86,596 research outputs found
Comparing and combining space and terrestrial techniques in northeastern Italy to determinate station motions
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Crustal movements in northeastern Italy from permanent GPS stations
No full textThe horizontal absolute motion vectors of northeastern Italy, obtained from the GPS data of a permanent network are compared to the NUVEL1A NNR plate motion model. The results indicate that these sites are moving faster than predicted by the model and with azimuths slightly more northward oriented. The directions of absolute motion in the no-net-rotation system confirm the motion of the Adriatic plate in the global circuit where Africa, Europe and the intervening Adriatic plate are moving north-eastward, although at different velocities and with small variable azimuths which determine relative plate interactions. The data suggest shortening of a few mm/yr between Trieste, located at the leading edge of the Dinarides orogen and the Emilia-Romagna Marina di Ravenna, Medicina and Bologna sites positioned above the Apennines accretionary prism. This can be interpreted either as active thrusting of the Dinarides or/and active thrusting in the Apennines accretionary prism. Seismic reflection profiles and seismicity indicate that both orogens are active, but the Dinarides appear to have slower convergence rates. Active thrusting supports the notion of a lively and retreating subduction beneath the northern Apennines. The height time data of the same sites show subsidence rates of different magnitude. The rates of Marina di Ravenna and Bologna are, to a large extent, of anthropogenic nature
A combined GPS and Gravity analysis to study the effect of environmental parameters
No full textGeodetic in-situ observations are always effected by environmental parameters like atmosphere, ocean and hydrology. It is often criticised that seasonal effects accounted for global network analysis do not significantly improve the resulting parameters. In a local case study at Medicina, space geodetic (GPS and VLBI) and gravity observations (SCG and FG5) are used together with environmental observations and models to provide significant information both on the seasonal fluctuation as well as on the linear and non-linear long-term trend in height. Models of seasonal height and gravity components have been achieved by accounting for loading and mass effects, by atmosphere, non tidal ocean and the local hydrology. This last component shows to be a major contribution of the seasonal variations not only in terms of loading and mass variations but also for soil consolidation effects induced by water table decrease / increase on the clayey soil in Medicina. The local hydrology is an important component to understand the seasonal effects but it is difficult and / or expensive to get sufficient information at the observation sites. It will be demonstrated that regional and global information on hydrology, the Hydrological Balance and GRACE results used as input can satisfactory replace locally observed environmental data. The experiment carried out in Medicina demonstrates that only the combined reduction of the effect of environmental parameters will improve the overall analysis. Rigorously applied it allows to study linear and non-linear long-term station variations. There is a high probability that the consequent consideration of environmental parameters will have positiv effects on the long-term evolution of the global reference frame
Observing and assessing seasonal non-tidal ocean loading through ocean, continuous GPS and gravity data in the Adriatic area
No full textComparing and combining space and terrestral geodetic techniques to monitor crustal deformation
No full textIt is of particular importance to define and establish appropriate observational strategies characterized by the ability to measure, with high accuracy, spatially and time continuous deformations of the land surface. An ensemble of space, airborne and terrestrial techniques can be adopted by taking advantage of the complementary strengths of the different observations. We present a network encompassing northeastern Italy, which extends from the Apennines to the southeastern Po Plain and, along the Adriatic coast, to the Venice area and Trieste. First results mainly concern a study of land subsidence performed by comparing and combining different space and terrestrial techniques, which were co-located in several stations of the network. High-accuracy knowledge of subsidence rates is of particular importance in the Venice area for the re-organization of the lagoon territory and for building an adequate protection from increasing sea level and extreme events. Examples are provided for the stations in the network such as Medicina, Bologna and Marina di Ravenna where the available data series are several years long. At Medicina, the results of CGPS, superconducting and absolute gravimeter and InSAR observations, in combination with several meteoclimatic data series, are compared and combined. At the Bologna station, CGPS, absolute gravity and InSAR data are acquired while at Marina di Ravenna, on the Adriatic coast, CGPS and InSAR observations are available. All InSAR data are processed by means of the PS technique, thus obtaining a dense grid of measures over the study area. The ensemble of adopted space and terrestrial techniques will make it possible to acquire a thorough understanding of seasonal, long-term regional/local geophysical phenomena as well as climate-related impacts affecting the station motions
Height seasonal oscillations and long-term trends from a combination of GPS, gravity and InSAR data
No full textA fundamental development of the next coming years shall be the definition and the implementation of a high-accuracy and space-time continuous observation system for monitoring Earth’s surface deformation. The IAG project GGOS (Global Geodetic Observing System) will be the geodetic contribution to such a realization. A detailed knowledge of the crustal deformation is a key element to achieve a thorough comprehension of how the solid Earth responds to deformational forces and for an improved understanding of the seismogenetic cycle. We have studied and applied a combined observational strategy for monitoring and reliably identifying both seasonal and log-term crustal movements, namely height variations/changes. The strategy adopted is based on a multidisciplinary approach that combines the information provided by GPS, InSAR and terrestrial gravimetry. The results of these different techniques are compared and combined in a study on land subsidence in the southeastern Po Plain and the northern Adriatic coast, in Italy
Comparing and combining space and terrestrial techniques in northeastern Italy to determinate land subsidence
No full textObserving and assessing non-tidal ocean loading using ocean, continuous GPS and gravity data in the Adriatic area
No full textThe effect of nontidal ocean loading (NTOL) is
observed in the height series of four permanent GPS
stations in the northern Adriatic. A validation of the
ECCO model is performed by comparing model estimates
of sea-level anomalies from tide-gauges with TOPEX/
POSEIDON data, and ECCO model estimates of bottom
pressure with those derived from temperature and salinity
observations. The amplitudes of theECCO sea-level anomaly
are found to be 1.4 times smaller than observations; bottom
pressure is 2 times smaller. Using a Green’s functions
approach to determine elastic deformations, the ECCO ocean
bottom pressure is used to estimate surface displacements at
the GPS sites. Model results were compared with the height
series and with the observed NTOL effect. The height series
and the predicted NTOL are highly correlated at all four
stations. The analysis performed on superconducting
gravimeter data at the Medicina station also shows high
correlation
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