The Burris Gravity Meter (TM) manufactured by ZLS Corporation, Austin/Texas, USA, is based on the invention of L&R (L. LaCoste and A. Romberg): The ZLS (zero-length spring). A digital feedback system (range of about 50 mGal) is used to null the beam. Now, more than 120 gravity meters of this make exist worldwide and are used successfully in exploration, volcanology, geodetic work and surveying. The sensor is made of the well-known (L&R) metal-alloy zero-length spring providing a low drift characteristic. The drifts observed are comparable to L&R gravimeters and are less than 0.3 mGal per month, which is much lower than the drifts known for the fused quartz sensors. The dial is calibrated every 50 mGal over the entire 7000 mGal meter range. Since the gravity value is determined at these points, there are no periodic errors. By a fourth heater circuit temperature effects are totally avoided. The gravity meter is controlled via Bluetooth (R) either to a handheld computer (tablet) or a notebook computer. The feedback responds with high stability and accuracy. The nulling of the beam is controlled by the UltraGrav (TM) control system which incorporates an inherently linear PWM (pulse-width modulated) electrostatic feedback system. In order to improve the handling of the gravimeter we have developed two Windows based programs: AGESfield for single measurements and AGEScont for continuous readings. (C) 2018 Institute of Seismology, China Earthquake Administration, etc. Production and hosting by Elsevier B.V. on behalf of KeAi Communications Co., Ltd.

With strainmeters the observation of crustal deformation is possible with a resolution better than 10−9 m. At the Geodynamic Observatory Moxa in Thuringia/Germany an assembly of strainmeters of different types is recording deformation. Deformation mainly results from the tidal forces of sun and moon acting on the Earth, but also comes from seismic wave propagation or regional and local sources. Here we describe the results of an analysis of five time-series, each spanning 482 days, obtained from the different instruments and areal strain. We focus on the Earth tides but also look on the resonance of the Earth’s core to tidal forcing, the Nearly Diurnal Free Wobble. Even if not all five time-series show the resonance, its finding, especially in strain data, confirms the high data quality and sensitivity of the instruments. The analysis of the strainmeter data shows the comparability of the data from the different instruments as well as the good data quality connected to the very low noise level at the Geodynamic Observatory Moxa. Comparison with ocean loading shows that strong effects from local conditions like topography or rock inhomogeneities exist.

Tilt meters are a widely used tool for monitoring long-term and small-scale deformations. Therefore, they are perfectly suited to test potential subsurface waste repositories. Since November 2005 a high sensitive tilt meter of the ASKANIA-type is recording at a distance of 300m from Mizunami Underground Research Laboratory, where two vertical shafts are under construction. During the construction of those shafts large pumps were used to reduce the groundwater level, leading to two large-and several small-scale pore pressure induced tilt signals. Due to the fault system nearby, the tilt direction does not coincide with the direction towards the pump as would be expected in homogeneous media. In this study we analyze the main surface tilt direction caused by pore pressure induced deformation. Our results show two main directions which are both nearly perpendicular to the fault. Also, the long-term signals show a high correlation with the short-term pore pressure induced tilt signals.

It is well known that the quality of gravity modelling of the Earth’s lithosphere is heavily dependent on the limited number of available terrestrial gravity data. More recently, however, interest has grown within the geoscientific community to utilise the homogeneously measured satellite gravity and gravity gradient data for lithospheric scale modelling. Here, we present an interdisciplinary approach to determine the state of stress and rate of deformation in the Central Andean subduction system. We employed gravity data from terrestrial, satellite-based and combined sources using multiple methods to constrain stress, strain and gravitational potential energy (GPE). Well-constrained 3D density models, which were partly optimised using the combined regional gravity model IMOSAGA01C (Hosse et al. in Surv Geophys, 2014, this issue), were used as bases for the computation of stress anomalies on the top of the subducting oceanic Nazca plate and GPE relative to the base of the lithosphere. The geometries and physical parameters of the 3D density models were used for the computation of stresses and uplift rates in the dynamic modelling. The stress distributions, as derived from the static and dynamic modelling, reveal distinct positive anomalies of up to 80 MPa along the coastal Jurassic batholith belt. The anomalies correlate well with major seismicity in the shallow parts of the subduction system. Moreover, the pattern of stress distributions in the Andean convergent zone varies both along the north–south and west–east directions, suggesting that the continental fore-arc is highly segmented. Estimates of GPE show that the high Central Andes might be in a state of horizontal deviatoric tension. Models of gravity gradients from the Gravity field and steady-state Ocean Circulation Explorer (GOCE) satellite mission were used to compute Bouguer-like gradient anomalies at 8 km above sea level. The analysis suggests that data from GOCE add significant value to the interpretation of lithospheric structures, given that the appropriate topographic correction is applied.

We use records from the East Thuringian Seismic Network (OTSN, Ostthuringer Seismisches Netzwerk) to characterize the site response for each station, and to analyze the scope and limits of the Rayleigh modeling for H/V spectral ratio. The stations considered in this work can be classified by their seismic response as hard rock sites or as sites with some site effect. From these results we propose velocity models based on Rayleigh modeling (theoretical Rayleigh wave ellipticity).Our results show that for locations affected by site effects the H/V spectral ratio can be modeled by the theoretical ellipticity of layered velocity models. For hard rock sites the spectral ratio is rather flat and the modeling with the theoretical ellipticity was not very clear. This may be explained by the fact that for hard rock sites the conditions for a clear fundamental frequency associated with S-wave resonance, and therefore with Rayleigh wave ellipticity, are not fulfilled.

Within the Italian Antarctic research programme repeated GPS-measurements are being carried out at well installed points in the area of Northern-Victoria-Land (NVL), Antarctica, called VLNDEF: Victoria Land Network for Deformation Control. Although the deformations obtained over a period of 4 years are quite small we consider micro-gravity measurement a suitable complement for geodynamic research. Since the German Federal Institute for Geosciences and Natural Resources (BGR) is active in that area as well, until the year 2010 performing nine expeditions comprising geological and geophysical work, we used the offer to join expedition GANOVEX X during the season 2009/2010. With three gravimeters 13 points of the Italian network near the German station Gondwana were observed. The advantage of such measurements is that they do not require topographic corrections. Thus, the instrumental resolution and the measurement conditions, resp., are the limits for the resolution and accuracy of the measurements. In order to receive a reliable data base we used three well calibrated gravimeters in parallel and repeated the measurements several times. Local effects due to changes of the ice cover and snow fall are below the achieved measurement accuracy, because the points are so exposed that local effects are negligible. Although the elevation differences up to more than 2,700 m are quite strong, the results reveal the feasibility of these measurements in that area: The obtained standard deviations are in the order of ±10 to ±20 μGal.

The aim of this work is the better understanding of geophysical processes in subduction zones by Finite element modelling. Here we study the effects of various parameters on the deformation and stress field. The tested parameters are the friction coefficient, convergence obliquity, bending of the subduction zone, realistic geometry and visco-elasticity. Increasing the friction coefficient from 0.0 to 0.4 increases the compression by 28 %. For both friction coefficients obliquity leads to higher compression compared to straight convergence. Comparison of the model results with real topographic data reveals considerable analogies even if crustal structure is generalised. To obtain a more realistic structure for the lithosphere we adopted the geometry from well constrained density models. For these models we chose the region in the South American subduction zone around Iquique in North Chile. Including viscosity in the models has a large effect on stress and strain. In a pure elastic model stress and strain develops nearly linear. In contrast curves for the visco-elastic models show a stress maximum and a zone of maximum curvature for the strain. The stress pattern agrees well with the earthquake distribution.

The GRACE (Gravity Recovery and Climate Experiment) satellite mission provides global time-series of the Earth's gravity field. In view of limited resolution and noise from the GRACE data, various filtering techniques have been developed to extract an optimal signal. There is no conclusion on the best filter method so far, however. On the other hand, terrestrial gravity observations from superconducting gravimeters (SGs) provide variations of the gravity field with very high accuracy and time resolution, but only at single points. The aim of this study is to compare GRACE-derived temporal gravity variations with gravity time-series within a network of six Central European SG stations. Empirical orthogonal functions (EOF) analysis was applied to detect common signal characteristics over a 3 yr period (2004–2006). rms Differences between the time-series of several GRACE solutions amount to 60 per cent of the rms variability of the individual data sets. The rms differences between the SG and GRACE time-series are about 70 per cent of the rms value of the SG observations. The best agreement between SG and GRACE is obtained when using a Gaussian filter with filter lengths of 800–1250 km for the GRACE data. With the EOF analysis, a common regional signal can be deduced from all gravity data sets. Nevertheless, differences in the first EOF among the GRACE solutions were up to 40 per cent, and differences of up to 50 per cent were found between the SG-based terrestrial and the GRACE-based satellite observations.

Time variable gravity field models derived from the satellite mission GRACE have been demonstrated to be consistent with water mass variations in the global hydrological cycle. Independent observations are provided by terrestrial measurements. In order to achieve a maximum of reliability and information gain, ground-based gravity observations may be deployed for comparison with the gravity field variations derived from the GRACE satellite mission. In this context, the data of the network of superconducting gravimeters (SG) of the 'Global Geodynamics Project' (GGP) are of particular interest. This study is focused on the dense SG network in Central Europe with its long-term gravity observations. It is shown that after the separation and reduction of local hydrological effects in the SG observations especially for subsurface stations, the time-variable gravity signals from GRACE agree well with the terrestrial observations from the SG station cluster.Station stability of the SG sites with respect to vertical deformations was checked by GNSS based observations. Most of the variability can be explained by loading effects due to changes in continental water storage, and, in general, the stability of all stations has been confirmed.From comparisons based on correlation and coherence analyses in combination with the root mean square (RMS) variability of the time series emerges, that the maximum correspondence between the SG and GRACE time series is achieved when filtering the GRACE data with Gaussian filters of about 1000 km filter length, which is in accordance with previous publications.Empirical Orthogonal Functions (EOF) analysis was applied to the gravity time series in order to identify common characteristic spatial and temporal patterns. The high correspondence of the first modes for GRACE and SG data implies that the first EOF mode represents a large-scale (Central European) time-variable gravity signal seen by both the GRACE satellites and the SG cluster. (C) 2011 Elsevier Ltd. All rights reserved.

In this paper we discuss the first results of a gra vity tidal record obtained with the new gravity meter manufactured by the company ZLS (Zero-LengthSpring Corp.). This is also the first record of this kind in a station in Azerbaijan. And we discuss the results with regard to the dynamics of the Earth-Moon system and the deformati on of the Earth caused by tidal forces and regional contemporary movements and deformation s. The gravimeter is installed in the geodynamic stati on Shaki, Azerbaijan, operated by the Institute of Geology of the National Academy of Sci ences of Azerbaijan. The data covers the period of 2010-2011 and was processed in the Instit ute of Geosciences, Friedrich-SchillerUniversity of Jena, Germany.

The spatial resolution and quality of geopotential models (EGM2008, EIGEN-5C, ITG-GRACE03s, and GOCO-01s) have been assessed as applied to lithospheric structure of the Andean and Central American subduction zones. For the validation, we compared the geopotential models with existing terrestrial gravity data and density models as constrained by seismic and geological data. The quality and resolution of the downward continued geopotential models in the Andes and Central America decrease with increasing topography and depend on the availability of terrestrial gravity data. High resolution of downward continued gravity data has been obtained over the Southern Andes where elevations are lower than 3000 m and sufficient terrestrial gravity data are available. The resolution decreases with an increase in elevation over the north Chilean Andes and Central America. The low resolution in Central America is mainly attributed to limited surface gravity data coverage of the region.To determine the minimum spatial dimension of a causative body that could be resolved using gravity gradient data, a synthetic gravity gradient response of a spherical anomalous mass has been computed at GOCE orbit height (254.9 km). It is shown that the minimum diameter of such a structure with density contrast of 240 kg m(-3) should be at least similar to 45 km to generate signal detectable at orbit height. The batholithic structure in Northern Chile, which is assumed to be associated with plate coupling and asperity generation, is about 60-120 km wide and could be traceable in GOCE data. Short wavelength anomalous structures are more pronounced in the components of the gravity gradient tensor and invariants than in the gravity field.As the ultimate objective of this study is to understand the state of stress along plate interface, the geometry of the density model, as constrained by combined gravity models and seismic data, has been used to develop dynamic model of the Andean margin. The results show that the stress regime in the fore-arc (high and low) tends to follow the trend of the earthquake distributions. (C) 2011 Elsevier Ltd. All rights reserved.

We propose a novel methodology for separation of potential field sources and its 3D inversion. New approaches are developed to separate sources: i) in depth using a succession of upward and downward continuation; ii) in the lateral direction by means of approximation with the field of 3D line segments; iii) according to density and magnetization contrast based on pseudo-gravity calculation. Our original inversion algorithms allow the recovery of unknown 3D geometry both for a restricted body of arbitrary shape and for a contact surface. For the first time, we apply our algorithms to joint inversion of gravity and magnetic data for a large area (the Thuringian Basin in central Germany). We separate in depth sources of both gravitational and magnetic anomalies for the whole territory of Thuringia and compare corresponding components. A 3D model of the main sources is presented based on approximation with 3D line segments and their further transforming into a restricted body or a contact surface with the same field.

The 3D inversion method based on local corrections has been introduced by Prutkin to invert potential field data. It has been applied to gravity data inversion on local, regional, and global scales. Here we introduce the application of this method to invert temporal gravity changes. The inversion procedure is demonstrated by a case study on gravity changes observed at the Mayon stratovolcano between campaigns spanning a period of 1992–1996. Residual gravity changes are compiled from the observed ones. No significant surface deformation was observed within the accuracy of the campaign GPS measurements during the considered period. Residual gravity changes were first inverted in terms of sources represented by 3D line segments. The line segment approximation facilitates the second step of the iterative non-linear inversion based on local corrections. In the second step, the residual gravity changes were inverted in terms of 3D star-convex homogenous bodies representing sources of subsurface mass/density changes. Published geological evidence indicates a shallow magma system at Mayon. The absence of significant deformation accompanying the gravity changes indicates that this system was nearly open during 1992–1996. We hypothesize that the sources of the gravity signal represent mass transport, namely injection of magma into voids of the shallow system. Inversion results for campaign differences 3–1 and 4–1 are presented. For both epochs the inversion results in a source located at a depth of about 4.4km (±0.3km) below sea level. The mass of injected magma was estimated at 0.35 (±0.10)MU and 0.12 (±0.04)MU for the two epochs, respectively. We also compare our results with previous interpretations of the same data.

The Tien Shan in Central Asia is the largest intracontinental mountain range in the world, but it is 1500 km away from the collision zone between the Indian and Eurasian plates. This region has been and still is the focus of numerous geoscientific studies, mainly because of its evolutionary history and its unique position in the Eurasian lithosphere plate. So far, mainly seismological data have been used to explore the origin of and ongoing seismic activity in this region, but only one study has investigated terrestrial gravity data. In this study, a new gravity data set, EGM2008, is used to determine the crust‐mantle boundary (Mohorovičić discontinuity, Moho) of the Tien Shan using inversion of gravity data. In addition, an isostatic Moho is calculated from topographic data, which by comparison to the results of the gravity inversion illuminates the effects of isostatic compensation. The results of the gravity inversion generally agree with results of previous seismic studies and indicate that the Tien Shan has a mountain root with a thickness of about 75 km. Furthermore, the Moho is shallow under the basins, e.g., in the Tarim and Ili basins. The comparison with the isostatic Moho indicates an over‐compensation of the orogen and an under‐compensation of the basins. The over‐compensation results from the former subduction of the Tarim Basin terrane in the south. The under‐compensation of the Tarim Basin is generated by support of the terrane between the Tien Shan in the north and the Pamir mountains, Tibet and Himalayas in the south.

Gravity records include a wide spectrum of signals based on mass changes in the Earth's crust. Today, the detectable amplitudes of the signals of interest become smaller and smaller (e.g., hydrological effects). From this it follows that the accuracy and resolution of measurements must be very high and the noise level as low as possible. In this study, the influence of the temperature variations as noise signal in the gravity records was investigated. Therefore, two 215 day time series of the LaCoste and Romberg gravity meter ET18 in the broadband Geodynamical Observatory Moxa were analyzed and compared. Each time series was recorded in another room. The first room is characterized by a temperature variation of ±4°C per year. The second room has a constant temperature of 19°C. As reference data, the parallel recorded time series of the superconducting gravity meter (SG) CD‐034, installed in the temperature‐stabilized room were used. The result of this study shows a clear influence of temperature variation on the noise level in the spectra of the ET18 compared to the SG spectra. Depending on the frequency ranges, the ratios of the noise levels of the ET18 and SG spectra are between 2 and 5. In the frequency range up to 0.01 cph the ET18/SG factor is 2, between 0.01 cph and 0.09 cph the factor is 3, and above 0.09 cph the factor is 5.

High resolution 3D underground model of the seismically active region of Almaty (Kazakhstan)