Gravity Variations Research Articles

Analysis of gravity anomalies in the Ulleung Basin (East Sea/Sea of Japan) and its implications for the crustal structure of rift-dominated back-arc basin

The Ulleung Basin (UB), one of three major basins in the East Sea/Sea of Japan, is considered to represent a continental-rifting end-member of back-arc basin system, but is much less understood compared to the nearby Yamato Basin (YB) and Japan Basin (JB). This study examines the gravity anomalies of the UB since the variation in crustal thickness can provide important insights on the mode of extension during basin opening. Our analysis shows that the Moho depth (from the sea surface) varies from 16 km at the basin center to 22 km at the edges. However, within the central part of the basin, the crustal thickness (not including sediment) is more or less the same (10–12 km), by varying only about 10–20% of the total thickness, contrary to the previous suggestions. Our finding of anomalous but uniformly thick crust is consistent with the recent seismic results from the YB (14 km on average). A mantle residual gravity anomaly high (∼20 mGal) exists in the northeastern part of the UB. This feature is interpreted as the location of maximum extension (slightly thinner crust by ∼1 km). Together with another moderate gravity high to the southwest, the two anomalies form a NNE-SSW line, which corresponds to the direction of the major tectonic structures of the Korean Peninsula. We argue that the a massive magmatic emplacement took place extensively in the lower crust of the UB during the opening, significantly increasing its overall thickness to almost twice as that of the JB where a mid-ocean-ridge style seafloor spreading occurred. Two important post-opening processes took place after the formation of uniformly thick crust: post-rift volcanic intrusions in the north, especially in its northeast sections but had little effect on the residual gravity anomaly itself, and the deflection of crust in response to differential sediment loading towards the south, producing the median high in the basement in response to the flexural bending. We also conducted a simple test to examine what effect the variations in the mantle potential temperature and degree of extension may have on the gravity anomaly. According to our model, the latter case is much more likely to cause the variations in gravity anomaly than the former.

Nonlinear L1 adaptive control of an airplane with structural damage

This paper investigates the design of a novel nonlinear L1 adaptive control architecture to stabilize and control an aircraft with structural damage. The airplane nonlinear model is developed considering center of gravity variation and aerodynamic changes due to damage. The new control strategy is applied by using nonlinear dynamic inversion as a baseline augmented with an L1 adaptive control strategy on NASA generic transport model in presence of un-modeled actuator dynamics, wing and vertical tail damage. The L1 adaptive controller with appropriate design of filter and gains is applied to accommodate uncertainty due to structural damage and un-modeled dynamics in the nonlinear dynamic inversion loop, and to meet desired performance requirements. The properties of the proposed nonlinear adaptive controller are investigated against a model reference adaptive control, a robust model reference adaptive control, and an adaptive sliding mode control strategy. The results clearly represent the excellent overall performance of the designed controller.

Patterns of within-stem variations in wood specific gravity and water content for five temperate tree species

Intensive measurements of basic specific gravity and relative water content of lumens show that within-stem variations strongly depend on species and cannot be summarised through the typical patterns reported in the literature; breast height measurements are not always representative of the whole stem. Knowledge of the distribution of wood properties within the tree is essential for understanding tree physiology as well as for biomass estimations and for assessing the quality of wood products. The radial and vertical variations of basic specific gravity (BSG) and relative water content of lumens (RWC L ) were studied for five species: Quercus petraea/robur, Fagus sylvatica, Acer pseudoplatanus, Abies alba and Pseudotsuga menziesii. The observations were compared with typical patterns of variations reported in the literature. Wood discs were sampled regularly along tree stems and X-rayed in their fresh and oven-dry states. At breast height, BSG was found to clearly increase radially (pith to bark) for two species and to decrease for one species. For F. sylvatica and A. alba, the radial variations of BSG were rather U-shaped, with in particular inner wood areas showing respectively lower and higher BSG than the corresponding mature wood. RWC L increased generally from inner to outer area but wet sapwood was clearly distinguishable only for the coniferous species. Vertical variations of BSG and RWC L were strongly dependant on the species with usually non-linear patterns. The observed variations of BSG were only partially in agreement with the reported typical radial patterns. Despite the vertical variations, the mean BSG of a cross-section at breast height appeared to be a good estimator of the mean BSG of the whole stem (although the difference was statistically significant for coniferous species), whereas breast height measurement of RWC L was not representative of the whole stem.

The influence of the atmospheric front on the readings of the gravimeters and seismographs

Non-tidal variations of gravity are the residual part of the monitoring of the variations after subtraction from them the lunar-solar gravity variations and the drift of the zero point of the gravimeter. Non-tidal variations have a complex morphology and structure. The sources of the non-tidal variations are the intracrustal processes, flows of the charged particles in space and meteor showers. Meteor showers interacting with the Earth’s atmosphere determine the occurrence, development and movement in the atmosphere of the large-scale eddies - cyclones and anticyclones. The atmospheric fronts are distinguished in isolated cyclones. These fronts can influence the measurements of the gravimeters and seismographs.

Mechanical Properties of Cocos nucifera Wood Planted Around Mt. Merapi, Yogyakarta

This study presented test results of mechanical properties of Cocos nucifera wood that were planted around Mt. Merapi, Yogyakarta. The test specimens were obtained from trees that had been exposed to pyroclastic flow during the 2010 volcanic eruption as indicated by dark colour of the outer bark. Test set-up was designed according to ASTM D143-94 and the mechanical properties, which are determined based on the lower 5% exclusion limit, were bending strength, shear strength, dowel bearing strength and compressive strength. Results of the specific gravity measurement showed significant variation of specific gravity between the inner part (close to the pith) and the outer part (far from the pith) in a cross-section. Since mechanical properties generally depend upon specific gravity, it was decided to divide the wood specimens into two groups: specimens from the inner part and specimens from the outer part. Most of the mechanical properties of wood specimens from the inner part, except for bending strength, were found to be much lower than E10 grade of the Indonesian National Standard (SNI). Hence it is not recommended for any structural use. In the case of wood specimens from the outer part, their mechanical properties were as follows: bending strength 83.66 MPa; shear strength parallel to grain 4.41 MPa; dowel bearing strength parallel to grain 40.65 MPa; dowel bearing strength perpendicular to grain 25.88 MPa, compressive strength parallel to grain 37.89 MPa; and compressive strength perpendicular to grain 7.48 MPa. It seemed that the wood specimens from the outer part had excellent mechanical properties especially in bending, but their shear strength is extremely low.

Investigation of Properties of Rubber Wood Related to Solid Wood Flooring

A large scale solid wood flooring factory is to be established in Sri Lanka. On the planning stage of this industry it was found that information on wood properties of local timbers such as Hevea brasiliensis for wood flooring are not available. Hence, the present study has been conducted to gather data on selected wood properties of Rubber wood and how the wood quality changes with growth rate of trees. Hevea brasiliensis 35 year old trees were selected from three size classes: suppressed, co-dominant and dominant. Sample disks were removed at top (80%), middle (50%) and breast height of the log length. Radial variations were also studied at percentage distances from pith to bark. Wood quality was assessed by ring specific gravity. Ring width remained more or less constant from pith towards bark with slight decrease towards the bark indicating the uniform growth rate. However no specific variation was observed in ring specific gravity. This radial variation of growth rate and specific gravity was similar in all three size classes. Application of Rubber wood as solid wood elements for flooring was experimentally assessed by hardness to loads applied to the wood and specific gravity. The mean specific gravity of suppressed, co-dominant and dominant trees were 0.564, 0.629 and 0.631 respectively indicating that the specific gravity of Rubber wood lies within the required standard for flooring which is 0.5-0.75. In the hardness test, it was observed that all three size classes generally show a gradual increase in hardness from pith towards bark. The values of average hardness of suppressed, co dominant and dominant trees were 341 kgf, 405 kgf and 433 kgf, hence co dominant and dominant trees have hardness values above 400 kgf, the standard value for wood flooring. These results indicate that Hevea brasiliensis has wood properties which are within European standard and Indian standard for manufacture of wooden flooring. Keywords: Rubber wood, Flooring, Specific gravity, Hardness

Characteristics of Marine Gravity Anomaly Reference Maps and Accuracy Analysis of Gravity Matching-Aided Navigation.

The variation of a marine gravity anomaly reference map is one of the important factors that affect the location accuracy of INS/Gravity integrated navigation systems in underwater navigation. In this study, based on marine gravity anomaly reference maps, new characteristic parameters of the gravity anomaly were constructed. Those characteristic values were calculated for 13 zones (105°–145° E, 0°–40° N) in the Western Pacific area, and simulation experiments of gravity matching-aided navigation were run. The influence of gravity variations on the accuracy of gravity matching-aided navigation was analyzed, and location accuracy of gravity matching in different zones was determined. Studies indicate that the new parameters may better characterize the marine gravity anomaly. Given the precision of current gravimeters and the resolution and accuracy of reference maps, the location accuracy of gravity matching in China’s Western Pacific area is ~1.0–4.0 nautical miles (n miles). In particular, accuracy in regions around the South China Sea and Sulu Sea was the highest, better than 1.5 n miles. The gravity characteristic parameters identified herein and characteristic values calculated in various zones provide a reference for the selection of navigation area and planning of sailing routes under conditions requiring certain navigational accuracy.

A data-driven model for constraint of present-day glacial isostatic adjustment in North America

Geodetic measurements of vertical land motion and gravity change are incorporated into an a priori model of present-day glacial isostatic adjustment (GIA) in North America via least-squares adjustment. The result is an updated GIA model wherein the final predicted signal is informed by both observational data, and prior knowledge (or intuition) of GIA inferred from models. The data-driven method allows calculation of the uncertainties of predicted GIA fields, and thus offers a significant advantage over predictions from purely forward GIA models. In order to assess the influence each dataset has on the final GIA prediction, the vertical land motion and GRACE-measured gravity data are incorporated into the model first independently (i.e., one dataset only), then simultaneously. The relative weighting of the datasets and the prior input is iteratively determined by variance component estimation in order to achieve the most statistically appropriate fit to the data. The best-fit model is obtained when both datasets are inverted and gives respective RMS misfits to the GPS and GRACE data of 1.3 mm/yr and 0.8 mm/yr equivalent water layer change. Non-GIA signals (e.g., hydrology) are removed from the datasets prior to inversion. The post-fit residuals between the model predictions and the vertical motion and gravity datasets, however, suggest particular regions where significant non-GIA signals may still be present in the data, including unmodeled hydrological changes in the central Prairies west of Lake Winnipeg. Outside of these regions of misfit, the posterior uncertainty of the predicted model provides a measure of the formal uncertainty associated with the GIA process; results indicate that this quantity is sensitive to the uncertainty and spatial distribution of the input data as well as that of the prior model information. In the study area, the predicted uncertainty of the present-day GIA signal ranges from ∼0.2–1.2 mm/yr for rates of vertical land motion, and from ∼3–4 mm/yr of equivalent water layer change for gravity variations.

Landscape-scale water balance monitoring with an iGrav superconducting gravimeter in a field enclosure

Abstract. In spite of the fundamental role of the landscape water balance for the Earth's water and energy cycles, monitoring the water balance and its components beyond the point scale is notoriously difficult due to the multitude of flow and storage processes and their spatial heterogeneity. Here, we present the first field deployment of an iGrav superconducting gravimeter (SG) in a minimized enclosure for long-term integrative monitoring of water storage changes. Results of the field SG on a grassland site under wet–temperate climate conditions were compared to data provided by a nearby SG located in the controlled environment of an observatory building. The field system proves to provide gravity time series that are similarly precise as those of the observatory SG. At the same time, the field SG is more sensitive to hydrological variations than the observatory SG. We demonstrate that the gravity variations observed by the field setup are almost independent of the depth below the terrain surface where water storage changes occur (contrary to SGs in buildings), and thus the field SG system directly observes the total water storage change, i.e., the water balance, in its surroundings in an integrative way. We provide a framework to single out the water balance components actual evapotranspiration and lateral subsurface discharge from the gravity time series on annual to daily timescales. With about 99 and 85 % of the gravity signal due to local water storage changes originating within a radius of 4000 and 200 m around the instrument, respectively, this setup paves the road towards gravimetry as a continuous hydrological field-monitoring technique at the landscape scale.

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

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

Structural variability of the Tonga-Kermadec forearc characterized using robustly constrained geophysical data

Subducting bathymetric anomalies enhance erosion of the overriding forearc crust. The deformation associated with this process is superimposed on pre-existing variable crustal and sedimentary structures developed as a subduction system evolves. Recent attempts to determine the effect and timescale of Louisville Ridge seamount subduction on the Tonga-Kermadec forearc have been limited by simplistic models of inherited overriding crustal structure that neglect along-strike variability. Synthesis of new robustly tested seismic velocity and density models with existing datasets from the region, highlight along-strike variations in the structure of the Tonga-Kermadec subducting and overriding plates. As the subducting plate undergoes bend-faulting and hydration throughout the trench-outer rise region, observed oceanic upper- and mid-crustal velocities are reduced by ∼1.0 km s−1 and upper mantle velocities by ∼0.5 km s−1. In the vicinity of the Louisville Ridge Seamount Chain (LRSC), the trench shallows by 4 km and normal fault throw is reduced by > 1 km, suggesting that the subduction of seamounts reduces plate deformation. We find that the extinct Eocene frontal arc, defined by a high velocity (7.0–7.4 km s−1) and density (3.2 g cm−3) lower-crustal anomaly, increases in thickness by ∼6 km, from 12 to > 18 km, over 300 km laterally along the Tonga-Kermadec forearc. Coincident variations in bathymetry and free-air gravity anomaly indicate a regional trend of northward-increasing crustal thickness that predates LRSC subduction, and highlight the present-day extent of the Eocene arc between 32° S and ∼18° S. Within this framework of existing forearc crustal structure, the subduction of seamounts of the LRSC promotes erosion of the overriding crust, forming steep, gravitationally unstable, lower-trench slopes. Trench-slope stability is most likely re-established by the collapse of the mid-trench slope and the trenchward side of the extinct Eocene arc, which, within the framework of forearc characterisation, implies seamount subduction commenced at ∼22° S.

Long-term dynamics across a volcanic rift: 21 years of microgravity and GPS observations on the southern flank of Mt. Etna volcano

In this paper, an integrated analysis of microgravity and ground deformation measurements at Mt. Etna is performed over a 21-years time span (1994–2014), a period encompassing several flank and summit eruptions. Data were collected along a common gravity and ground deformation network located on the volcano's southern flank to monitor the dynamics of the main volcanic and tectonic processes. Gravity variations have first been corrected for the free-air effect using the vertical deformation and the experimental vertical gravity gradients measured at each station. The free-air corrected gravity changes were then reduced for seasonal fluctuations, mainly imputable to water-table fluctuations, and for high frequency variations (noise).This long-term dataset constitutes a unique opportunity to examine the behavior of Mt. Etna in a period in which the volcano exhibited different styles of activity characterized by recharging, flank eruptions and fountaining episodes at summit craters. The joint analysis highlights common periods in which gravity and deformation underwent contemporaneous changes occurring mainly in the central and eastern stations of the profile. Specifically, it was possible to distinguish three different sectors, showing significant deformation and gravity patterns: a western sector, lying west of the South Rift, a central one between the South Rift and the 1989 fracture zone, and an eastern one lying east of the 1989 fracture system. The data shows that the deflation dynamics accompanying the eruptive phases mainly affect the western portion of the profile, gradually disappearing toward East, where the more constant sliding dynamics dominates. This pattern defines a transition zone corresponding to the sector comprised between the South Rift and the 1989 fracture. Furthermore, it was also possible to detect at least three main magma charging phases in 1996, 2000 and 2011 which preceded and accompanied the onset of intense flank eruptions and lava fountaining activity at the summit craters.

Estimating Jupiter’s Gravity Field Using Juno Measurements, Trajectory Estimation Analysis, and a Flow Model Optimization

Abstract The upcoming Juno spacecraft measurements have the potential of improving our knowledge of Jupiter’s gravity field. The analysis of the Juno Doppler data will provide a very accurate reconstruction of spatial gravity variations, but these measurements will be very accurate only over a limited latitudinal range. In order to deduce the full gravity field of Jupiter, additional information needs to be incorporated into the analysis, especially regarding the Jovian flow structure and its depth, which can influence the measured gravity field. In this study we propose a new iterative method for the estimation of the Jupiter gravity field, using a simulated Juno trajectory, a trajectory estimation model, and an adjoint-based inverse model for the flow dynamics. We test this method both for zonal harmonics only and with a full gravity field including tesseral harmonics. The results show that this method can fit some of the gravitational harmonics better to the “measured” harmonics, mainly because of the added information from the dynamical model, which includes the flow structure. Thus, it is suggested that the method presented here has the potential of improving the accuracy of the expected gravity harmonics estimated from the Juno and Cassini radio science experiments.

Insights on the structure of Lusi mud edifice from land gravity data

Since May 2006, the active Lusi mud eruption has continuously erupted boiling mud. During the early stages of the eruption in 2006, previous gravity studies showed that the piling up of the mud constructed a large edifice that subsides within the unconsolidated sediment especially around a large area over the active crater. After ten years of continuous eruption, the size of the edifice has grown significantly over a surface framed by 10 m tall containment embankments. In 2015 and 2016, several land gravity surveys were carried out to investigate the structure of the mud edifice and the effect of local geological active features. The new residual Bouguer anomaly map, calculated for a reference density of 2670 kg m−3, shows significant changes in the local gravity field in comparison to the previous 2006-gravity map survey. The new data set shows that the gravity decrease is generally restricted along the faulted and fractured zones, around erupting vents, and in the southern part of the mud edifice. Maximum gravity variations reach 1.4 mGal in some areas of the mud edifice. In the region outside the embankment, the gravity reductions are 0.6 mGal E-W and 1.0 mGal N-S. A second vertical derivative analysis of gravity data indicates that the mud edifice continues to pile up and subside mostly in the western and southern part of the edifice. Results of a 3D forward model of a vertical cylinder shape allowed characterising the extent of compacted material along the Watukosek fault system that originates from the neighbouring volcanic arc and crosses the mud edifice. Our results support the hypothesis of local pinched volume of mud ongoing between the subsided and uplifted masses of mud. The density of compacted mud breccia material increases between 16 and 27%. Gravity data also shows that the Lusi mud edifice is built over an extended NW-SE gravity increase, interpreted as a sediment density variation within the basin, and which is parallel to the trend of the Basin.

Acoustic gravity waves and the atmospheric electric field perturbations accompanying them

Data on observations of acoustic gravity waves and variations in the electric field strength in the surface layer of the atmosphere are presented. Analysis of the obtained data shows that synchronous variations in the pressure and electric field strength appear with the passage of a weather front, solar terminator, and in some other cases. It is seen that the amplitude of electric field perturbations is approximately proportional to the amplitude of variation in the pressure. A possible mechanism of generating electric field perturbations during the passage of microbaroms has been considered.

ABNORMAL CHANGES OF THE NON-TIDAL VARIATIONS OF GRAVITY

Non-tidal variations of gravity are the residual part of the monitoring of the variations after subtraction from them the lunar-solar gravity variations and the drift of the zero point of the gravimeter. Non-tidal variations are sometimes of complex morphology and structure. The sources of the non-tidal variations are the intracrustal processes and flows of the charged particles in space. The streams of the charged particles can affect the sensor of the gravimeter. The streams of the charged particles can create a powerful magnetic hydrodynamic (MHD) shocks that cause abnormal changes of gravity. It is necessary to consider the non-tidal variations when carrying out high-precision gravimetric measurements.

The Geoid Slope Validation Survey 2014 and GRAV-D airborne gravity enhanced geoid comparison results in Iowa

Three Geoid Slope Validation Surveys were planned by the National Geodetic Survey for validating geoid improvement gained by incorporating airborne gravity data collected by the “Gravity for the Redefinition of the American Vertical Datum” (GRAV-D) project in flat, medium and rough topographic areas, respectively. The first survey GSVS11 over a flat topographic area in Texas confirmed that a 1-cm differential accuracy geoid over baseline lengths between 0.4 and 320 km is achievable with GRAV-D data included (Smith et al. in J Geod 87:885–907, 2013). The second survey, Geoid Slope Validation Survey 2014 (GSVS14) took place in Iowa in an area with moderate topography but significant gravity variation. Two sets of geoidal heights were computed from GPS/leveling data and observed astrogeodetic deflections of the vertical at 204 GSVS14 official marks. They agree with each other at a \({\pm }1.2\,\, \hbox {cm}\) level, which attests to the high quality of the GSVS14 data. In total, four geoid models were computed. Three models combined the GOCO03/5S satellite gravity model with terrestrial and GRAV-D gravity with different strategies. The fourth model, called xGEOID15A, had no airborne gravity data and served as the benchmark to quantify the contribution of GRAV-D to the geoid improvement. The comparisons show that each model agrees with the GPS/leveling geoid height by 1.5 cm in mark-by-mark comparisons. In differential comparisons, all geoid models have a predicted accuracy of 1–2 cm at baseline lengths from 1.6 to 247 km. The contribution of GRAV-D is not apparent due to a 9-cm slope in the western 50-km section of the traverse for all gravimetric geoid models, and it was determined that the slopes have been caused by a 5 mGal bias in the terrestrial gravity data. If that western 50-km section of the testing line is excluded in the comparisons, then the improvement with GRAV-D is clearly evident. In that case, 1-cm differential accuracy on baselines of any length is achieved with the GRAV-D-enhanced geoid models and exhibits a clear improvement over the geoid models without GRAV-D data. GSVS14 confirmed that the geoid differential accuracies are in the 1–2 cm range at various baseline lengths. The accuracy increases to 1 cm with GRAV-D gravity when the west 50 km line is not included. The data collected by the surveys have high accuracy and have the potential to be used for validation of other geodetic techniques, e.g., the chronometric leveling. To reach the 1-cm height differences of the GSVS data, a clock with frequency accuracy of \(10^{-18}\) is required. Using the GSVS data, the accuracy of ellipsoidal height differences can also be estimated.

The Improved Hydrological Gravity Model for Moxa Observatory, Germany

The gravity variations observed by the superconducting gravimeter (SG) CD-034 at Moxa Geodynamic Observatory/Germany were compared with the GRACE results some years ago. The combination of a local hydrological model of a catchment area with a 3D-gravimetric model had been applied successfully for correcting the SG record of Moxa which is especially necessary due to the strong topography nearest to the SG location. Now, the models have been corrected and improved considerably by inserting several details in the very near surrounding. Mainly these are: the observatory building is inserted with the roof covered by a soil layer above the gravity sensor where humidity is varying, snow is placed on top of the roof and on topography (steep slope), and ground water is taken into account, additionally. The result is that the comparison of the corrected gravity residuals with gravity variations of the satellite mission GRACE, now using RL5 data, shows higher agreement, not only in amplitude but also the formerly apparent phase shift is obviously not realistic. The agreement between terrestrial gravity variations (SG) and the GRACE data is improved considerably which is discussed widely.

Gravity observation at continental borderlands (Russia, Primorie, Cape Shults)

The paper is focused on different kinds of gravity results obtained in Shults Cape Observatory for 2010–2015. Gravity observation is interpreted together with GPS observation data which was obtained from 2012 to 2015 at the same station. The station is situated on Gamov peninsular (42.58° N, 131.15° E, Russia) at the coast of Japan Sea. This region constitutes the eastern boundary of Eurasia. This major continental tectonic feature is associated with a seismic activity, high heat flow and anomalous thickness of earth's crust. The goal of the observation was the investigation of gravity variation with time and seismicity situation monitoring. Gravity observation was developed at special basement by absolute gravimeter (GABL type) and by spring gravimeter (SCINREX CG-5and gPhone type). Tidal models were tested by results of observation with spring gravimeters. Reduction task was solved, as the experimental data received from different points of Shults Cape Observatory was used. Applied reduction coefficient is 203.3 μGal m−1, and agrees with theoretical calculation. Next goal was studying structure of earth's crust by means of gravity models. Gravity anomaly varied from 30 mGal to 46 mGal, which also depend on difference reference system. Experimental results were used for testing of the structure of continental boundary, which also depends on the sea bottom flexion. Thickness of elastic layer was estimated from 12 km to 18 km by using different models.

Absolute Gravity Variation at Sakurajima Volcano from April 2009 through January 2011 and its Relevance to the Eruptive Activity of Showa Crater(＜Special Section＞Sakurajima Special Issue)

Absolute Gravity Variation at Sakurajima Volcano from April 2009 through January 2011 and its Relevance to the Eruptive Activity of Showa Crater(＜Special Section＞Sakurajima Special Issue)