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1

New challenges for the CEGRN

Caporali A.

Reports on Geodesy

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2011

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z. 2/91

9-18

EN

The Central European Geodynamic Reference Network is active since the early 1990's with a consistent and systematic activity of measurement, processing and scientific interpretation of the GPS and derived data. The project CERGOP 2 which was financed by the EU under FP5 has contributed to build the necessary cohesion and awareness of the different fields of expertise which are necessary to manage a geodetic network spanning Central Europe, and with important connections to other networks, in particular the EPN. In this second decade there are a number of challenges which will need a strong effort. The ambitious EPOS and TopoEurope projects are looking for a homogeneous and consistent dense velocity field for application to geodynamics and seismicity. The theme of the dense velocity field is present also within the IAG, in the working group 'Regional Dense Velocity Fields'. Finally, the way in which the ETRF2000 coordinates of stations in national networks evolve relatively to the stable part of Europe is related to the details of the 3D velocities. This is relevant to INSPIRE, and the obligation of the EU Countries to follow the ETR89 standards. CEGRN has the potential to effectively play an active role in these scientific issue, because the CEGRN campaigns are of high quality, fulfill state-of-the-art standards and extend over a very long lapse of time. Possible initiatives linked to the scientific projects mentioned above include 1) a participation in the proposed COST Action called TEGO 'Towards a European GNSS Observatory'; 2) a study of the best way to combine the CEGRN campaign solutions with the EPN network solution.

2

Geokinematics of Central Europe: new insights from CERGOP-2/Environment Project

Caporali A., Becker M., Fejes I., Gerhatova L., Ghitau D., Grenerczy G., Hefty J., Medac D., Milev G., Mojzes M., Mulic M.

Reports on Geodesy

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2007

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z. 2/83

7-46

EN

The CERGOP2 project funded by the European Union from 2003 to 2006 under the 5th Framework Programme benefits from repeated measurements of the coordinates of epoch and permanent GPS stations forming the CEGRN network in Central Europe, starting 1994. We report on the results of the systematic processing of the available data up to 2005. The analysis work has yielded the velocities of some 60 sites, covering a variety of Central European tectonic provinces, from the Adria indenter to the Tauern window, the Pannonian basin, the Vrancea Seismic Zone and the Carpathian Mountains. The estimated velocities define kinematical patterns which outline, with varying spatial resolution depending on the station density and history, the present day tectonic flow in Central Europe.The CEGRN data show that the majority of active contraction originating from the Eurasia Nubia plate boundary and the microplate between them is taken up primarily in the Eastern Alps, the Dinarides, and the Pannonian Basin. After removal from the ITRF2000 velocities of a rigid rotation accounting for the mean motion of stable Europe, the residual velocities have random orientations with 0.3 mm/yr scatter. This Iow figure provides an upper estimate for the level of rigidity of the European Platform. A 2.3 mm/yr north-south oriented convergence rate is implied by our data between Adria and the Southern Alps, and a narrow - -60 km wide- contraction zone in the Southern Alps is identified, consistently with earlier results. An eastward extrusion north of the contraction zone corresponds with the extension of the Tauern Window. In the southeastern boundary of the microplate, 4-4.5 mm/yr motion of Adria decreases to -1 mm/yr through the microplate, its boundary, and the Dinarides mountain range towards the southwestern part of the Pannonian Basin. Our data suggest that if the Pannonian Basin is subject to deformation, then it is most likely to be compressional than extensional. We conclude that compression and associated contraction due to the Adria collision with the Alps and the Dinarides is likely to fade away in the Western and Northern Carpathians, where our velocities and strain rates show no significant deformation.

3

Geokinematics of Central Europe from GPS data

Caporali A., Śledziński J.

Reports on Geodesy

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2006

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z. 2/77

17-28

EN

In several seismic or potentially seismic areas deformation processes at moderate depth generate deformation at the surface and measurement of such surface deformation is an important boundary condition to models of the evolution of interacting blocks before, during and after earthquakes. the network of some 160 permanent GPS stations disseminated in Europe under the European Permanent Network of EUREF and the CERGOP 2 Project of the European Union, with additional local densification stations, provides a valuable contribution to the estimate of the average surface strain rate. The expected strain rate is of the order of 20-40 nanostrian per year, corresponding to a velocity change of a few mm/year over distances of some hundreds of km. Consequently, we require accuracies in the velocities of fractions of mm/year and full control of systematic errors which may mask tectonic signals. Based on our systematic processing of GPS data from permanent European GPS stations covering nearly a decade (1995-2005) we present the large scale velocity flow across most of continental Europe and the associated horizontal gradient or strain rate field.

4

Final report presented by partner UNIPD for the period 01 April2003 - 31 July 2006

Caporali A., Facchinetti C., Bonafede L.

Reports on Geodesy

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2006

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z. 3/78

85-155

EN

Within the Project our group has been responsible of WP6, which addresses the stability of time series of coordinates of GPS stations used in the project. In addition we have supported WP1, WP4, WP7 and WP10.1, as scheduled. The time series we have analysed result from WP1 and WP5. We have combined normal equations from the EUREF network, and selected those stations which are relevant to the CERGOP 2 project. Likewise for Italian and Austrian stations we have stacked normal equations pertaining the national networks, and obtained time series which are useful to the science part of the Project. Finally we have addressed the normai equations of the CEGRN campaigns, up to the CEGRN 03 campaign, constructed time series and checked for their continuity. An in depth analysis of the time series was done for those sites which have been active with continuity for at least three years. We did this analysis for all the stations which met this requisite, including time series of a number of stations computed by the Austrian partner OLG. The analysis consisted in the identification, in the time and frequency domains of specific signatures, typically annual and semi annual, affecting the time series and can be of various origin, such as seasonal water flow or thermal dilatation of the antenna mount. After removal of the periodic signals, the power spectral density has been computed and the white and coloured components in the noise could be characterized. We report in most cases flicker phase noise at low frequencies and white noise at higher frequencies (>2 cycles/year), with a few exceptions in which the noise is white at all frequencies. A few stability problems are reported. In particular our own ASIA station was affected by mount instability in connection to a heavy snow storm in February 2006. This event was promptly noticed from the analysis and the mount problem could be solved. We have checked for local instabilities by looking at deviations of the estimated velocities from the expected pattern. We have verified that the stations contributing to the project have velocities agreeing with theoretical predictions. When this does not happen, then the station in most cases has a marginal tracking his tory, and we suspect that the discrepancies are attributable to a weak data set, more than true instability. The contribution to the Project includes, besides the data analysis part, two new permanent stations which were installed in Asiago and Rovigo as part of the Project, and regularly operated. Two doctoral stipendia have been awarded, and a Web page dedicated to our WP6 has been constructed, regularly maintained and linked to the Project's web page.

5

Final report presented by partner UNIPD for the period 01 april 2003 - 31 july 2006

Caporali A., Facchinetti C., Bonafede L.

Reports on Geodesy

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2006

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z. 4/79

399-417

EN

Within the Project our group has been responsible ofWP6, which addresses the stability of time series of coordinates of GPS stations used in the project. In addition we have supported WP1, WP4, WP7 and WP10.1, as scheduled. The time series we have analysed result from WP1 and WP5. We have combined normal equations from the EUREF network, and selected those stations which are relevant to the CERGOP 2 project. Likewise for Italian and Austrian stations we have stacked normal equations pertaining the national networks, and obtained time series which are useful to the science part of the Project. Finally we have addressed the normal equations of the CEGRN campaigns, up to the CEGRN 03 campaign, constructed time series and checked for their continuity. An in depth analysis of the time series was done for those sites which have been active with continuity for at least three years. We did this analysis for all the stations which met this requisite, including time series of a number of stations computed by the Austrian partner OLG. The analysis consisted in the identification, in the time and frequency domains of specific signatures, typically annual and semi annual, affecting the time series and can be of various origin, such as seasonal water flow or thermal dilatation of the antenna mount. After removal of the periodic signals, the power spectral density has been computed and the white and coloured components in tte noise could be characterized. We report in most cases flicker phase noise at low frequencies and white noise at higher frequencies (>2 cycles/year), with a few exceptions in which the noise is white at all frequencies. A few stability problems are reported. In particular our own ASIA station was affected by mount instability in connection to a snow storm in February 2006. This event was promptly noticed from the analysis and the mount problem could be solved. We have checked for local instabilities by at deviations of the estimated velocities from the expected pattern. We have verified that the stations contributing to the project have velocities agreeing with theoretical predictions. When this does not happen, then the station in most cases has a marginal tracking history, and we suspect that the discrepancies are attributable to a weak data set, more than true instability. Tie contribution to the Project includes, besides the data analysis part, two new permanent stations which were installed in Asiago and Rovigo as part of the Project, aad regularly operated. Two doctoral stipendia have been awarded, and a Web page to our WP6 has been constructed, regularly maintained and linked to the Projects web page.

6

MID term report presented by partner UNIPD for the period 01 April 2004 - 30 September 2004

Caporali A., Facchinetti C., Gallini G.

Reports on Geodesy

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2004

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nr 4/71

219--242

EN

Partner UNIPD is responsible for WP6 Time series analysis and provides support to a number of other related WP's. The output of WP6 is foreseen every third month, beginning month 6. At this stage (month 18) we report on the successful generation of time series for all the permanent stations for which we have the data available, that is the EPN stations plus a number of Austrian and Italian permanent stations which are not part of the EPN. Our analysis includes the statistical and spectral analyses of the time series, whenever it is meaningful, i.e. for time series longer than 3 years. The analysis is based on the processing of normal equation files. Each one of them is obtained from the combination of two normal equations for each week, and the multi year solution embodies constraints on the position and velocity datum which are considered as state of the art. According to this combination scheme, more normal equations can be combined, yielding a unified network. We have also developed the presentation and communication framework for our results, in the form of a web page. As soon as time series for other permanent stations in the study area are available, they can be processed accordingly. A number of activities have been done in the support to other WP's. More precisely we have supported WP1 as follows: o Raw data (RINEX) from the newly established stations ASIA and ROVI are sent regularly to the Project's Data Center in Graz; o Processed (NEQ/SNX) files from a network including permanent stations relevant to the Project have been sent to the Project's Data Center and to the responsible of WP5, to prepare the basis for the time series which will be the input to WP6.

7

Annual report presented by partner UNIPD for the period 01 April 2003 - 31 March 2004

Caporali A., Facchinetti C., Gallini G.

Reports on Geodesy

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2004

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nr 2/69

39--49

8

The contribution of the university of Padova to Central European Geodesy

Caporali A.

Reports on Geodesy

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2003

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z. 2/65

23-32

EN

The definition and maintenance of a geodetic reference system by modern techniques requires systematic temporal changes of the position of the defining stations to be taken in to account. Most of these drifts are accommodated by present day plate tectonics. If the lithospheric plate to which a given station belongs were perfectly rigid, then a simple plate model based upon rigid rotations about Eulerian poles would suffice to predict the horizontal coordinates of each station at any epoch, once the coordinates of that station are known at a reference epoch. In Europe, there are stations well located inside old, stable areas which may be considered rigid, but other stations are at or near continental margins undergoing active deformation, or are within a relatively recent portion of a tectonic unit subject to intraplate stress or volcanism. Velocities of stations in the most recent ITRF solutions do, in fact, exbibit in some cases departures from the NUVELIA NNR plate model in Europe and elsewhere, but the reasons for these discrepancies are not always well understood. For example, if a particular station of the network exbibits a velocity anomaly relative to a reference velocity model, then it is of interest to understand the reasons for the anomaly, and its spatial extent, that is if it is local to that station, or if nearby stations are also affected, and with which tapering as a function of distance. As part of the research activities in support of the CEI/CERGOP and EUREF, the time series of coordinates of European Permanent Network (EPN) stations in the Alpine - Mediterranean - Dinarides region are examined both in the time and space domains, and hypotheses are formulated on the reasons of systematic departures from linearity. The time domain analysis consists in the construction of the Power Spectra I Density and autocorrelation function of the time series of each coordinate for each station, the assessment of the type(s) of noise and periodicities, and an estimate of the uncertainty in the velocity. The space domain approach consists in cross correlating time series of stations and investigating the cross correlation function as a function of the space separation between pairs of stations. The combined analysis in the space and time domains of the time series provides a description of small but non negligible changes of coordinates the pernanent stations which should be taken into account if the realisation of the reference system is to be as accurate as the coordinates of the defining stations.

9

The contribution of the University of Padova to Central European Geodesy

Caporali A.

Reports on Geodesy

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2003

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z. 1/64

47-56

EN

The definition and maintenance of a geodetic reference system by modern techniques requires systematic temporal changes of the position of the defining stations to be taken into account. Most of these drifts are accommodated, by present day plate tectonics. If the lithospheric plate to which a given station belongs were perfectly rigid, then a simple plate model based upon rigid rotations about Eulerian poles would suffice to predict the horizontal coordinates of each station at any epoch, once the coordinates of that station are known at a reference epoch. In Europe, there are stations well located inside old, stable areas which may be considered rigid, but other stations are at or near continental margins undergoing active deformation, or are within a relatively recent portion of a tectonic unit subject to intraplate stress or volcanism. Velocities of stations in the most recent ITRF solutions do, in fact, exhibit in some cases departures from the NUVELIA NNR plate model in Europe and elsewhere, but the reasons for these discrepancies are not always well understood. For example, if a particular station of the network exhibits a velocity anomaly relative to a reference velocity model, then it is of interest to understand the reasons for , the anomaly, and its spatial extent, that is if it is local to that station, or if nearby stations are also affected, and with which tapering as a function of distance. As part of the research activities in support of the CEI/CERGOP and EUREF, the time series of coordinates of European Permanent Network (EPN) stations in the Alpine - Mediterranean - Dinarides region are examined both in the time and space domains, and hypotheses are formulated on the reasons of systematic departures from linearity. The time domain analysis consists in the construction of the Power Spectral Density and autocorrelation function of the time series of each coordinate for each station, the assessment of the type(s) of noise and periodicities, and an estimate of the uncertainty in the velocity. The space domain approach consists in cross correlating time series of stations and investigating the cross correlation function as a function of the space separation between pairs of stations. The combined analysis in the space and time domains of the time series provides a description of small but non negligible changes of coordinates the permanent stations which should be taken into account if the realization of the reference system is to be as accurate as the coordinates of the defining stations.

10

Progress report presented by partner UNIPD for the progress meeting of September 29-30, 2003, Warsaw

Caporali A.

Reports on Geodesy

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2003

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z. 3/66

59-62

11

Precise orbit determination using a LEO-GPS satellite to satellite tracking approach

Caporali A., Dalla Torre A., Facchinetti C.

Reports on Geodesy

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2003

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z. 2/65

221-233

EN

The tracking requirements for a Low Earth Orbit (LEO) satellite are defined by the overall accuracy of the results each mission is designed for. Examples of satellites asking for Precise Orbit Determination are remote sensing satellite and geodetic satellites. The paper addresses some basic considerations for the design of a GPS data processing technique for the high-precision position determination of a GPS/GLONASS receiver. Once the position of the receiver is known, this information can be used to determine the orbit of Low Earth Orbit (LEO) satellites. The precision requirements to be fulfilled have to be compatible with the definition of Precise Orbit Determination (POD): in most of applications the accuracy for post processed data is required to be meter or even sub decimetre in the radial direction, particularly in those cases where a radar altimeter is on board typically for oceanographic applications, or for Intefferometric SAR. The use of GNSS receiver on board and the support of a ground station network with a set of appropriate postprocessing tools allows to fulfil also the more stringent requirements for the Precise Orbit Determination. Two are the major class of teehniques that have been historically used: the Geometric and the Dynamic approaches. Each of these concepts had advantages and disadvantages. The most important advantage of the geometric approach relies on its simplicity and that it has the potential to work in the presence of forces which were absent from the dynamic model. Now that the IGS products have become fairly standardised, and very precise predictions are going to be available in the next future with a very short delay time, and space 'ali in view receivers' are capable of tracking all the visible satellites, and possibly also the GLONASS satellites, the geometric solution has to be reconsidered. The technique chosen to perform these solutions is then the simple geometric point positioning approaeh using, for every epoch, pseudoranges measurements smoothed using phase data. The navigation satellite orbits are taken from the International GPS Service (IGS) products. To test the GPS POD sensor, the data provided by some in-orbit satellites with on board GPS receivers (es: CHAMP and SAC-C) can be used.

12

Interferometric attitude and direction sensor using GPS carrier phase data

Caporali A., Dalla Torre A., Praticelli N.

Reports on Geodesy

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2003

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z. 2/65

173-193

EN

A prototype attitude sensor suitable for navigation on the Earth surface or for platforms in Low Earth Orbit has been implemented using pairs of GPS receivers. The attitude sensor provides two or three attitude angles depending on its configuration and provides aIso information on the deformation of the platform on which the GPS antenna are mounted. The basic measurement performed by the GPS Attitude Sensor consists in comparing the down-converted carrier phases from a pair of receivers. The fringe phase for each visible satellite is further differenced between satellites, to remove the drift of one receiver cIock relative to the other. The baseline joining a pair of antennas defines bodyfixed angles, which are estimated in real time using a two step procedure: a coarse estimation is first mad e with the Ambiguity Resolution Function (ARF) algorithm, and, second, the refined estimate is made by least squares. Assuming baselines ranging from 0.2 meters to 1 meter, the r.m.s. (root mean square) of the repeatability at 1 Hz varies from 1° to 0.25° for the horizontal angle (e.g. azimuth), and a factor of 2 larger for the vertical angle (e.g. elevation). For greater accuracy a longer baseline must be used, but it will be more difficult to select the correct integer ambiguities. To solve this problem compatibly with the requirement of real time processing, we use one intermediate antenna in a bootstrap mode: a 200 mm baseline is used to put for a first estimate of the solution; then the data from a 1000 mm baseline are used, in combination with the constraints coming from the 200 mm baseline, to obtain a refined solution. This approach yields a stable and accurate solution. AItematively, we have configured the three antennas at the corners of a triangle, to estimate the three body-fixed angles, the independent baseline lengths and of the angle in-between. The estimate is again made epoch-wise, i.e. regardless the value the parameters had at previous epochs. Alternatively, a limited memory filter can be used, to smooth the noise. The estimated angles are 'absolute' , that is geographicaIly unbiased, as they refer to the true geographic pole. The Software module allows the operator to communicate with the receivers through a serial interface to a PC, to perform and to display the orientation solution. The Software tool has been created in order to deal with receivers of different manufacturers and with different configurations. Considering the frame in which the GPS attitude sensor has been developed the following S/W environment was used: Borland Visual C++ selected to create the communication interface with the user to extract the raw data from the receivers and to display the results. Lahey FORTRAN90 selected to perform the attitude solution. The F90 module is mad e available to the C++ module as a Dynamically Link Library (DLL) and it's caIIed for each observation epoch. Complementary use of the GLONASS and GALILEO navigation sateIlites has the potential to improve epoch-wise on the geometry and, hence, on the r.m.s. Figure. A possible application for a long baseline configuration (e.g. 10 m) is to provide a reference for mapping the magnetic declination, for cartographic use. The sensor has the capability to measure relatively small (>0.005 m) changes in the baseline, simultaneously with the angles. As such, it can work as a strain gauge, e.g. to monitor large deformable structures in orbit or on the ground. If the angles are known in advance, like in the case of fixed GPS receivers on known coordinates, the sensor can be used for the determination of the variation of the distance between the antennas for long baselines (0.1-10km) in Real Time with high accuracy. A network of antennas spread in a large area can provide useful information for seismic studies. Having no moving parts, the sensor can withstand the shocks of the launch and is immune from thermal and mechanical drifts, but is sensitive to the occultation of the navigation sateIlites produced by nearby obstacles or structures.

13

State of strain in the Italian crust from geodetic data

Caporali A., Martin S., Massironi M., Baccini S.

Reports on Geodesy

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2001

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z. 3/58

121-138

EN

The area bounded by the Alpine chain to the North and Mediterranean/Ionian sea to the South is characterized by a wide range of tectonic phenomena, such as the identation of the Adria block into the Eastern Alp, lateral extrusion of the Tauern Window, unbending of the Adriatic lithosphere, opening of the Thyrrenian sea and subduction of the Ionian lithosphere beneath the Calabrian arc. This ongoing tectonics is accompanied by a relatively intense volcanism and seismicity, which justify the expectation of small but measurable horizontal and vertical displacements.

14

Contribution of the University of Padova to the EPN project on geokinematics

Caporali A., Baccini S.

Reports on Geodesy

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2001

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z. 3/58

101-120

EN

Time series of coordinates of permanent GPS stations are expected to exhibit a steady, linear trend in response to tectonic forces. This trend is, in fact, observed, but it is accompanied by variety of signatures, so that the overall spectral properties of the detrended, zero-mean time series differ from that of a random signal, especially in the medium (~~fraction of a year) to long (several years) period.The time series of the coordinates of 30 permanent GPS stations in the Alpine Mediterranean area with time spans from one to five years are presented.

15

Alpine network

Brockmann E., Calais E., Nocquet J., Caporali A., Vespe F., Weber G., Weber R., Stangl G.

Reports on Geodesy

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2001

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z. 3/58

91-100

16

Constraining the contemporary crustal deformation in Italy with geodetic data

Caporali A., Martin S., Massironi M.

Reports on Geodesy

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2000

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z. 8/54

179-193

EN

Using the EUREF 97 velocities as a velocity datum, we have computed velocities of additional, permanent GPS stations in Italy from week 995 to week 1060 (30 January 1999 to 6 May 2000), and the components of a two dimensional, horizontal strain rate tensor. When examined in the context of independent geological, seismological and geophysical knowledge, the map of the geodetically inferred strain rate field shows several interesting correlation with fault plane solutions and the geometry of preexisting faults. Our kinematic model features an extensional regime on theLigurian and Thyrrenean sea, along and West of the Apennines, up to the Adria shore, and compression in the Friuli region. In the Channel of Sicily, the relative motion of Lampedusa and Noto results in an extension, which fits the aseismic deformation pattern in the Pantelleria Rift system. The maximum deformations occur in the Central Apennines, with and extensional strain rate of 27 10(-9) yr(-1) and in the Southern Appenines, with and extensional strain rate of 23 10(-9) yr(-1). In areas characterized by intense fracturing, and superposition of fault system with different attitudes and trends, the GPS station are to sparce to account for the short wavelenght changes in stress regime. This lack of spatial resolution is evident in the Western Po Plain, or in the Messina strait, where the regime clearly changes on a shorter scale than the average distans beteen the GPS stations in those areas. With these exceptions , we conclude that the information coming from the geodetic strain rate data fits the broad scale neotectonic pattern inferred from several large scale faults, fault plane solutions of recent, shallow earthquakes, and other geophysical indicators of the stress regime.

17

The Italian network of permanent GPS stations

Caporali A.

Reports on Geodesy

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1999

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z. 3/44

165-168