Gravity acceleration changes in Russian stations of comparing absolute gravimeters

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.

Application of deformation–induced topographic effect in interpretation of 2013–2016 spatiotemporal gravity changes at Laguna del Maule (Chile)

<p>The accurate deformation-induced topographic effect (DITE) should be used to account for the gravitational effect of surface deformation when analyzing residual spatiotemporal (time-lapse) gravity changes in volcano gravimetric or 4D micro-gravimetric studies, in general. Numerical realization of DITE requires the deformation field available in grid form. We compute the accurate DITE correction for gravity changes observed at the Laguna del Maule volcanic field in Chile over three nearly annual periods spanning 2013–2016 and compare it numerically with the previously used free-air effect (FAE) correction. We assess the impact of replacing the FAE by DITE on the model source parameters of analytic inversion solutions and apply a new inversion approach based on model exploration and growing source bodies. The new inversion results based on the DITE correction shift the position of the mass intrusion upwards by a few hundred meters and lower the total mass of the migrated fluids to roughly a half, compared to the inversion results based on the local-FAE correction. Our new Growth inversion results indicate that vertical dip-slip faults beneath the lake, as well as the Troncoso fault play active roles in hosting migrating liquid. We also show that for the study period, the DITE at Laguna del Maule can be accurately evaluated by the planar Bouguer approximation, which only requires the availability of elevation changes at gravity network benchmarks. We hypothesize that this finding may be generalized to all volcanic areas with flatter or less rugged terrain and may alter interpretations based on the commonly used FAE corrections.</p>

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

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.

Потенциальные возможности энергосбережения при эксплуатации системы водоотведения крупного города

В статье, без математической формализации, опираясь только на физические представления о процессе водоотведения крупного города, вскрывается потенциал экономии электроэнергии при транспортировке сточных вод по разветвленной напорно-самотечной сети. Этот потенциал, заключенный в самой ее структуре, может быть реализован путем целенаправленного оперативного перераспределения потоков сточных вод по канализационным насосным станциям и транспортным магистралям сети, добиваясь минимума суммарных затрат электроэнергии всеми насосными станциями. Показано, что расчет такого перераспределения возможен только на базе математической модели объекта, формулируя и решая соответствующую оптимизационную задачу. Обсуждаются требования, которым должна удовлетворять математическая модель объекта, и показываются ее возможности при управлении сетью не только в нормальных эксплуатационных режимах, но и при аварийных ситуациях. Рассмотрение проблемы базируется на положительных результатах широкомасштабного производственного эксперимента, проведенного ранее, по оптимальному управлению участком системы водоотведения Москвы.The article, without mathematical formalization, with due consideration of physical interpretations of the process of wastewater disposal in a large city, reveals the potential for energy savings in the process of wastewater transportation in an extensive gravity network, enclosed in its very structure. This potential can be fulfilled through targeted operational redistribution of wastewater flows over sewage pumping stations and transportation mains of the network, achieving the minimum of total energy consumption by all pumping stations. It is shown that the calculation of such a redistribution is possible only on the basis of a mathematical model of the project by formulating and solving the corresponding optimization problem. The requirements that the mathematical model of the project shall meet are discussed and its capabilities are shown while operating the network not only in normal operating conditions but also in emergency situations. The consideration of the problem is based on the positive results of a large-scale industrial experiment conducted earlier on the optimal management of a section of the Moscow sanitation system.

Refined prediction of vertical gradient of gravity at Etna volcano gravity network (Italy)

Predicted values of the vertical gradient of gravity (VGG) on benchmarks of Etna’s monitoring system, based on calculation of the topographic contribution to the theoretical free-air gradient, are compared with VGG values observed in situ. The verification campaign indicated that improvements are required when predicting the VGGs at such networks. Our work identified the following factors to be resolved: (a) accuracy of the benchmark position; (b) gravitational effect of buildings and roadside walls adjacent to benchmarks; (c) accuracy of the digital elevation model (DEM) in the proximity of benchmarks. Benchmark positions were refined using precise geodetic methods. The gravitational effects of the benchmark-adjacent walls and buildings were modeled and accounted for in the prediction. New high-resolution DEMs were produced in the innermost zone at some benchmarks based on drone-flown photogrammetry to improve the VGG prediction at those benchmarks. The three described refinements in the VGG prediction improved the match between predicted and in situ observed VGGs at the network considerably. The standard deviation of differences between the measured and predicted VGG values decreased from 36 to 13 μGal/m.