the Moon, and have been trying
to explore its interiors by various observations with lunar landers and from lunar orbiters.
In this study, we study the relationship between the free-air gravity model from the GRAIL (Gravity Recovery and Interior
Laboratory) mission and topographic model from the laser altimetry in the LRO (Lunar Reconnaissance Orbiter) mission. In
the GRAIL mission gravity field was derived from the changes in the distance between the two identical satellites on the same
orbit. The gravity and topography showed low/high correlation in the low/high degree components. This means that isostaticcompensation is highly achieved for long wavelength features due to the ductile flow in the lunar mantle, and that the short wavelength topography is mainly supported by lithospheric strength. For the topography of very short wavelength, with degree/orderexceeding 400, the correlation again becomes low due to errors in the gravity model.
It is important to compare the correlation between the gravity and topography of not only the Moon but also other terrestrial
planets, such as Mars and Venus, to study degree of isostatic compensation and lithospheric thickness. For example, Mars islarger than the Moon and smaller than the Earth, and its lithospheric thickness and the degree of isostatic compensation will also
be between the Moon and the Earth.
In addition to the correlation, we study the admittance, which is defined as the amplitude ratio of topography and gravity
anomalies. The admittance is important in the discussion of the thickness of the lithosphere that can support the surface irregularity as an elastic body (referred to as elastic thickness here). Generally, a larger planet has larger surface heat flow andthinner lithosphere. Thin lithosphere would cause high degree of isostasy for the topography of the shorter wavelength. For theMoon, small admittance for long wavelength topographies quickly becomes larger, and the admittance keeps constant at about
110 mgal/km for degrees larger than 50.
Based on the theory in Watts (2001), we estimated the elastic thickness of the Moon as ˜14 km. This thickness is comparable
to those found in the present Earth in spite of the smaller dimension of the Moon. This may suggest that the majority of the
topographic features on the Moon was formed in the early stage of the Moon, when the moon was not so cold as it is today.
In planetary physics, it is important to compare different planets and moons from various aspects. The present study suggeststhat the Moon still conserves the state of the early-stage isostasy as a fossil to investigate its ancient elastic thickness. After all,it is important to consider not only size but also age of the topography in discussing the elastic thickness of a planet or a moon.

Keywords: the moon, topography, gravity anomaly, lithosphere, correlation, admittance

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SGD23-03

Room:102A

Time:May 27 16:45-17:00

Systematic error evaluation of the compact absolute gravimeter TAG-1
ARAYA, Akito1∗ ; SAKAI, Hirotaka1 ; TAMURA, Yoshiaki2 ; TSUBOKAWA, Tsuneya3 ; SVITLOV, Sergiy4
1

ERI, Univ. Tokyo, 2 NAOJ, Mizusawa, 3 Shin-ei Keisoku, 4 Inst. Geodesy, Univ. Hanover

In recent years, absolute gravimeters are used not only for determining static or secular-changing gravity field but for observing
dynamic gravity change associated with movement of underground fluid, such as groundwater and magma. For the latter purpose,
we have developed a compact absolute gravimeter, TAG-1, to use it for continuous monitoring volcanic activities at a site close
to the volcanic vent. As compared to relative gravimeters, absolute gravimeters enable continuous stand-alone measurements
without any round-trip comparison to the gravity reference point.
In July of 2013, we carried out a short-term observation at Kirishima volcano observatory (Miyazaki, Japan) using TAG-1 [1].
The statistical error was 0.8 uGal for one-day observation. Measured absolute gravity, however, showed reduction of 20-25 uGalfrom preceding observation in March of 2012. The regional crustal deformation inferred from GPS data suggested the reduction
probably originated from instrumental error of TAG-1. We consider two error sources: recoil vibration and photo-detector
response. The recoil force is generated at the time of releasing a free-fall mass and actuates the floor, resulting in vibration of thereference mirror. Slight phase delay determined by the photo detector causes systematic error in the gravity calculated from thequadrature fringe data [2].
In this presentation, both errors are evaluated, and performance of TAG-1 including its accuracy after the error correction is
discussed.
References[1] A. Araya, H. Sakai, Y. Tamura, T. Tsubokawa, and S. Svitlov, ”Development of a compact absolute gravimeter with abuilt-in accelerometer and a silent drop mechanism”, in Proc. of the International Association of Geodesy (IAG) Symposiumon Terrestrial Gravimetry: Static and Mobile Measurements (TGSMM-2013), 17-20 September 2013, Saint Petersburg, Russia,
98-104 (2014).
[2] S. Svitlov and A. Araya, ”Homodyne interferometry with quadrature fringe detection for absolute gravimeter,” Appl. Opt.
53, 3548-3555 (2014) .

Keywords: absolute gravimeter, systematic error, volcano, Kirishima, recoil, photo detector

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SGD23-04

Room:102A

Time:May 27 17:00-17:15

Performance evaluation of a test mass launch system including a reaction reduction mechanism for a rise-and-fall AG
SAKAI, Hirotaka1∗ ; ARAYA, Akito1 ; TSUBOKAWA, Tsuneya2
1

Earthquake Research Institute, University of Tokyo, 2 Shin-ei Keisoku

We describe the test mass launch system including a reaction reduction mechanism for the compact rise-and-fall absolutegravimeter (AG). Absolute gravimeters measure the local value of the gravitational acceleration g in the accuracy of few µgal
(1µgal = 10−8 ms−2 ). Absolute gravimeters are used to establish the gravity standard network. They can be also used to surveyof magma movement in the volcano. The data provide significant information of volcanic activities and various studies are proceeded to estimate volcanic eruptions and underground density structures. Absolute gravimeters are accurate, but the equipment
is too bulky and heavy for field observation. As a result, for volcanic observations, a gravity value is usually measured by anabsolute gravimeter at a reference point of foot, and then a gravity value of an observation point can be obtained from the gravity
difference of a reference point and an observation point measured with the relative gravimeter. Therefore such an observationis troublesome, and requires long time. An apparent gravity change by the drift of the relative gravimeter happens, and measurement accuracy may worsen. Furthermore it is dangerous to observe at a reference point when a volcano erupts. If compact
absolute gravimeters are completed and put to a volcanic area, we will acquire accurate data continuously even when the volcano
is active. To achieve these, my studies are very important.
We adopt a rise-and-fall method to realize the downsizing of the absolute gravimeters. The measurement of gravity acceleration is based on the reconstruction of the orbit of the test mass thrown up or dropped in vacuum chamber. This method hassome advantages. The simple free-fall method has several problems such as bulky mechanism to lift up the test mass, repeatedmeasurements, and long time to take for the preparation. Hence, we developed the launch equipment that has no need for lifting
up the test mass and can measure repeatedly. In addition the finite speed of light effect and drag effect are offset. As a result,
systematic error becomes small. The equipment can throw up the test mass by 3mm in height simply by applying the signal toa piezoelectric element which is incorporated in the displacement enlarging mechanism. And the reaction reduction system is
attached for the purpose of improvement of the measurement accuracy. When the test mass is thrown up, the floor recoil affects
the interferometer and generates a systematic error. Specifically, we put the same piezoelectric element and the displacement
enlarging mechanism on the other side of the baseplate to which the launch system is attached. These displacement enlarging
mechanisms move symmetrically by applying the same signal to the piezos. When the test mass is thrown up, the counter mass
fixed by springs is launched downwards at the same time to compensate the recoil effect. Moreover, to avoid the vibration
occurrence by movement of displacement enlarging mechanism, we applied the signal of which acceleration is as continuous
as possible. We could observe the reaction as much as 20% of peak acceleration without its mechanism. The result of gravity
measurement in February and development status will be reported.
Keywords: absolute gravimeter, launch system, reaction reduction mechanism, gravity, prediction of volcanic eruption, estimating a subsurface density structure

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SGD23-05

Room:102A

Time:May 27 17:15-17:30

Development of a portable laser-interferometric gravity-gradiometer
SHIOMI, Sachie1∗
1

Sachie Shiomi

We are developing a portable laser-interferometric gravity-gradiometer for environmental measurements. In the gravity gradiometer, differential accelerations between two test masses, which are in free fall at different heights in a vacuum tank, aremeasured by a laser interferometer. A prototype of the gravity gradiometer was built up, and its performance was tested at the
Sakurajima Volcanological Laboratory of the Kyoto University. We will report the current status of the development.
Keywords: gravity gradients, environment measurements

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SGD23-06

Room:102A

Time:May 27 17:30-17:45

Making of Japanese domestic gravity data which consistent to Japan gravity standardization net 2013
MIYAZAKI, Takayuki1∗ ; YOSHIDA, Kenji1 ; MIYAHARA, Basara1
1

GSI of Japan

Geospatial Information Authority of Japan (GSI) have established a new gravity standardization net of Japan, the Japan Gravity
Standardization Net 2013 (JGSN2013), from the latest absolute and relative land gravity data which covers all Japanese islands.
JGSN2013 have achieved great improvement in accuracy and special coverage by adopting FG5 absolute gravity meter as an instrument, updating station coordinates to ITRF2008 and modifying tidal correction procedure to more consistent manner throughall process.
Furthermore, GSI conducted second order gravity survey which covers 14,000 stations all over Japan from 1967 to 1993. The
latest gravity data archive of Japan which have higher spatial coverage and consistency with FG5 will be established from thearchived data of 14,000 stations by converting them to those which are consistent with JGSN2013.
However, error checking and least square data processing of huge second order gravity data which are same procedures as
those of fundamental and first order gravity data will take huge time and efforts. Moreover, second order gravity data has lower
precision than first order gravity data because GSI adopted different gravimeter and procedure and the results contain several
additional errors including observation errors. In addition, even if we adopt the same data processing as first order gravity data
for second order gravity data analysis, we could not get the equivalent precision for second order gravity values to first order
gravity values. Therefore, we are trying more efficient methods of converting original second order gravity data to new gravity
data set which are consistent with JGSN2013, by developing conversion parameters from JGSN75 to JGSN2013. Our purpose
is to develop an interpolation method which gives the most consistent parameters for conversion from original gravity data to
JGSN2013 without generating artifacts. The model should express the relationship between two datasets and be consistent withthe actual differences.
The development of the method for conversion from original second order gravity data to JGSN2013 is reported in this paper.

Keywords: JGSN2013, second order gravity survey

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SGD23-07

Room:102A

Time:May 28 09:00-09:15

Gravity anomalies and ice mass movements around the Japanese Antarctic stations in East
Antarctica
FUKUDA, Yoichi1∗ ; AOYAMA, Yuichi2 ; DOI, Koichiro2 ; YAMAMOTO, Keiko3 ; MATSUO, Koji4 ;NOGI, Yoshifumi2
1

Graduate School of Science, Kyoto University, 2 National Institute of Polar Research, 3 Institute of Space and Astronautical
Science, Japan Aerospace Exploration Agency, 4 Geospatial Information Authority of JapanThe region from Dronning Maud Land to Enderby Land in East Antarctica, where a Japanese Antarctic station Syowa islocated, is a key area for investigating the formation of Gondwana, because reconstruction models suggest a junction of thecontinents locates in the area. There is Shirase Glacier, one of the major glaciers in Antarctica, which controls the ice sheet floorof the area. Moreover, recent investigations using GRACE, IceSat/Envisat, and other geodetic and/or glociological measurements
show the mass increase in the area. Therefore the area is also important for glaciological and GIA studies.
To contribute to these investigations as well as enhancing gravimetric networks, the Japanese Antarctic Research Expedition(JARE) has been conducting gravity measurements in the area for a long time. Combining these in-situ gravity data and GOCE
EGMs recently released, gravity fields in the area have been newly determined by means of Least Squares Collocation. In
addition, JARE-55 (the 55th JARE) conducted the absolute gravity measurements at a gravity base point on the Seal rock near
the Asuka station in the Sor-Rondane Mountains. There results have been reported in the previous JpGU meetings and otheropportunities.
In the area, JARE-28 conducted gravity measurements along a N-S traverse line from Breid bay to Sor-Rondane Mountains
via Asuka station. The absolute gravity value obtained by JARE-55 was employed to reevaluate the gravity anomalies and we
conducted detailed analyses of their characteristics by comparing them with the newly determined gravity anomalies, GOCE
EGMs and the basement topography of the ice sheet. The result suggests that the lower gravity anomalies between the coastal
area and the mountains would be due to the thick ice sheet accumulated in the area. The same structure can be found in a wide
area from Dronning Maud Land to Enderby Land, and it is coincident with the area where the ice mass has increased. Although
the reason is not obvious, there might be a relation between the ice sheet flow and the basement topography, in addition to therelation between the snowfall and the mountain topography.

Keywords: gravity anomalies, ice mass movements, Glacial Isostatic Adjustment, absolute gravity measurements, GOCE

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SGD23-08

Room:102A

Time:May 28 09:15-09:30

Absolute gravity measuremt using A10 absolute gravimeter around Gundih gas field for
CCS monitoring
NISHIJIMA, Jun1∗ ; FUKUDA, Yoichi2 ; SOFYAN, Yayan1 ; ITAKURA, Matomu2 ; WAHYUDI, Eko3 ;MATSUOKA, Toshifumi4
1
4Faculty of Engineering, Kyushu University, 2 Graduate School of Science, Kyoto University, 3 Institute of Technology Bandung,
Graduate School of Engineering, Kyoto University

Indonesia government plans to reduce CO2 emissions by 26% from 2005 levels by the year 2020. It is thought that one of
the large quantities of CO2 are released into the atmosphere during production of natural gas at gas processing. And it is oneof the serious problems for the achievement of the national purpose of a total CO2 reduction. This problem can be solved byestablishing a system for carbon dioxide capture and storage (CCS) technology in which the CO2 from natural gas production
is captured and injected into the ground as a means of directly reducing CO2 emissions. The SATREPS project ”Pilot Study for
Carbon Sequestration and Monitoring in Gundih Area, Central Java Province, Indonesia” ,which is funded by JICA and JST, isconducting a research and development of safety storage of CO2 in the subsurface and to establish monitoring technologies in
the Gundih gas field in Central Java, where natural gas production is just started.
We started the absolute gravity measurements using A10 absolute gravimeter (Micro-g LaCoste Inc.) at 6 station. In 2014,
we added 3 station near the candidate place for CO2 injection. The A10 absolute gravimeter is a portable absolute gravimeterproduced by Micro-g LaCoste Inc. It operates on a 12V DC power supply (i.e. vehicle battery). We can measure the absolutegravity using the vehicle battery at the field. We measured 10 sets at each measurement, and 1 set consists of 100 drops. We
observed gravity decrease (30 micro gal) in KTB1. But we did not detect the significant gravity change. We set the soil moisture
meter near KTB1 station in 2013. Though we could not get the data for a long time, but we got about 2 month soil moisture data.
Based on this data, we estimated the gravity effect caused by soil moisture change.
We predicted the amount of gravity changes caused by CO2 injection based on the results of CO2 injection simulation. We
will report the result of the prediction.
Keywords: CCS, Micro-Gravity Monitoring, Absolute Gravity Measurements

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SGD23-09

Room:102A

Time:May 28 09:30-09:45

Gravimetrical vertical array observation -the 2014 fiscal yearTANAKA, Toshiyuki1∗ ; HONDA, Ryo1
1

Tono Res. Inst. of Earthq. Sci.

The gravimetrical vertical array, as we call it here, is to suppress the rainfall disturbance with establishing two gPhone gravimeters across the unconfined groundwater surface using the Mizunami Underground Laboratory (MIU). In the 2014 fiscal year, we
set up gPhone#130 in the refuge area of the 100m-deep sub-stage (sub-stage is a horizontal tunnel between the Main and Ventilation shafts) and gPhone#90 on the ground surface in the measuring room of the Mizunami Geoscience Academy, and haveaccumulated data without bad effects of blasting for construction works as those of years past. The sensor drift of #130 is dominated by nonlinear fluctuations because of high-noise level environment due to drainage equipments and elevator machines. The
one of #90 is almost linear, and we will be able to evaluate the drift rate by using an absolute gravimeter. As for the atmosphericpressure belowground, the difference from the one aboveground becomes larger, the deeper the observed depth is. Therefore,
it is necessary to investigate the reduction methods, both sensor drift and atmospheric disturbance for the sake of sub-microGal
variations. In this presentation, we demonstrate the attempt to decrease the nonlinear drift using non-parametric modeling and toassess atmospheric disturbance based on the MANAL atmospheric model by the Japan Meteorological Agency.
Acknowledgements: This work is supported by a promotion grant for the establishment of the underground research facility of
the Agency for Natural Resources and Energy, Minister of Economy, Trade and Industry. We thank the JAEA for the cooperationof observations (especially Mr. Y. Aoyagi).
Keywords: continuous gravity measurement, gravimeter, inland water, rainfall, atmospheric correction, measuring method

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SGD23-10

Room:102A

Time:May 28 09:45-10:00

Independent component analysis of gravity data observed by gPhone gravimeters
ITAKURA, Matomu1∗ ; FUKUDA, Yoichi1 ; WAHYUDI, Eko januari2 ; KAZAMA, Takahito1
1Graduate School of Science, Kyoto University, 2 Bandung Institute of Technology

We tested ICA (Independent Component Analysis) for detecting the gravity signals due to various geophysical phenomena.
ICA is one of the multivariate analysis methods that decomposes mixed data into uncorrelated components assuming that theoriginal signals are non-Gaussian. Thus far, it has been mainly used for the researches of sound and brain waves because thosesignals are uncorrelated and non-Gaussian.
Since the signals of gravity changes also can be considered non-Gaussian, we tried to separate those signals using ICA. Using
pseudo gravity data sets that were composed by mixing sinusoid waves with different periods, we first conducted numerical tests
to decompose the signals. The results showed that the signals can be separated if the length of data is enough longer than its
wavelength. However the separation was not satisfactory in the following cases; the signals was shorter than their wavelength,
and the signals contained trends. In those cases, the separation can be improved by removing the trend components in advance.
Based on these results, we applied ICA for the analysis of the gravity data obtained by three gPhones #123, #126 and #127 at
a gravity base station (Kyoto A) in Kyoto University. The observations were conducted from January to February, 2014 and thedata period is 300 hours. The Earth tide signals were removed in advance by using BAYTAP-G program, and the instrumental
drift for each gravimeter was corrected by fitting an exponential functions. Since we did not correct the effects of atmosphericpressure, the residual gravity signals, which were used as the input data for ICA analysis, may contain the atmospheric, trends
and other common effects. The results of ICA show the effects of the atmospheric pressure and trends have been detected with
P-P amplitudes of 5.8∼16.0 micro-Gal and 3.5∼14.8 micro-Gal, respectively. Moreover the correlation coefficient between theatmospheric components and the data observed by a barometer was 0.7. However the estimated amplitudes varied within thefactor of three, although the reason was not clear.
Keywords: Independent Component Analysis, gravity

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SGD23-11

Room:102A

Time:May 28 10:00-10:15

Effect of horizontal acceleration on the superconducting gravimeter at Ishigakijima
IMANISHI, Yuichi1∗ ; NAWA, Kazunari2 ; TAMURA, Yoshiaki3 ; IKEDA, Hiroshi4 ; MIYAJI, Takeshi3
1

ERI, The University of Tokyo, 2 AIST, 3 NAOJ, 4 University of Tsukuba

In 2012, we started gravity observations using a superconducting gravimeter (SG) at Ishigakijima island, near the East China
Sea, with the main purpose being detection of possible gravity changes associated with the long-term slow slip events beneaththe Yaeyama Islands. Since then we have been faced with various kinds of unexpected problems, which may be peculiar to
the natural conditions of such an oceanic island. Among them is the apparent correlation between the ground noise level andthe DC offsets of gravity. The amount of gravity changes, as typically observed when typhoons approach the island, reaches
about 2 microgals (gravity increasing), comparable to (or larger than) the possible magnitude of slow slip signals. Here wetry to interpret this phenomenon not as true gravity signals but as apparent changes originating from nonlinear responses of
the gravity sensor. The site is a VLBI station belonging to National Astronomical Observatory Japan, and movements of the
20-meter antenna cause almost monochromatic (˜5 Hz) ground noise. Such an event is accompanied with a positive offset ofgravity signals in the SG. Analysis of records of seismometers we installed at the same station revealed that gravity changes areproportional to the spectral power of horizontal components of ground motion. This fact indicates that a crosstalk between thevertical and horizontal components of the gravity sensor becomes evident when the level of ground motions is extremely high.
A similar mechanism may be applicable to the effect of the enhanced level of 5-second period ground motions on gravity in very
bad weather conditions.
Keywords: superconducting gravimeter, slow slip, Ishigakijima, horizontal acceleration

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SGD23-12

Room:102A

Time:May 28 10:15-10:30

Hydrological disturbances on gravity at Ishigakijima and experiments for their monitoring
NAWA, Kazunari1∗ ; IMANISHI, Yuichi2 ; ITO, Shinobu1 ; TANAKA, Yoshiyuki2 ; TAMURA, Yoshiaki3 ;MIYAKAWA, Ayumu1 ; KAZAMA, Takahito4 ; MIYAJI, Takeshi3 ; OKUDA, Takashi5 ; YAMAYA, Yusuke1 ;IKEDA, Hiroshi6 ; SUGIHARA, Mituhiko1
1Geological Survey of Japan, AIST, 2 Earthquake Research Institute, Univ. Tokyo, 3 National Astronomical Observatory, 4 Kyoto
University, 5 Nagoya University, 6 Tsukuba University

In 2012, we started continuous gravity observation using a superconducting gravimeter (SG) at the VERA Ishigakijima stations, to detect the signal of long-term slow slip that occurs beneath the Yaeyama Islands. Although there are short missing datacaused by a power failure (e.g. by typhoon), we have almost continuously acquired the SG data. However, it is not easy toidentify the signal originating from the slow slip events, mainly because the effects of the atmosphere, the ocean and the underground water on gravity are correlated with each other in a complicated manner. In addition, microseisms with large amplitude
appear to cause nonlinear responses of the gravimeter (Imanishi et al., this meeting). The hydrological effects are regarded as
most important, but it is difficult to model them. For the further study of local hydrological gravity disturbances, we newly
installed profile-type soil moisture meter and seismometers. In addition, we are planning seismic exploration around the VERA
Ishigakijima station. On the SG, we replaced the compressor in August 2014, then, in January 2015, we replaced the refrigerator
and carried out the liquid helium refill. Just before this liquid helium refill work, we carried out parallel observation with anabsolute gravimeter FG5(#217) and the SG. We will also talk about these maintenances.

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SGD23-P01

Room:Convention Hall

Time:May 27 18:15-19:30

Development of new geoid model of remote island of Japan
KOJIMA, Hideki1∗ ; MIYAHARA, Basara1 ; NEMOTO, Satoru1 ; ITOU, Jyunichi1 ; KODAMA, Tokurou1 ;KUROISHI, Yuki1
1

GSI of Jpan

Geospatial Information Authority of Japan released new geoid model of Japan, ”GSIGEO2011”, which consistency with survey
results is greatly improved compared with the former model, covering all Japan islands except the remote islands, on April 2014.
The GSI has developed new geoid model for the remote islands and this poster will report the result of the development.
The model has been developed for each islands by adjusting the latest gravity geoid model of Japan, ”JGEOID2008”, to fit
actually measured geoid undulations, which are determined from the results of GNSS and leveling survey. The methods for the
adjustments are : 1) bias method which expresses spatial distribution of differences between the measured geoid heights andJGEOID2008 (geoid undulation) as a single offset, 2) plane adjustment method which expresses distribution of geoid undulation
in a simple inclined plane, 3) GMT method which expresses distribution of geoid undulation in a surface estimated by GMT
green spline module. The most appropriate method is selected from the three methods depending on a number and density of
input geoid undulations.
Almost all islands have their own height origin determined for each island. Therefore, in order to keep consistency with theheight origin for the island, we have developed models for each island unless a distance between adjacent islands is too short todivide a model into two models.
Ellipsoidal heights of geoid undulation points, which are essential for calculating measured geoid heights, are recalculated if
the heights were calculated before 2004 because all of ellipsoidal heights of GNSS-based control stations, which are used as
reference stations for GNSS analysis, were recalculated on 2004. The consistency between ellipsoidal heights is improved byapplying GNSS antenna phase center variation models which were created from calibration by the GSI.
Release of the new geoid model for the remote islands enables orthometric height determination by GNSS survey in a precisionof third-order leveling over the nation including the remote islands. It is expected that this leads improvement in efficiency on
survey work.

Keywords: GSIGEO2011, geoid, survey results, remote island

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SGD23-P02

Room:Convention Hall

Time:May 27 18:15-19:30

Improvement of the Gravity database of Kanazawa University
HONDA, Ryo1∗ ; SAWADA, Akihiro2 ; HIRAMATSU, Yoshihiro2
1

Tono Research Institute of Earthquake Science, 2 Nat. Sys. College of Sci. and Eng., Kanazawa Univ.

The gravity database of Kanazawa University is now available on web (Honda et al., 2012, J. Geod. Soc. Japan). The terrain
correction for the gravity data is based on Honda and Kono (2005, J. Geod. Soc. Japan) applying 50 m gridded topography
data, which is based on various DEM, including sea data published by Japan Oceanographic Data Center, Japan Coast Gurad.
Recently, 10 m DEM published by Ministry of Land, Infrastructure, Transport and Tourism is available, which covers all overthe country. We refined our correction routine to apply the fine DEM. The terrain gravity correction, especially on mountainous
region, improved by this application. We report our new correction routine with the refined gravity anomaly map.
This research is promoted by the Grant-in-Aid for Scientific Research (C), No. 26400450.

Keywords: Gravity Anomaly, Database

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SGD23-P03

Room:Convention Hall

Time:May 27 18:15-19:30

Minus anomaly region of gravity in Hyuganada and place that sinking-slab-block tears
off shallow part are corresponding
MASE, Hirofumi1∗1none(Please refer to the figure)
In convergence zones, high temperature bodies are formed diagonally-on-and-under the plate of low temp. and the bodies are
drawn each other. The mantle wedge and the plate, get on the high temp. body that heads westward from the east, head westward.
And, they are placed by the high temp. body that heads eastward from the west and compressed. I think this is the main springand structure in it. I explained in each respect of the theory, experiment, and application.(1)(2)(3),etc.
This time, I thankfully used (4) to be able to understand tomography data of 3D in seamless. And I thankfully used (5) about
gravity chart(Bouguer anomaly). I have been interested in the existence of minus anomaly region of gravity where with center in
Hyuganada(5). Result of the research is going out and I want to report. (the minus anomaly region of gravity:The Region)
The Region is divided roughly into the one in prefecture northern part and the prefectural boundary, and the one in Hyuganada.
The latter has the plain center like eye and the long-drawn tail to the south and is impressive. The south end of ,the subducting
slab(The SS), is exactly formed in the eye. Pulling Hot1 and Hot2 against each other is shown by black pair arrows in each
Section. (Names of high temp. bodies, etc. are naming only of here.) Bearing capacity of land and intrusive pressure generated
along with it are shown by pink arrows.
In Section 1-1’,2-2’, Hot1 invades under the land to the east to be deep and is pulled against each other again there with
Hot2. The black arrows are mainsprings that wring and dent or thin The SS. Pressure in the invaded part rises and The SS isdepressed(blue arrow). And the invaded part extends vertically. By the result of this calculation of going out and entering of
density, The Region in the prefecture northern part and the prefectural boundary might exist.
It is thought that the sinking-block is formed and separates from The SS by the above-mentioned action. On the west side,
it is divided into parts from the depth in the west due to the crack(blue broken line) and slips. On the east side, tightening andpull-tearing off(green arrow) are generated in shallow area(Hyuganada). Vertical subsidence of the sinking-block is understoodunderground in the whole area of Miyazaki Prefecture. Section 1-1’–9-9’ are like fixed point scene sending animated cartoon ofthis change.
The site of pull-tearing off and separation(The Site) is in the Miyazaki Prefecture central part offing and is corresponding to thepeak of The Region(Section 4-4’–7-7’,a-a’). By pull-tearing off action, for hanging down part of The Site, the material is pulled
out under the west, the shape is transformed into Rohto type. And, I think that the generation of the density reduction is a causeof the gravity anomaly. End of pull-tearing off and complete separation have already been generated in the southern part(Section
8-8’,9-9’). However, the place is still in The Region and the tail expands to the south. The peak of the gravity anomaly came
like the shadow along with The Site that keeps going north from the south and arrives now. Even if The Site passes, the gravity
anomaly of the place remains as a track (tail) because it does not improve at once.
(1)Mase/SSJ2010/P3-47 (2)Mase/JpGU2012/SCG67-P06 (3)Mase/SSJ2014/S03-P01(4)AIST/Visualization system for subsurface structures/tomography data by Abdelwahed and Zhao (2007)dVp(5)AIST/same to (4)/gravity chart(Bouguer anomaly)

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