Absolute Gravity Observations Research Articles

Geodetic/gravimetric evidence for mass loss in the subsidence area of Bandung, Indonesia

Land subsidence monitoring in Bandung, Indonesia, was initiated in the 2000 s. However, the monitoring has been limited to geometric observations only, which may restrict the further physical interpretation of the cause of the subsidence. In this study, we combine geometric and gravity observation methods to monitor surface subsidence in Bandung. 63 Synthetic Aperture Radar (SAR) images from Sentinel-1A covering the period of 2014–2020 were used to estimate the mean surface geometric changes. For the gravity observations, a hybrid gravity configuration that incorporates absolute (2008–2014) and relative (2011–2016) gravity observations were used to estimate the gravity changes. We estimated geometric changes of up to − 160 mm/yr, indicating rapid subsidence in the greater Bandung area. We obtained gravity changes ranging between − 56.7 and 40.1 μGal/yr. Upon subtracting the deformation-induced gravity field from the observed field, we produced a residual gravity field that was presumed to be dominated by the groundwater signal, which was then investigated further. We found that the gravity-derived groundwater signal was mainly negative, indicating subsurface mass loss. We further compared the signal with the modeled gravity effect from deep groundwater observations (1996–2008). The median difference between the observed and modeled groundwater gravity signal was estimated to be 2.8 ± 18.0 μGal/yr or equivalent to 0.08 ± 0.55 m/yr in terms of water height if we set the integration cap and groundwater depth to 1.4 km and 150 m, respectively. The discrepancy can be attributed to modeling (simple geohydrological assumption) and measurement (different observation periods and noise) factors. Nevertheless, both measurements indicate that the mass is decreasing due to groundwater depletion, demonstrating the potential of geometric-gravimetric observations to infer sub-surface mass loss.

Constraints on Secular Geocenter Velocity From Absolute Gravity Observations in Central North America: Implications for Global Melting Rates

AbstractLong series of absolute gravity observations at multiple sites provide a direct method of measuring the velocity of the geocenter caused by surface mass transport related to climate change. Annual absolute gravity observations and available GPS vertical data at eight sites in central North America from 1995 to 2010 are used to solve for geocenter velocity while correcting for glacial isostatic adjustment. The precision of the secular gravity trends and GPS heights at our sites, used to estimate geocenter motion, was improved by correcting for local and global water storage attraction and loading. Corrections for the loading and attraction effects of regional ice‐mass loss, the atmosphere and non‐tidal ocean were found to be minimal. Our results provide a direct measurement of the change in geocenter velocity over the time‐interval 2002–2010 compared to the time‐interval 1995–2003 of 0.68 ± 0.28 mm/yr away from North America. This suggests similar velocities in the negative Z (0°N) and positive Y (90°E) directions to those found by other studies.

Gravity yearly transient change around the epicenter of 2022 MS 6.9 Menyuan earthquake, China and seismotectonic implications

The MS 6.9 Menyuan earthquake occurred in the northeastern Tibetan Plateau on 8 January 2022. High-precision absolute gravity observations provide a unique perspective on seismotectonic feature of strong continental earthquakes. An obvious and coincident gravity increase about 5 years before the Menyuan earthquake with the rate up to 3.94 μGal/yr is observed at four absolute gravity stations within 350 km away from the epicenter. These four stations have been carried out repeat gravity observations by the Crustal Movement Observation Network of China (CMONOC) for more than a decade. The observed gravity changes could not be reasonably explained by the land water storage change nor crustal vertical deformation and thus might be related to the processes in the crust. A disc-shaped equivalent source region with a radius of 175 km is then modeled, based on the residual gravity rates. We find that the seismicity increases gradually in the modeled source region from about 2017 to 2021, similar to the pattern of absolute gravity change. Furthermore, the spatiotemporal distribution of epicenters is consistent with the fluids diffusion model, indicating that this could be related to the redistribution of deep fluid mass. With consideration of the near-surface processes, regional crustal structure, and seismicity, multiple lines of evidence consistently refer to the presence of deep fluids migration before the Menyuan earthquake. Our results suggest that high-precision absolute gravimetry can be used to monitor crustal fluid environment and determine mass changes in the source regions of potential large earthquakes.

Long time series of absolute gravity observations in Kulusuk, southeast Greenland

AbstractThis report contains terrestrial absolute gravity measurements performed near the village of Kulusuk in southeast Greenland. It represents an exceptionally long time series of nearly two decades. The measurements began in July 1996 until July 2015. The station is located a few meters beside a permanent GNSS station. The final gravity values (g‐values), more precisely the accelerations due to gravity, are listed along their associated uncertainties. A description of the station, a short explanation on the absolute gravimeter, and the data processing are presented.

Hydrologic changes of in-situ gravimetry

Inter-seasonal and geodynamics-related gravity changes are important geoscientific signals that are extractable from gravimeter observations after removing background information as local hydrology gravity effect. With two superconducting gravimeters (SGs: OSG-053 and iGrav-007) located in different tectonic units, continuous global navigation satellite system data and absolute gravity observations, Wuhan, China, is an ideal location for investigating the effects of gravity resulting from significant local hydrology mass variations. We have processed approximately 26 months of gravity data collected from the SGs in Wuhan and obtained residuals of [Formula: see text] for OSG-053 and [Formula: see text] for iGrav-007. The hydrological observations indicate an estimated gravity increase of [Formula: see text] near iGrav-007, which mainly results from an increase in unconfined water level with an aquifer-specific yield of approximately 0.1. However, the gravity changes around OSG-053 are mainly from soil moisture and reach −[Formula: see text]. The soil type, thickness, and water content parameters are obtained from hydrogeological surveys and drilling data. The deep confined water level rises by 2.5 m, which introduces a [Formula: see text] gravity variation with a specific storage approximately 0.00001 from the field unsteady-flow pumping test. The modeled gravity is approximately [Formula: see text] around OSG-053 and [Formula: see text] around iGrav-007, in accordance with the observed gravity variations. The difference in gravity changes between the two SG observations can be explained by different local water storage environments. Our results suggest that unconfined and soil water significantly impact the in-situ gravimetry, and that further detailed hydrogeological surveys are required. A combined investigation of gravity and water levels can be a useful approach for monitoring aquifer storage conditions and groundwater management.

Reducing hydrological disturbances in absolute gravity observations by combining global hydrological models with a regional run-off model

SUMMARYSince the beginning of the 1990s, absolute gravity has been observed at several locations in Norway with FG5-type instruments to investigate the temporal gravity changes due to glacial isostatic adjustment (GIA). Previous work suggests that some of the estimated secular gravity trends may be affected by remaining unmodelled geophysical effects, such as the effect of local hydrology. In this work, we compute hydrological gravity effects from global hydrological models for the far zone and a combination of regional run-off models and modelling of residual hydrological effects for the near zone. The method developed in this paper is first tested at the geodetic observatory in Wettzell, Germany, where both high-resolution superconducting gravimeter data as well as a regional hydrological model are available. Next, the method is transferred to two Norwegian gravity sites (NMBU and TRYC), with long time-series of frequent absolute gravity observations using FG5-226. At these sites, we investigate the impact of the hydrological gravity correction on data variability as well as estimated secular gravity trends. We find that the data variability is reduced by up to 40 per cent when applying the modelled hydrological gravity effect at TRYC. The reduction is less at NMBU where the amplitude of the hydrological signal and in consequence also the signal-to-noise ratio are smaller. We also note that it is challenging to determine the near zone residual hydrological effects without carefully taking into account the hydrogeological setting of the area for modelling such effects. When utilizing the long corrected absolute gravity series to determine the gravity trends, we find that the estimated trends are not significantly different from the uncorrected observations. However, the uncertainty of the estimated trends is reduced significantly for a limited corrected gravity series. We further suggest repeatability analysis of the absolute gravimeter. From the long time-series at NMBU we find a significant step coinciding with hardware replacement. We find that the fit between observed and modelled secular trends improves when introducing the step. Further analysis of gravity rates at other stations is needed to verify the existence of a real instrumental offset.

Absolute gravity observations in Estonia from 1995 to 2017

Absolute gravity observations in Estonia from 1995 to 2017

Infiltration coefficient, percolation rate and depth-dependent specific yields estimated from 1.5 years of absolute gravity observations near a recharge lake in Pingtung, Taiwan

An efficient underground reservoir management requires reliable hydrogeological parameters, such as infiltration coefficient, percolation rate and specific yield (Sy) values. The cross-well pumping test is a well-known method for determining Sy, but different unsaturated flow models can lead to various Sy results. Heterogeneity in unsaturated and saturated zones can restrict well-dependent methods in estimating these parameters on a regional scale, for which an alternative, gravity-based method is attempted in this study. We established an absolute gravity site at the Wanlong Primary school (WLPS) near a recharge lake (an artificial lake) in the Pingtung Plain and collected 1.5 years of gravity data in 2019–2020. Around a monsoonal rain event in late May 2020, gravity values underwent three stages of changes. The first stage experienced a rapid gravity rise of 18 μgal from infiltrated rain, followed by stable gravity values in the second stage when the infiltrated rain recharged the aquifer, and the third stage showed a persistent gravity increase with rising groundwater level. The gravity-based estimate of infiltration coefficient is 0.84 ± 0.14, and the percolation rate is about 15 m/day, suggesting that WLPS is over a high infiltration region. A depth-dependent Sy profile up to 30 m depth was constructed using gravity and groundwater data. In the dry season, it was found that Sy values are higher at the aquifer depths of 22–28 m than in the shallow part. However, some Sy values determined in the wet seasons are overestimated due to high soil water content (SWC) changes, which induced particularly large gravity changes in the 30-m unsaturated zone of WLPS when the wet season started. This study confirms the advantage of using high precise gravity measurements (at one μgal level) and hydrology records for regional hydrogeological parameter estimation.

Simultaneous calibration of instrument scale factor and drift rate in network adjustment for continental-scale gravity survey campaign

SUMMARY The scale factor of each relative gravimeter must be calibrated both before and after the fieldwork of a terrestrial gravity survey, to reduce uncertainties and ensure high precision. Conventionally, such calibration is a time-consuming process performed following well-established baselines. We propose a new Bayesian method to estimate the scale factor in a hybrid gravity network that includes several absolute gravity observation stations. In this approach, the scale factor is estimated as a hyperparameter using the Akaike Bayesian information criterion and using known absolute gravity stations in the network or/and calibrated instruments as constraints. Testing the sensitivity of the gravity values and the residuals of the gravity difference between two successive stations to the change of the scale factor demonstrates the robustness of this method. We also test the sensitivity of the estimated scale factor in the presence of Gaussian noise and the non-linear instrumental drift rate. Moreover, if the maximum absolute gravity interval is greater than 60 per cent of the range of gravity values in the network, or if the known scale factors of calibrated gravimeters are well calibrated, this approach can provide reasonable estimates of the daily drift rate and the unknown scale factors, where the latter has an error of <3 × 10−5. We apply this approach to real gravity campaign data from Yunnan in China and use a cross-validation method to compare estimated gravity values and corresponding gravity values obtained from absolute gravity observations at the same stations, to validate how the proposed method improves estimation accuracy of the gravity value at each station.

Forty-three years of absolute gravity observations of the Fennoscandian postglacial rebound in Finland

Postglacial rebound in Fennoscandia causes striking trends in gravity measurements of the area. We present time series of absolute gravity data collected between 1976 and 2019 on 12 stations in Finland with different types of instruments. First, we determine the trends at each station and analyse the effect of the instrument types. We estimate, for example, an offset of 6.8 μgal for the JILAg-5 instrument with respect to the FG5-type instruments. Applying the offsets in the trend analysis strengthens the trends being in good agreement with the NKG2016LU_gdot model of gravity change. Trends of seven stations were found robust and were used to analyse the stabilization of the trends in time and to determine the relationship between gravity change rates and land uplift rates as measured with global navigation satellite systems (GNSS) as well as from the NKG2016LU_abs land uplift model. Trends calculated from combined and offset-corrected measurements of JILAg-5- and FG5-type instruments stabilized in 15 to 20 years and at some stations even faster. The trends of FG5-type instrument data alone stabilized generally within 10 years. The ratio between gravity change rates and vertical rates from different data sets yields values between − 0.206 ± 0.017 and − 0.227 ± 0.024 µGal/mm and axis intercept values between 0.248 ± 0.089 and 0.335 ± 0.136 µGal/yr. These values are larger than previous estimates for Fennoscandia.

Status of the International Gravity Reference System and Frame

The increasing importance of terrestrial gravimetry in monitoring global change processes, in providing a reference for satellite measurements and in applications in metrology necessitates a stable reference system reflecting the measurement accuracy achievable by modern gravimeters. Therefore, over the last decade, the International Association of Geodesy (IAG) has developed a system to achieve accurate, homogeneous, long-term global recording of Earth’s gravity, while taking advantage of the potential of today’s absolute gravity measurements. The current status of the International Gravity Reference System and Frame is presented as worked out by the IAG Joint Working Group 2.1.1 “Establishment of a global absolute gravity reference system” during the period 2015–2019. Here, the system is defined by the instantaneous acceleration of free-fall, expressed in the International System of Units (SI) and a set of conventional corrections for the time-independent components of gravity effects. The frame as the systems realization includes a set of conventional temporal gravity corrections which represent a uniform set of minimum requirements. Measurements with absolute gravimeters, the traceability of which is ensured by comparisons and monitoring at reference stations, provide the basis of the frame. A global set of such stations providing absolute gravity values at the microgal level is the backbone of the frame. Core stations with at least one available space geodetic technique will provide a link to the terrestrial reference frame. Expanded facilities enabling instrumental verification as well as repeated regional and additional comparisons will complement key comparisons at the level of the International Committee for Weights and Measures (CIPM) and ensure a common reference and the traceability to the SI. To make the gravity reference system accessible to any user and to replace the previous IGSN71 network, an infrastructure based on absolute gravity observations needs to be built up. This requires the support of national agencies, which are encouraged to establish compatible first order gravity networks and to provide information about existing absolute gravity observations.

Upper mantle density and surface gravity change in Fennoscandia, determined from GRACE monthly data

Precise gravity measurements have been repeatedly observed in Fennoscandia since the 1960-ties, first by relative gravimeters, then by absolute gravimeters, for studying the temporal change of gravity related with the on-going glacial isostatic adjustment (GIA). The results of such studies are vital for understanding GIA processes and tuning GIA and Earth structure models.This study uses monthly repeated data from the twin satellite mission GRACE for 164 months between 2003 and 2016 for estimating the temporal change of surface gravity, its ratio (f) to the land uplift rate as well as the upper mantle density related with the viscous mass flow in the mantle. The maximum negative change of gravity is estimated to −1.8 μGal/yr, and f is estimated to −0.172 ± 0.018 μGal/mm.The solutions for f from the three independent techniques (relative, absolute and satellite gravity observations) were found to agree statistically without significant biases, and they were merged in a joint solution to −0.166 ± 0.004 μGal/mm, corresponding to a mean upper mantle mass flow density of 3402.5 ± 95 kg/m3, which decreases towards the uplift center.

Gravity variations preceding the large earthquakes in the Qinghai-Tibet Plateau from 21st century

Since the beginning of 21st century, there have been 7 large earthquakes in the Qinghai-Tibet Plateau: The Kunlun Mountain Pass M s8.1 earthquake in 2001, the Wenchuan M s8.0 earthquake and the Yutian M s7.3 earthquake in 2008, the Yushu M s7.1 earthquake in 2010, the Lushan M s7.0 earthquake in 2013, the Yutian earthquake M s7.3 in 2014, and the Jiuzhaigou M s7.0 earthquake in 2017. Prior to these earthquakes, the China Earthquake Administration (CEA) had gathered mobile gravity observations over several periods near the epicenter region, obtaining reliable gravity change with time data. In this study, the relationship between gravity variation and these 7 large earthquakes was analyzed using the absolute and relative gravity observations. The results revealed that: (1) The gravity variation fields related to the occurrence of these earthquakes were in response to the movement and change of underground fluid distributed deep in the crust. An enhanced regional stress field leads to deep material migration and transformation, which results in large-scale regional gravity change. (2) Large earthquakes tend to occur in the high-gradient transition zones between positive and negative gravity anomaly regions associated with the boundary of tectonic active blocks. The inflection point of the gravity change isoline is the transition zone between increasing and decreasing material density. The difference in the motions of the increasing and decreasing material is intense, and shear stress easily occurs in the high-gradient zones of the gravity change isoline. This leads to rupture, which then induces earthquakes. (3) The 2001 Kunlun Mountain Pass M s8.1 earthquake occurred near the intersection of the high gradient zone of gravity change and the East Kunlun fault zone on the northern boundary of the Bayan Hara Block; the Wenchuan M s8.0 earthquake in 2008 and the Lushan M s7.0 earthquake in 2013 occurred in the high gradient zone of gravity variation along the Longmenshan fault zone on the eastern boundary of the Bayan Hara block; the 2 Yutian M s7.3 earthquakes in 2008 and 2014 occurred on the 0 value line of the high gradient zone and the inflection point of the gradient zone of gravity variation, which is basically consistent with the strike of the Kangxiwa fault on the western boundary of the Bayan Hara block; the 2010 Yushu M s7.1 earthquake occurred on the Ganzi-Yushu fault along the high gradient zone of gravity change and the southern boundary of the Bayan Hara block; and the Jiuzhaigou M s7.0 earthquake in 2017 occurred at the intersection of the Tazang fault and the Minjiang fault in the high-gradient zone of gravity change and the northeastern boundary of the Bayan Hara block. (4) Gravity data reliably reflect the 7 earthquakes with magnitude 7 or above that have occurred in the Qinghai-Tibet Plateau since 2001. Obvious regional gravity anomalies and high-gradient zones were observed in the epicenter area and its vicinity prior to the earthquakes, which may be the gravity precursor information observed during the process of earthquake preparation. The authors made medium-term forecasts before the Yutian M s7.3 earthquake in 2008, the Wenchuan M s8.0 earthquake in 2008, the Lushan M s7.0 earthquake in 2013, the Yutian M s7.3 earthquake in 2014, and the Jiuzhaigou M s7.0 earthquake in 2017, primarily focusing on earthquake location based on gravity anomaly variations.

Postglacial gravity change in Fennoscandia—three decades of repeated absolute gravity observations

Postglacial gravity change in Fennoscandia—three decades of repeated absolute gravity observations

Using GPS and absolute gravity observations to separate the effects of present-day and Pleistocene ice-mass changes in South East Greenland

Measurements of vertical crustal uplift from bedrock sites around the edge of the Greenland ice sheet (GrIS) can be used to constrain present day mass loss. Interpreting any observed crustal displacement around the GrIS in terms of present day changes in ice is complicated, however, by the glacial isostatic adjustment (GIA) signal. With GPS observations alone, it is impossible to separate the uplift driven by present day mass changes from that due to ice mass changes in the past. Wahr et al. (1995) demonstrated that viscoelastic surface displacements were related to the viscoelastic gravity changes through a proportionality constant that is nearly independent of the choice of Earth viscosity or ice history model. Thus, by making measurements of both gravity and surface motion at a bedrock site, the viscoelastic effects could be removed from the observations and we would be able to constrain present day ice mass changes. Alternatively, we could use the same observations of surface displacements and gravity to determine the GIA signal. In this paper, we extend the theory of Wahr et al. (1995) by introducing a constant, Z, that represents the ratio between the elastic changes in gravity and elastic uplift at a particular site due to present day mass changes. Further, we combine 20 yrs of GPS observations of uplift with eight absolute gravity observations over the same period to determine the GIA signal near Kulusuk, a site on the southeastern side of the GrIS, to experimentally demonstrate the theory. We estimate that the GIA signal in the region is 4.49±1.44mm/yr and is inconsistent with most previously reported model predictions that demonstrate that the GIA signal here is negative. However, as there is very little in situ data to constrain the GIA rate in this part of Greenland, the Earth model or the ice history reconstructions could be inaccurate (Khan et al., 2016). Improving the estimate of GIA in this region of Greenland will allow us to better determine the present day changes in ice mass in the region, e.g. from GRACE.

Absolute gravity observations in Norway (1993–2014) for glacial isostatic adjustment studies: The influence of gravitational loading effects on secular gravity trends

We have compiled and analyzed FG5 absolute gravity observations between 1993 and 2014 at 21 gravity sites in Norway, and explore to what extent these observations are applicable for glacial isostatic adjustment (GIA) studies. Where available, raw gravity observations are consistently reprocessed. Furthermore, refined gravitational corrections due to ocean tide loading and non-tidal ocean loading, as well as atmospheric and global hydrological mass variations are computed. Secular gravity trends are computed using both standard and refined corrections and subsequently compared with modeled gravity rates based on a GIA model. We find that the refined gravitational corrections mainly improve rates where GIA, according to model results, is not the dominating signal. Consequently, these rates may still be considered unreliable for constraining GIA models, which we trace to continued lack of a correction for the effect of local hydrology, shortcomings in our refined modeling of gravitational effects, and scarcity of observations. Finally, a subset of standard and refined gravity rates mainly reflecting GIA is used to estimate ratios between gravity and height rates of change by ordinary and weighted linear regression. Relations based on both standard and refined gravity rates are within the uncertainty of a recent modeled result.

Observed secular gravity trend at Onsala station with the FG5 gravimeter from Hannover

Abstract Annual absolute gravity measurements with a FG5 instrument were performed in Onsala Space Observatory by the Institute of Geodesy of the Leibniz Universität Hannover from 2003 to 2011 and have been continued with the upgraded meter FG5X in 2014. Lantmäteriet, Gävle, with their FG5 absolute gravimeter have visited Onsala since 2007. Because small systematic errors may be inherent in each absolute gravimeter, their measuring level and a resulting bias (offset) between the instruments must be controlled over time by means of inter-comparison. From 2007 to 2014, 8 direct comparisons took place well distributed over the time span. A complete re-processing of the absolute gravity observations with the Hannover instrument has been conducted to improve the reduction of unwanted gravity effects. A new tidal model is based on continuous time series recorded with the GWR superconducting gravimeter at Onsala since 2009. The loading effect of the Kattegat is described with a varying sea bottom pressure (water and air mass load) and has been validated with the continuous gravity measurements. For the land uplift,which is a result of the still ongoing glacial isostatic adjustment in Fennoscandia, a secular gravity trend of −0.22 μGal/yr was obtained with a standard deviation of 0.17 μGal/yr. That indicates a slight uplift but is still not significantly different from zero.

A study on the Fennoscandian post-glacial rebound as observed by present-day uplift rates and gravity field model GOCO02S

Repeated absolute gravity measurements in Fennoscandia have revealed that the on-going post-glacial rebound can be regarded as a pure viscous flow of mantle mass of density 3390 kg/m3 towards the central part of the region caused by a gravity/uplift rate of −0.167 μGal/mm. Our model estimates the rebound induced rates of changes of surface gravity and geoid height to have peaks of −1.9 μGal/yr and 1.6 mm/yr, respectively, the former being consistent with absolute gravity observations. The correlation coefficient of the spherical harmonic representations of the geoid height and uplift rate for the spectral windows between degrees 10 and 70 is estimated to −0.99±0.006, and the maximum remaining land uplift is estimated to the order of 80 m. Both the (almost) linear increase of relaxation time with degree and the linear relation between geoid height and uplift rate support a model with mass flow in the major part of the mantle and disqualify the model with a flow in a thin channel below the crust. The mean viscosity of the flow in the central uplift region is estimated to 4×1021 Pa s.

Modeling of Atmospheric Gravity Effects for High-Precision Observations

Temporal variations of atmospheric density distribution induce changes in the gravitational air mass attraction at a specific observation site. Additionally, the load of the atmospheric masses deforms the Earth’s crust and the sea surface. Variations in the local gravity acceleration and atmospheric pressure are known to be corrected with an admittance of about 3 nm/s2 per hPa as a standard factor, which is in accordance with the IAG Resolution No. 9, 1983. A more accurate admittance factor for a gravity station is varying with time and depends on the total global mass distribution within the atmosphere. The Institut für Erdmessung (IfE) performed absolute gravity observations in the Fennoscandian land uplift area nearly every year from 2003 to 2008. The objective is to ensure a reduction with 3 nm/s2 accuracy. Therefore, atmospheric gravity changes are modeled using globally distributed ECMWF data. The attraction effect from the local zone around the gravity station is calculated with ECMWF 3D weather data describing different pressure levels up to a height of 50 km. To model the regional and global attraction, and all deformation components the Green’s functions method and surface ECMWF 2D weather data are used. For the annually performed absolute gravimetry determinations, this approach improved the reductions by 8 nm/s2 (-19 nm/s2 to +4 nm/s2). The gravity modeling was verified using superconducting gravimeter data at station Membach inBelgiumimproving the residuals by about 15%.

Gravity changes before and after the 2010 Ms7.1 Yushu earthquake

Absolute and relative gravity observations from 1998–2010 from the China Crustal Movement Observation Network, a major national scientific project, have been used to model the gravity field and its variations associated with the April 14, 2010 Ms7 . 1 Yushu earthquake. The evolution of the regional gravity field and its relationship with seismicity before and after the Yushu earthquake are studied. The observed gravity changes are closely related to the active Ganzi-Yushu Fault, and gravity measurements can be used to observe the migration of material accompanying active faults and crustal tectonics. The dynamic variation of the gravity field reflects its evolution prior to and during the Yushu earthquake. The gravity measurements near its epicenter are as large as 80 × 10 − 8 m/s 2 , and they show wave-like increases with time prior to the Yushu earthquake.