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Ten years ago a systematic survey of gravity tidal effects started in the Pannonian basin. In the framework of an international cooperation between Austria and Hungary 1-3 year long time series were recorded at 5 (mostly permanent seismological) stations with an LCR G meter (G949) having no feed-back system. It was improved by an electro-optical readout system for continuous recording at 1 Hz and equipped by an autonomous leveling platform keeping the instrument in nearly horizontal position and an electromotor driven micrometer dial to compensate long term instrumental drift remotely. The reference station was the Conrad Observatory (COBS), Austria where this system has been run co-located with GWR SG025 (operated by Zentralanstalt für Meteorology und Geodynamik, Wien) both at the beginning and at the end of the project. The largest distance was about 600 km in E-W direction between COBS and TRPA (Tarpa, Hungary) stations. The recorded time series were corrected for standard (e.g. barometric) and non-standard (e.g. uncompensated instrumental long-level tilt) effects and analyzed by the ETERNA package. The results show small (< 1%) but clear systematic increase of the variation of ratio O1/M2 tidal constituents (uncorrected for loading effects) from west to east. It is in good accordance with the theory and its measure was compared to synthetically calculated variations provided by different ocean loading models., The 28th IUGG General Assembly (IUGG2023) (Berlin 2023)

The Classical Karst is a limestone plateau stretching between Italy and Slovenia over an area of about 600km2.The aquifer of Classical Karst contains a complex network of conduits, shafts and large voids that are fed by theautogenic recharge and allogenic input of the Reka River. The Reka River sinks underground in the Škocjan Cavesand continues its underground flow for almost 40km until it reaches the Adriatic Sea at the Timavo Springs. Theriver shows high discharge variations; with minimal discharge below 0.3 m3/s and maximal discharge reachingover 350 m3/s. As the conduit system cannot efficiently drain large discharge, huge water masses are stored inthe epiphreatic voids of the aquifer during flood events. Škocjan Caves present such storage, where a vast amountof water is temporary stored during intense rain. Further evidences of the impressive water movements in thissystem could be found in the geodetic time-series recorded by the Grotta Gigante horizontal pendulums, whichshow deformation transients during Reka flood events. Gravimetry could be a useful tool to obtain local mass balances of such complex system, contributing together withthe other classical hydrologic prospections in depicting the water dynamics in this karstic environment. In additionto this gravimetry represents the ideal completion to the already set up geodetic instrumentation in the ClassicalKarst region. In the last year, we installed two continuous recording gravity stations, near the Škocjan caves and inside the GrottaGigante cave. The Škocjan caves serve as a test site because the cave geometry and the hydraulic system here arewell known. The Grotta Gigante site offers a quiet place and long term geodetic time-series but on the other hand,the hydrodynamics here are less clear. In this contribution, we present the simulations in support to the placement of the instruments and the first analysisconducted on the observed gravity time-series. For the Škocjan caves our simulations estimate that this mass accu-mulation could generate gravity signals up to 30 microGal for extreme events with peak discharge over 250m3/slasting for 1-1.5 days, accumulating over 35 106m3of water. The recorded data in Škocjan supports our simula-tions: a prominent peak up to 5 microGal of amplitude was recorded during a 14 106m3flood event on October2018. We believe that the Classical Karst represents an interesting study case for both the geodetic and hydrologic com-munities; the Škocjan cave offers a natural laboratory to optimally assess the contribution of gravimetry as a toolfor monitoring underground fluid mass movements.

In this contribution, activities of the AlpArray Gravity Research Group (AAGRG) are introduced. Since 2018, this group in the frame of the AlpArray project (http://www.alparray.ethz.ch/en/home/) prepares gravity and other data sets to support multidisciplinary goals of the project. It is focused on the mantle, plate and surface processes in the Alps-Apennines-Carpathians-Dinarides orogenic system. In 2018, the AAGRG set up its own methodology guidelines and assembled available land-gravity data and digital elevation model (DEM) data from all the participating countries. Our presentation targets especially three goals: 1) to introduce AAGRG activities as an integral part of the AlpArray project for studying Alpine orogeny – a goal that by definition requires international cooperation, 2) to review the input data and the works accomplished so far, and, 3) to discuss the steps to be taken to produce detailed gravity maps of the region – the first Alps-dedicated gravity field data set. We plan to prepare gravity grids in a homogeneous processing approach of either 2x2 km or 4x4 km resolution, depending on the coverage and data quality. The final data sets will be made public in late 2019. A special emphasis is put on the calculation of the Bouguer anomaly using ellipsoidal rather tha normal heights. For calculating topographic effects the preference is given to local DEMs, where available, as they often provide higher quality and spatial resolutions. The public gravity data sets are evaluated with the high-resolution geopotential models like EIGEN-6C4 or EGM2008 – a useful means for identifying biases in the data coming from various countries and campaigns.

A pan-Alpine gravity data map, homogeneous regarding input data sets, applied methods and corrections as well ascommon reference frames, is not available yet. Therefore, all countries around the Alps have agreed to contributewith gravity data and/or gravity data processing techniques to a recompilation of the alpine gravity field in theframe of the AlpArray Gravity Research Group (AAGRG). Also to collaborate with other groups in AlpArray.In the last year group members met two times to set up guidelines for joint processing and homogenizationof existing gravity data sets. Following the results and appointments of the last technical AAGRG meeting inBratislava October 2018, the members of the 9 participating countries decided to present a first data set of theBouguer gravity field in September 2019 on a 2km x 2km or 4km x 4km grid for the public. Other compilationswill follow: maps of Free Air Gravity, regional field and the corresponding residual gravity field. These new datasets will be available to all AlpArray partners for interdisciplinary work and modelling.This new Bouguer anomaly will be station completed with at least 1 point/4 km2 resolution and compiledaccording to the most modern criteria. In general, even though global models like SRTM1 perform well, thepreference was given to local DEMs - if available. Two software packages for topographic corrections on thebase of ellipsoidal heights are available: “TOPOSK”, developed by Slovak colleagues, and the “adaptive masscorrection” from the Kiel group. The results of both methods are being tested and compared. The geophysicalindirect effect and its determination are also taken into account. Special emphasis is put on the lakes in the studyarea. They have a considerable effect on the gravity of stations that lie at their edges (for example, the partiallyvery deep reservoirs in the Alps). In the Ligurian and the Adriatic seas ship data of the Bureau GravimétriqueIinternational will be used. Although not unproblematic, these data got the preference over satellite data.In the AAGRG, long discussions were centered on the calculation of long-distance effects of topogra-phy/bathymetry and its compensating masses (root). The first compilation of the AA Bouguer anomaly mapwill, however, be prepared WITHOUT taking long-distance effects in account. The group agreed to extendthe correction radius to the Hayford zone O2(167 km). All topographic corrections will be calculated as masscorrections between the physical surface and the ellipsoidal reference. The group further discussed the necessityof a 3D interpolation of the gravity grid values. Although a 3D interpolation would be required from themethodological-theoretical point of view (the problem is the non-identical gravity and height grids), it was decidedto perform a 2D interpolation in the first compilation - the method of Kriging shall be applied. The poster will visualize the mentioned correction effects and illuminate the necessity of a complete revision of the existing land based Alpine gravity data.

This volume aims at conveying the rich and interdisciplinary topics discussed at the 18th Geodynamics and Earth Tides Symposium, Trieste, 2016. For seventeen times the gathering was named the Earth Tides Symposium, when giving tribute to the evolution of the observed signals, the term geodynamics was added to the title.The present volume aims at a full coverage of the Symposium by including the entire list of abstracts that were presented either as oral or poster presentations

AlpArray Gravity Research Group (AAGRG) compiles a homogeneous gravity data set across the Alpine area, creates related gravity products and uses them for studies from small to regional to continental scales, as well as for joint inversion with other datasets.

The International Geodynamics and Earth Tide Service (IGETS) was established in 2015 by the International Association of Geodesy (IAG). IGETS continues the activities of the Global Geodynamics Project (GGP, 1997-2015) to provide support to geodetic and geophysical research activities using superconducting gravimeter data within the context of an international network. The primary objective of IGETS is to provide a service to monitor temporal variations of the Earth’s gravity field through long-term records from ground gravimeters, tiltmeters, strainmeters and other geodynamic sensors. IGETS also continues the activities of the International Center for Earth Tides, in particular, in collecting, archiving and distributing Earth tide records from long series of the various geodynamic sensors. This report is a compilation of data descriptions originating to a large part from GGP but including updates and extensions for IGETS.

International audience; The Vienna Basin at the transition between the Alpine and Carpathian belt hosts a number of large Pleistocene sub-basins forming along an active continental scale strike-slip fault (Vienna Basin strike-slip fault). We utilize first-order derivatives from industrial Bouguer gravity data to unravel the impacts of Pleistocene kinematics on the Vienna Basin and to compensate for the lack of near-surface fault data. Anomalies have been evaluated by independent geophysical and geological data and were integrated to build up a tectonic model. Factors influencing the wavelength and the amplitude of anomalies were additionally investigated by 2-D models to better interpret field data. Subsidence and related accumulation of Quaternary sediments in the Vienna Basin produce significant gravity signals related to the activity of the strike-slip fault. The constrained fault patterns and structures highlight tight and elongated transtensional pull-apart basins with typically associated features like separated depocenters and Riedel fractured sidewalls in an en-echelon alignment. Further Pleistocene basins are highlighted as tectonic grabens developing along branches of the master fault. The Vienna Basin is additionally affected by minor deformation represented by both subsidence along major Miocene sidewalls and NW-SE faulting resulting in distinct topographic features, which manifests kinematics on a regional scale. The clear density contrasts between Miocene marine and Quaternary terrestrial sediments, as well as the exceptional database, provide a unique framework to demonstrate advantages of incorporating gravity derivatives for near-surface fault analysis.