APPLICATIONS OF SPACE GEODESY METHODS INROMANIA [304836]

APPLICATIONS OF SPACE GEODESY METHODS INROMANIA

Dr.Narvic Doru Mateciuc1, Dr.Andrei Bălă1

1[anonimizat]’s [anonimizat] a reflection of the complex geodynamic phenomena that occur in the crust and in the subcrustal lithosphere.[anonimizat] a [anonimizat], to the determination of the soil stability degree in inhabited areas or in those in which large industrial targets and utilities are intended to be placed in. The knowledge of movements affecting the Earth’s [anonimizat], [anonimizat] a topical issue. [anonimizat]. There are presented some of the most significant results achieved in the framework of each research project together with the limitations imposed by the used acquisition technology. [anonimizat] 1994, in a [anonimizat]'s involvement in a [anonimizat] a [anonimizat]461, also continued after 2003 with the continuous help of the University of Delft (Nederlands), a [anonimizat] a valuable support for the geodynamic studies. There are made brief references to the first application of the Finite Element Method in a GPS subnet from the Vrancea extended network together with some of the most important obtained results.[anonimizat] a [anonimizat], [anonimizat], to solve the very complex problem of the earthquake forecasting.

Keywords: [anonimizat],GPS, Earth’s crust.

INTRODUCTION

The most important objective of this paper is to discuss the main applications of geodetic measurements made by spatial geodesy techniques in Romania.

The applicability of GPS measurement has proved its usefulness in the determination of the Earth’s [anonimizat], [anonimizat], etc.

A particularly important emphasis is placed on the country's [anonimizat], for an information supplement in order to clarify the geodynamic context in which the crustal and subcrustal tensions in the region's lithosphere accumulate.

[anonimizat], which come into contact with this area located at the Oriental Carpathians curvature.

[anonimizat] only has been accomplished over the years through major international research projects, as they are below described.

GPS Studies in Romania – The Beginnings

The first applications using GPS technology on the Romanian territory were made in 1994 under the auspices of the U.S. National Geodetic Survey (NGS) – and with the participation of the Romanian Ministry of Agriculture (), former Institute of Geodesy, Cadastre, Photogrammetry and Cartography (ICGFC, formerly IGFCOT) and the Direction of Military Topography (DTM).

All observations were conducted in 7 locations (Constanța, Dealul Piscului, Moșnița, Osorhei, Sfântu Gheorghe, Sirca and Stănculești) considering the standard precision allowed for the NGS A order – (5 mm 1: 10,000,000). Geographical locations of the observatories were primarily made considering the uniformity distribution criterion in the territory; at each observation point there was also a first degree geodetic point.The main station is located in the proximity of the MilitaryAstronomical Observatory  (Dealul Piscului –Bucharest) and was set up as the origin for the entire Romanian network for further GPS data processing.

The observation data processing was performed at NGS (Silver Spring, Maryland) using 4 different measuring time intervals (i.e. 26 September 1994, 0900 UTC on 27 September 1994, 0900 UTC) by the aid of a specialized S software installed on an HP 9000/700 working station [1]. All computed coordinates for the observation stations have been determined in the ITRF92 – 1994.7 system.

The coordinates of the network main station (Dealul Piscului) were determined by using the spatial positions of the three support points (ONSA, MADR, WETT – GPS permanent stations) for every time interval of the four observation measurements.

The four data sets average was considered to be the final set of coordinates in the ITRF92 – 1994.7 system. Once the coordinates of the Dealul Piscului point have been fixed, they were used to add more measurement points to the network by calculating the position of the other stations reported to the coordinates of the reference point.

The CERGOP Project

GPS geodetic satellite studies in Romania have been continued in 1995 as part of an international european project, OP (Central European Geodynamic Project) designed for geodynamic research in Central and Eastern Europe.The CEGRN geodetic network (Central European GPS Geodynamic Reference Network) was materialized in 1994 and originally covered the territories of the ten countries – Austria, Czech Republic, Croatia, Germany, Italy, Poland, Slovakia, Slovenia, Ukraine and Hungary, consisting of 31 GPS benchmarks.

The initial CEGRN network on the Romanian territory was formed of 5 benchmarks located along the Carpathian Orogen area (Tismana – TISM, Fundata – FUND, Vrancea – VRAN, Vatra Dornei – VATR and Gilău – GILA), one benchmark in the Northern Dobruja – Orogen (Macin – MACI), one in the Moldavian Platform (Iasi – IASI) and the last one in the Moesian Platform (Măgurele – MAGU, in the southern part of Bucharest city) (Fig. 1).

In this geodetic network satellite observations during the years 1995, 1996, 1997, 1998 and 2001 have been performed. All observation equipment – SSE and SSI Trimble GPS receivers – were made available by partners of the German Federal Agency for Cartography and Geodesy (Frankfurt am Main).Field measurements were carried out by German specialists from the University of Karlsruhe and the Romanian specialists from the Faculty of Geodesy and the National Institute for Earth Physics in Măgurele.The Romanian CEGRN network was completed in 1997, 2000, 2002 and 2003 in the frame of CERGOP – 2 Project, targeting the movements monitoring the Vrancea seismogene area in the first decade of the 21st century.

Here it can be concluded that the calculated relative speeds are very small, on the order of 3 mm/year, with the remarkable exception of IAS3 and TIS3 locations, but here the approximately high observed values could be explained by the influence of the eccentricities which have seriously affected the measurements. Regarding the vertical movements’ calculations there were compared by using a Helmert transformation the computed campaigns solutions with an average solution according to the 1995.89 epoch.It can be easily seen that the movements recorded on the vertical component have generally low values, on the order of ± 5 mm for the considered time span.

Fig. 1. The CEGRN Geodetic Network in Romania – ,

– GPS observatories, ○ – towns.

However, these values are comparable to the noise level affecting the vertical component and, even if it might highlight certain tendencies of movement, they are difficult to confirm because of the relatively short period of time for which the analysis was carried out.The estimated noise level, about 10 mm, was surpassed only in the case of VRAN and VATR stations.It can be concluded from these determinations that both the horizontal movements and the vertical ones are highly comparable to the noise level and are not significant [2].

GPS Studies in the Vrancea Area

Since 2001 the GPS measurements in the Vrancea network were carried out within the framework of the research project SUBDUCT (Surface Behaviour and Dynamical Units of the Southern Carpathians Tectonics) initiated by the Dutch Centre for integrated research on Solid Earth Science (ISES) and the University of Delft (Netherlands) [3].

The goals of the project have been fulfilled in collaboration by the Romanian experts belonging to the Faculty of Geology and Geophysics from the University of Bucharest and the National Institute for Earth Physics. The main objective of the project was related to the monitoring, analysis, and interpretation of surface movements caused by the dynamics of the lithosphere crust – active in the region of Vrancea (South Eastern Carpathians) [4].

The SUBDUCT project was accomplished in collaboration with the Institute of Geodesy in Karlsruhe (Germany), which led another international programme, namely 461 – "Strong Earthquakes: A Challenge for Geosciences and Civil Engineering"; this program involved GPS data acquisition for the region under investigation, starting from 1997, when 28 GPS points were installed, covering an area of 350 x 350 km2 located in eastern part of Romania, centered on the Romanian most important seismic area (Fig. 2).

Fig. 2. The Vrancea GPS network, – GPS observatory belonging toVrancea network,

– GPS observatory belonging to CEGRN network, ♦ – GPS observatories not included in Vrancea network, ○ – towns.

This geodetic network has been measured over the period of time 1997 – 2004 by the Dutch specialists of the University of Delft, as well as by the specialists of the German Institute of Geodesy from Karlsruhe and specialists of the Romanian National Institute of C-D for Earth Physics [5].

The Vrancea network was composed of 54 GPS measurement points, of which 6 permanent stations, measured between 2001 and 2004.

In all measurement campaigns Leica XRS – 1000 GPS receivers with antennas AT – 504 were installed. There were performed seven measurements campaigns (1997, 1998, 2000, 2002, 2003, 2004 and 2006) until 2006 using Leica receptors 300 & 500 and the corresponding antennas.

The GPS studies carried out during 1995 – 2004 have provided useful information on local tectonic movements in the Carpathians Arc bend, characterized by lower values, less than 1 mm/year for the horizontal component and 3 mm/year for the vertical component.

There were observed two main movement directions, in the Dobrujan domain of the Moesic Platform (between Peceneaga Camena and Intramoesian fault lines), to the SSE, with 2.5 mm/year average velocities and in the Vallachian domain of the Platform, to the S, in the range of 1 – 2 mm per year.

These data have revealed dextral movements, along the Intramoesian fault, with a rate of 1 – 2 mm/year, in accordance with the values obtained from seismic and geological studies concerning the Pliocene – Quaternary formations kinematics.

A significant change in the horizontal direction of the movements occurs near the Southern boundary of the Moldavian Platform (the Eastern sector of East – European Platform), besides the Trotuș Fault.

GPS data have shown a senestral sliding domain, also highlighted in geological and neotectonic studies; the latter have revealed the existence of a NW – SE orientated corridor inside that senestral deformations took place in the period of time associated with upper Miocene – Quaternary [5].

The above mentioned corridor is separating the stable or raising areas belonging to the Scythic domain and the East European Platform from the subsidence and the SSE movements areas belonging to the Focsani depression.

From the vertical movements point of view it has been revealed the existence of alternative lifting and sinking areas (subsidence) in the South – East part of the Eastern Carpathians, with NW to SE orientations.

The subsidence areas overlap on the Focșani and Brașov basins with considerable accumulation of Pliocene – Quaternarysediments.

The most significant subsidence observed in the Focșani depression has indicated vertical speeds in the range of 2 – 3 mm/year.

The subsidence trend is common to the eastern sector of the Moesian Platform, but with much reduced values compared to those observed in the Focșani – Odobeștiarea.The PerșaniMountains area, located in the South – EasternCarpathians, which corresponds with the most significant lifting movements domain, during Pliocene – Quaternary, is highlighted between all lifting areas.

The high speeds recorded within the vertical movements revealed at the Carpathians' curvature probably indicates the lowering of the litospheric plate in this region, whose displacement is responsible for the subcrustal activity in the Vrancea region.

According to [5], it appears to be possible that the time series analysis might be too short for a realistic interpretation of the geodynamic results; future campaigns will improve performances through an increase in the accuracy with which both horizontal and vertical velocities are determined from this very important tectonic area of the Carpathians.

In a PhD Thesis elaborated by one of the authors of this article the crustal strain analysis in an extensive network based on GPS measurements carried out in two measurement campaigns (1998 and 2000) has been discussed [6].

The geodetic network was made up of 35 benchmarks located both in the Orogenic area (16) and in the Vorland area (19, in the Carpathian Foredeep, Moesian Platform, Moldavian Platform and TransylvanianBasin).This analysis was performed using the Finite Element Method (MEF).

In the case of geodetic measurements the finite element type has been chosen as the triangle shape, as close as possible to the equilateral triangle which represents a theoretical constraint, defined in a two – dimensional space represented by the land area between the considered GPS benchmarks.

The computing of the deformation parameters (strains) inferred only from geodetical measurements shall be made on the basis of the knowledge of the analysed points position at least in two different epochs or by knowing of the movement speeds of the finite elements’ nodes.

In the extended Vrancea network the strain parameters for all those 42 finite elements which forms the network’s mesh were computed; the section under investigation covered an area marked out by Bucharest – Pitesti – Tg. Mures – Galați – Bucharestcities.

For each finite element the directions for the main maximum and minimum strains have been mapped out. It should be noted here that always, by convention, positive values are assigned to extensions (dilatations) and negative values to compressions.

The computation of the strain parameters’ values have enabled the development of two crustal strain maps of the area, namely the Vrancea extended network.Thus, one may notice that 90% of the values of maximum principal strain 1 are positive, extensional, and those belonging to the minimum principal strain 2 are mainly negative, with a compressional behaviour.

Another significant observation that could be made is the correlation between the area of intense crustal seismic activity and the strong anomalies emphasized in the crustal strains.

The short time period of only 2 years which was the subject of the study has strongly influenced the quality of the analysis, highlighted by the absence of any spectacular phenomena in the crustal strain analysis; more conclusive results will be obtained from tests carried out for longer periods of time.

Newly Installed GNSS Stations after 2012

The permanent stations network in Romania was initiated in 2001 by the first GPS Observatory installed in Lăcăuți. The network was designed with respect to the idea of constantly adding of new stations, for national general targets; 24 stations are in use so far (Fig. 3) and other stations are planned to be installed in the next future.

Fig. 3. Romania's NIEP permanent stations network,

– GNSS measurement observatory, ○ – towns.

The main purpose of the measurements is related to the three-dimensional monitoring of crustal movements with high accuracy required by fundamental geodynamic research necessary for the national territory where are not highlighted significant displacements. As the newly installed stations are in operation for only a short time, data analysis have not been tried yet, as it requires a longer working time to ensure that the data provided will enter the required precision.

CONCLUSION

After this brief retrospective of the activities which involve the use of the space geodesy techniques in Romania it can be concluded that their development was very strong, starting from experimental works using an insignificant number of observatories, to networks of tens, even hundreds of measurement points, in the most diverse types of activities.

The explosive development of space geodesy techniques has imposed both the numerical increasing of measurement observatories and their endowment with modern equipment using the latest technology.

Thus, a spectacular progress has been made from measurements campaigns carried out in small networks for strictly specific goals, lasting only a few days, such as geodinamic polygons to measurements performed in regional and national network of permanent stations, with impressive amounts of data, delivered by telemetry systems to a unique processing centre.

The equipment used in present days allows to increase the measurement precision to unthinkable values with some time ago, being thus possible millimeter accuracy.

Another very important applicability domain of global positioning techniques is related to the real time position determining of moving vehicles, whether we are talking about a car, ship or aircraft, in strictly specialized areas which require a very good equipment endurance.

Without having the claim to deplete the vastness of proposed subject, it can be concluded that the entire life and modern technology is highly addictive to the exact determinations of the point position as a result of the satellite geodesy techniques.

Acknowledgments

This paper was carried out within "Nucleu Program MULTIRISC", supported by MCI – Romania, project no.PN19080201 andProject no. 18PCCDI/2018, supported by UEFISCDI – Romania.

References

[1] Schenewerk, MS., S – PAGE4 users manual. OES Internal Document, NOAA, Silver Spring, MD, 1993.

[2] Ghițău D., Gavrilescu M., Nacu V., Dumcu D., Năstase F., Mateciuc D., National Progress Report of Romania for CERGOP, for the 2nd CERGOP-2/Environment Working Conference, Warsaw, Poland, 2003.

[3] Ambrosius B.A.C., van der Hoeven A.G.A., Mocanu V., Munteanu L., Spakman W., Schmitt G., Ten Years of GPS Observations in Romania, J. Balkan Geophys. Soc., 8, suppl. 1, pp 197 – 200 pp, 2005.

[4] Zoran M., Mateciuc D., ner J., Ciucu C., Spatial techniques for investigating seismic areas (in Romanian), Conspress Publishing, Bucharest, Romania, 230 pp, 2008.

[5] Van Hoeven A.G.A., Mocanu V., Spakman W., Nutto M., Nuckelt A., Matenco L., Munteanu L., Marcu C., Ambrosius B.A.C., Observation of present-day tectonic motions in the Southeastern Carpathians: Results of the ISES / CRC-461 GPSmeasurements, Earth and Planetary Science Letters 239, 177 – 184 pp, 2005.

[6] Mateciuc N. D., Contributions to the knowledge of crustal deformation field in Romania (in Romanian), PhD Thesis, Fac. of Physics – Bucharest University, 234 pp, 2010.