Measurement of absolute gravity acceleration in Firenze

Abstract. This paper reports the results from the accurate measurement of the acceleration of gravity g taken at two separate premises in the Polo Scientifico of the University of Firenze (Italy). In these laboratories, two separate experiments aiming at measuring the Newtonian constant and testing the Newtonian law at short distances are in progress. Both experiments require an independent knowledge on the local value of g. The only available datum, pertaining to the italian zero-order gravity network, was taken more than 20 years ago at a distance of more than 60 km from the study site. Gravity measurements were conducted using an FG5 absolute gravimeter, and accompanied by seismic recordings for evaluating the noise condition at the site. The absolute accelerations of gravity at the two laboratories are (980 492 160.6 ± 4.0) μGal and (980 492 048.3 ± 3.0) μGal for the European Laboratory for Non-Linear Spectroscopy (LENS) and Dipartimento di Fisica e Astronomia, respectively. Other than for the two referenced experiments, the data here presented will serve as a benchmark for any future study requiring an accurate knowledge of the absolute value of the acceleration of gravity in the study region.

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Repeated absolute gravity measurements on a dense network at Campi Flegrei – a reliable tool for volcano monitoring

Advances in Geosciences ◽

10.5194/adgeo-52-41-2020 ◽

2020 ◽

Vol 52 ◽

pp. 41-54

Author(s):

Giovanna Berrino ◽

Giuseppe Ricciardi

Keyword(s):

Hydrothermal System ◽

Field Measurements ◽

Volcano Monitoring ◽

Campi Flegrei ◽

Absolute Gravity ◽

Absolute Gravimeter ◽

Time Intervals ◽

Gravity Measurements ◽

Gravity Network ◽

Absolute Measurements

Abstract. Since 1981, relative gravity measurements have routinely carried out at the Campi Flegrei caldera, a densely populated area. The gravity network also includes two absolute stations periodically measured with a laboratory absolute gravimeter, which does not permit field measurements. At the end of 2014, the Osservatorio Vesuviano, Section of Napoli of the Istituto Nazionale di Geofisica e Vulcanologia (INGV-OV), acquired a portable absolute gravimeter that allows field operations on outdoor sites. Therefore, in 2015 a dense absolute gravity network was established in Campi Flegrei. This will permit an advanced approach for volcano monitoring. The net consists of 36 stations, 34 of which located inside the caldera and placed upon or very close to gravity stations belonging to the relative network. Five surveys were carried out on June 2015, on February and November 2017, on October 2018 and on October 2019. The comparison with height changes suggests that significant Δg are partly due to the uplift occurred over the same time intervals and mostly to shallow processes associated to the dynamic of the local hydrothermal system. The comparison with the gradients observed during the last large uplift (1982–1984) and the following subsidence (1985–2003) confirms this observation. These results suggest that the present activity may be due to a transient or pulsating phenomenon as the alternating recharge/discharge of fluids in the surface hydrothermal system. Gravity changes detected by absolute measurements are in good agreement with those obtained by relative ones, and confirms the feasibility of this methodology for volcano monitoring. Finally, they also encourage replacing the relative networks with absolute ones, with all the consequent advantages.

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Gravity changes before and after the 2015 Mw7.8 Nepal earthquake

10.5194/egusphere-egu2020-4304 ◽

2020 ◽

Author(s):

Weimin Xu ◽

Shi Chen ◽

Hongyan Lu

Keyword(s):

Source Region ◽

Absolute Gravity ◽

Nepal Earthquake ◽

Source Regions ◽

Gravity Changes ◽

Seismogenic Source ◽

Before And After ◽

Gravity Measurements ◽

The Absolute ◽

Regional Gravity

Based on the absolute gravity measurements of 4 gravimetric stations (Shigatse, Zhongba, Lhasa and Naqu) in southern Tibet surveyed from 2010 to 2013, we modeled the source region as a disk of 580 km in diameter by Hypocentroid model, shown that the gravity increase at these stations may be related to mass changes in the source region of the 2015 Mw7.8 Nepal earthquake. We analyzed the characteristics of gravity variations from the repeated regional gravity network, which including the 4 absolute gravimetric stations and 13 relative gravimetric stations from 2010 to 2019, to study the characteristics of gravity changes before and after the earthquake.We firstly estimated the reliability of the absolute gravity measurements by the errors of each station, and considered the effect of vertical displacement, denudation of surface mass, GIA correction and the secular and background gravity changes. Secondly we employed the Bayesian adjustment method for the relative gravimetric network data analysis, which was more robust and adaptive for solving problems caused by irregular nonlinear drift of different gravimeters, and then carried out error analysis for the repeated relative gravity measurements. Furthermore, we took the Shigatse station as example, which covered absolute and relative measurements and was most close to the Hypocenter of the inversion Hypocentroid model, the hydrologic effects of the Shigatse station was modeled exactly, and the results shown that the secular and background gravity changes were much smaller than the observed gravity changes. Lastly we studied the characteristics of gravity changes before and after the earthquake through the Hypocentroid model, we found the coincident gravity increase both in absolute and repeated regional gravity results before the earthquake, and gravity decreased after the earthquake, which suggested that the pre-earthquake gravity increase may be caused by strain and mass (fluid) transfer in broad seismogenic source regions of the earthquake. Moreover, the study indicated that high-precision ground gravity measurements (absolute and relative) may provide a useful method for monitoring mass changes in the source regions of potential large earthquakes.&#160;Acknowledgment: This research is supported by National Key R&D Program of China (Grant No.2018YFC1503806 and No.2017YFC1500503) and National Natural Science Foundation of China (Grant No.U1939205 and No.41774090).

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Gravity acceleration changes in Russian stations of comparing absolute gravimeters

Geodesy and Cartography ◽

10.22389/0016-7126-2021-977-11-8-15 ◽

2021 ◽

Vol 977 (11) ◽

pp. 8-15

Author(s):

V.D. Yushkin ◽

L.V. Zotov ◽

A.V. Basmanov ◽

R.A. Sermyagin

Keyword(s):

Gravitational Field ◽

Satellite Data ◽

Gravity Changes ◽

Grace Data ◽

Urgent Task ◽

The Absolute ◽

Gravity Network ◽

Gravity Acceleration

The article deals with the study of changes in the values of gravitational accelerations at the Russian comparison’s sites of the absolute gravimeters “Pulkovo”, “Svetloye” and “Zvenigorod” for the years of 2007–2013. A significant increase of the values instead of the expected decrease was obtained. The authors make an attempt to reveal the reasons for that basing on the calculation of the change in the gravitational field using the Bouguer and Faye corrections. The estimates do not fully explain the phenomenon, according neither to gravimeters nor to satellite data. At the sites of “Pulkovo” and “Svetloye”, the measured changes in the values differ from the calculated ones by +5,7 and 6,6 μGal, which significantly exceeds the errors of the absolute gravimeters. The change of the gravity varies from satellites GRACE data by 9,4 μGal at the “Zvenigorod” site. This may be due to local hydrological reasons. Determining the causes of gravity changes at the absolute stations of gravity network is an urgent task.

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Thirty years of precise gravity measurements at Mt. Vesuvius: an approach to detect underground mass movements

Annals of Geophysics ◽

10.4401/ag-6442 ◽

2013 ◽

Vol 56 (4) ◽

Author(s):

Giovanna Berrino ◽

Vincenzo d’Errico ◽

Giuseppe Ricciardi

Keyword(s):

Ground Deformation ◽

Reference Station ◽

Absolute Gravity ◽

Volcanic Area ◽

Gravity Station ◽

Gravity Changes ◽

Gravity Measurements ◽

Elevation Changes ◽

Gravity Network

Since 1982, high precision gravity measurements have been routinely carried out on Mt. Vesuvius. The gravity network consists of selected sites most of them coinciding with, or very close to, leveling benchmarks to remove the effect of the elevation changes from gravity variations. The reference station is located in Napoli, outside the volcanic area. Since 1986, absolute gravity measurements have been periodically made on a station on Mt. Vesuvius, close to a permanent gravity station established in 1987, and at the reference in Napoli. The results of the gravity measurements since 1982 are presented and discussed. Moderate gravity changes on short-time were generally observed. On long-term significant gravity changes occurred and the overall fields displayed well defined patterns. Several periods of evolution may be recognized. Gravity changes revealed by the relative surveys have been confirmed by repeated absolute measurements, which also confirmed the long-term stability of the reference site. The gravity changes over the recognized periods appear correlated with the seismic crises and with changes of the tidal parameters obtained by continuous measurements. The absence of significant ground deformation implies masses redistribution, essentially density changes without significant volume changes, such as fluids migration at the depth of the seismic foci, i.e. at a few kilometers. The fluid migration may occur through pre-existing geological structures, as also suggested by hydrological studies, and/or through new fractures generated by seismic activity. This interpretation is supported by the analyses of the spatial gravity changes overlapping the most significant and recent seismic crises.

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Hydrogeology correction in the gravitational field from satellite data

Geodesy and Cartography ◽

10.22389/0016-7126-2018-931-1-2-7 ◽

2018 ◽

Vol 931 (1) ◽

pp. 2-7

Author(s):

V.D. Jushkin ◽

L.V. Zotov ◽

O.A. Khrapenko

Keyword(s):

Gravitational Field ◽

Oil And Gas ◽

Repeated Measurements ◽

Geological Factors ◽

Grace Satellite ◽

Gas Pumping ◽

Acceleration Of Gravity ◽

Determination Of Parameters ◽

Gravity Acceleration

The results of repeated measurements of the acceleration of gravity by the Russian absolute ballistic field gravimeter GABL-M on points of oil and gas deposits in the permafrost over a five year period are presented. The changes of gravity acceleration by the absolute gravimeter and GRACE satellite were compared. The results of comparisons of differences gravity acceleration by ballistic gravimeter GABL-M and relative Canadian gravimeters CG5 were [i]shown. The errors in determination of parameters of the gravitational field ballistic gravimeter GABL-M and CG5 gravimeters group were presented. The method of measurement with the gravimeter GABL-M and the method of determining the vertical gradients relative CG5 gravity meters was described. The necessity of introducing corrections of hydrogeology is caused by influence of hydro geological factors on the gravitational field in the permafrost. They are comparable with the values of the field change in the result of gas pumping.

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

Journal of Geodesy ◽

10.1007/s00190-020-01470-9 ◽

2021 ◽

Vol 95 (2) ◽

Author(s):

Mirjam Bilker-Koivula ◽

Jaakko Mäkinen ◽

Hannu Ruotsalainen ◽

Jyri Näränen ◽

Timo Saari

Keyword(s):

Gravity Data ◽

Gravity Change ◽

Global Navigation Satellite Systems ◽

Absolute Gravity ◽

Data Sets ◽

Postglacial Rebound ◽

Land Uplift ◽

Satellite Systems ◽

Gravity Measurements ◽

Global Navigation Satellite

AbstractPostglacial 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.

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