THE XIV-th SYMPOSIUM OF EARTH'S PHYSICS
AND APPLIED GEOPHYSICS

The Academy of the Socialist Republic of Romania, in cooperation with the Ministry of Mines, Oil and Geology, organized the XVIth Symposium on Earth's Physics and Applied Geophysics between 2 and 4 July, 1987.
In the opening session, chaired by acad. Sabba Stefanescu, after the address given by acad. Radu Voinea, President of the Academy of the socialist Republic of Romania, acad. Sabba Stefanescu, President of the Section of Geological, Geophysical and Geographical Sciences of the Academy of the S.R. of Romania and dr. Ioan Folea, Minister of Mines, Oil and Geology underlined in their speeches the significance of the Symposium wishing its proceedings full success.
The proceedings of the Symposium developed within three sections:
– Geophysical investigation for energy resources and engineering geophysics (chairman professor Radu Botezatu, corresponding member of the Academy);
– Geophysical investigations for solid mineral substances (chairman acad. Sabba Stefanescu);
– The Earth's physics and geodesy researches (chairman professor Liviu Constantinescu, corresponding member of the Academy).
Simultaneously, an exhibition of posters was organized, in which some of the latest achievements in the field of geophysical researches were presented and the main stages of acad. Sabba Stefanescu's activity were emphasized.
The working sessions were followed by discussions in which the full members of the Academy and numerous representatives of the research and production sectors and higher education institutes from Romania took part. The proceedings were officially closed by acad. Sabba Stefanescu. Subsequently acad. Radu Voinea, the President of the Academy of the S.R. of Romania, pointed out that the presence in the Assembly Hall of the Academy of the elite of Romanian specialists in geophysics is a good opportunity to celebrate the 85 years of life and 60 years of fruitful scientific activity of acad. Sabba Stefanescu.
The address given by acad. Radu P. Voinea, the President of the Academy of the S.R. of Romania, was published in the tome 31, 1987 of the journal "Revue roumaine de géologie, géophysique et géographie – Géophysique", an issue which was dedicated to acad. Sabba Stefanescu's birth anniversary.
In this issue for lack of printing space we cannot publish in extenso all the presented works. In order to inform interested specialists, unable to participate in the Symposium proceedings about the main development directions of scientific researches in the fields of Earth's physics and applied geophysics, we publish the abstracts and keywords of the presented papers.

OPENING SESSION

Chairman: Acad. SABBA STEFANESCU

SEISMOTECTONIC AREAS IN ROMANIA AND JAPAN
GEODYNAMICAL AND SOCIO–ECONOMIC ASPECTS

I. CORNEA
Center for Earth Physics and Seismology, Bucharest – Magurele

A comparative study of the active tectonic zones in Japan and Romania shows similarities and differences, whose explanation is related to the different ages of the corresponding geological formations. Specific geodynamical aspects and socio-economic implications of the volcanic and seismic activities are studied.
Technical equipment and particular trends of geophysical research in both countries are also presented.
Key words: seismotectonic, Romania, Japan, socio-economic aspects.

THE PRESENT PHASE OF THE GEOPHYSICAL
EXPLORATION METHODS FOR RADIOACTIVE MINERALIZATIONS

V. GEORGESCU, R. CONSTANTINESCU
Enterprise of Rare Metals, Bucharest

The paper considers the latest developments of the radiometric methods concerning the field working method, the processing of the measurement data as well as the interpretation of the results.
The possibilities of using non-radiometric geophysical methods in the exploration for the radioactive mineralizations, are printed out.
Key words: radiometrical exploration method for radioactive mineralizations, treck-etch, ray spectrometry, useful signals, background noise.

GEOPHYSICAL INVESTIGATIONS FOR ENERGY RESOURCES
AND ENGINEERING GEOPHYSICS

Chairman: prof. RADU BOTEZATU, corresponding member of the Academy

UTILIZATION OF REFLECTIONS SEISMICS IN
ENGINEERING GEOLOGY (HISTORY CASE)

V. VARODIN, CALIN POPESCU, D. POPESCU, C. POPESCU, M. VOINEA, D. ROSCA
Enterprise of Geological and Geophysical Surveys, Bucharest

The paper shows a seismic surveying made in order to outline the shallow tectonics useful in solving an engineering geology problem.
Some processing parameters were set up to obtain a high resolution of seismic data – very important in shallow seismics.
The output of these seismic surveys is represented by migrated time section geologically interpreted and structural maps.
Key words: engineering geology, shallow tectonics, processing parameters, high resolution, migrated time section, structural maps.

CROSSLINE STATICS ESTIMATION FOR 3D SEISMIC

LILIANA BADESCU, ELENA CHISCAN, I. HARABOR, N. MOLDOVEANU
Enterprise of Geological and Geophysical Surveys, Bucharest

This paper studies on synthetic data the method of correlation time surface for estimation of crossline statics. We conclude that this method could be used for improving the final results of 3D seismic prospecting.
Key words: surface, time correlation, statics corrections, 3D.

SAMPLING OF THE 2D SEISMIC DATA

V. BARDAN
Enterprise of Geological and Geophysical Surveys, Bucharest

This paper applies the 2D signal theory to obtain results concerning the sampling of seismic data (trace interpolation, of spatially aligned data, triangular sampling and sampling requirements for numerical evaluation of the Radon transform).
Key words: 2D signal, sampling, seismic data, trace interpolation, triangular sampling, Radon transform.

INVERSE SCATTERING FOR 1D DISCRETE SEISMIC MODELS

V. BARDAN
Enterprise of Geological and Geophysical Surveys, Bucharest

This paper treats the inversion of the seismogram for a horizontally layered earth (Goupillaud model) and obtains a unified, straightforward approach for a lot of inverse 1D discrete scattering problems arising in various fields. In this approach it is shown how the direct exploitation of wave propagation equation leads to recursive, efficient and reliable inversion algorithms.
Key words: inverse scattering, 1D discrete seismic model, Gupillard model, unified approach.

MINIMUM PHASE FOR CONTINUOUS TIME
AND DISCRETE TIME FUNCTIONS

V. BARDAN
Enterprise of Geological and Geophysical Surveys, Bucharest

Keeping the mathematics within the realm familiar to geophysicists the paper explains why the sampling operation – i.e., the change from the continuous time domain to the discrete time domain – does not necessarily preserve the minimum phase.
Key words: minimum phase, continuous time function, sampling, discrete time function.

DIP NMO MOVEOUT

N. MOLDOVEANU, ELENA CHISCAN
Enterprise of Geological and Geophysical Surveys, Bucharest

For area with complex tectonics CDP stack does not work properly because it discriminates between conflictual dips. One solution for improving the results of CDP stack is NMO moveout correction that depends on dips.
Key words: correction, NMO, dip.

VELOCITY AND PRESSURE ANOMALIES AS POSSIBLE
LITHO-STRATIGRAPHIC TRAPS FOR HYDROCARBONS
IN MOESIC PLATFORM FORMATIONS

A. DAMIAN
Enterprise of Geological and Geophysical Surveys, Bucharest

Sonic and seismic log information in addition with other types of log information show small velocity anomalies (undercompaction) in Upper Triasic marl-limy complex from the south-eastern part of the Moesic Platform and in Pontian marls from the north-eastern part of the same unit.
Key words: (Velocity, pressure) anomaly, litho-stratigraphic trap, overburden, undercompaction, interval travel time, interval velocity.

ELECTROMETRIC DATA COMPUTATIONAL PROCESSING
METHODS USED IN ANTHRACITE LAYERS DETERMINATIONS

VIORICA CONSTANTINESCU, V. CONSTANTINESCU, A. VLAD
Enterprise of Geological and Geophysical Surveys, Bucharest

the results obtained "in situ" measurements showed that between Schela formations (with anthracite) and the other formations (sedimentary and crystalline) strong contrasts of electrical properties are presented. To make evident Schela formations IP measurements in time domain and Vertical Electric Sounding were used.
Computational processing allowed the analysis of the IP discharge curves shape and the current lines (Baranov methods). This methods gave very conclusive results.
Key words: measurements, Schela formation, contrasts of electrical properties, IP discharge curves, Vertical Electrical Sounding (SEV).

ANALOGIC BLOCK OF A SEISMIC ACQUISITION SYSTEM

H. POPESCU, I. POP, V. IONESCU, M. ROMAN, A. VLAD
Enterprise of Geological and Geophysical Surveys, Bucharest

The analogic block of a seismic field acquisition system comprises the following building blocks: preamplifer, filter (low cut, 50 Hz rejection, antialiasing), buffer multiplexer and instantaneous floating point amplifier.
We present a solution that offers multiple possibilities of choosing the operating parameters.
Key words: multiple remote selectable cutoff frequencies, controlled reject frequency, instantaneous floating point amplifier.

LOOKING AHEAD AFTER 2000 WELL OPERATIONS
BY THE D.R.R. LOGGING METHOD

V. NEGOITA
Oil and Gas Research Institute, Campina, Prahova County, Romania

The use of the D.R.R. well logging method during the last 17 years totalized 20 00 well operations whose main applications in petrophysics, sedimentology and fluid drilling optimization are syntethized.
The final part of the paper is dedicated to the future applications in the domain of well logging prospecting.
Key words: D.R.R. well logging, petrophysics, sedimentology, fluid drilling, well logging.

PRESSURE-TEMPERATURE-DENSITY-WATER FILLING
PORE SPACE INTERRELATIONS AND THEIR IMPLCIATIONS
IN HYDROCARBON MIGRATION. APPLICATIONS ON THE
ROMANIAN TERRITORY

V. NEGOITA
Oil and Gas Research Institute, Campina, Prahova County, Romania

The paper presents the relations between pressure, temperature, density and water filling pore space needed for the determination of fluid expulsion from rocks and the knowledge of hydrocarbon migration directions. Finally some applications on the Romanian territory are exposed.
Key words: pressure, temperature, density, rock porosity, hydrocarbon migration.

THE USE OF GEOPHYSICAL WELL LOGS FOR
SEDIMENTATION ENVIRONMENTS RECOGNITION

A. NEGUT, C. DINU
Faculty of Biology, Geology and Geography, The University of Bucharest, Bucharest

The main patterns of different facies and sedimentation environments reflected on geophysical well logs are presented in the paper. The applications of these patterns and implications for hydrocarbon potential evaluation of investigated geological formations are discussed on some cases.
Key words: geophysical logs, facies, sedimentation environments.

THE INFLUENCE OF MUD FILTRATE INVASION ZONE
DIAMETER ON AMPLITUDE OF SP CURVE

I. MALUREANU
The Oil and Gas Institute, Ploiesti

The physical model used for SP curve interpretation assumes the location of double-electric layers on the well wall. In fact as porous-permeable formations level, the position of double-electric layers varies with the invasion zone diameter.
A qualitative and quantitative evaluation of invasion zone diameter influence on static and recorded SP, with practical implications on bed thickness and resistivity of formation waters determination are presented in the paper.
Key words: spontaneous potential (SP), invasion zone, resistivity of formation waters.

CEMENT BOND LOG FOR WELLS CEMENT JOB
QUALITY EVALUATION

S. BANDI
Oil and Gas Designing and Research Institute, Bucharest Research Department, Bucharest

This paper represents the definite solution of the correct investigation problem, the answer to the question: was the cement job a good or a bad one?
Both the reliable logs and the new interpretation procedure represent the warranty of the minimum predicted isolation interval that necessarily exists between two perforations, so that there will be no fluid communication behind cemented casing.
Key words: amplitude, acoustig signal, attenuation, cement bond, compressive strength, isolation interval.

DENSITY LOG IMPLCIATION IN LITHOLOGY
DETERMINATION AND GAS IDENTIFICATION

S. BANDI
Oil and Gas Designing and Research Institute, Bucharest Research Department, Bucharest

By applying the correct calibration so much different from the two Dresser Atlas calibrations recommended in Operating instructions, the Compensated Densilog tool reaches the highest performances becoming a reliable instrument along with Compensated Neutron Log, in lithology determination and gas identification: the high precision of rock's density measurement assures the most correct porosity value determination.
Key words: bulk density, porosity, overlay logging, gas/oil contact, gas/water contact.

RESISTIVITY METHOD WELL-LOGGING EQUIPMETNS

A. BABSKOW, M. BANU, N. NITU, C. VIJIAC
The Design and Research Institute for Oilfield Equipment, Ploiesti

The resistivity method well-logging equipments are presented, constituted of:
– resistivity panel,
– induction logging bore-hole tool with two diameters: (70 mm and 86 mm),
– electrical focused logging tool (laterolog – 3).
The bore-hole tools furnish the electrical signals, proportional to the conductivity of the rocks passed through by the bore-hole, both by the induction current procedure, or the electromagnetic field propagation respectively, and by the focused current procedure. They work in the following environmental conditions: temperature 125 – 150 °C and pressure 100 – 120 MPa.
The bore-hole tools contain: the electronic section and the transducer sections:
– coil section, for induction tool,
– current and focusing electrodes, for laterolog-3 tool.
The resistivity panel processes, the conductivity signals and transforms them into resistivity signals, by means of a reciprocator system, consisting of a logarithmic and exponential amplifier assembly. The skin-effect correction – affecting the induction conductivity signal – is made.
Key words: induction log, focused log, laterolog-3, resistivity, conductivity, coil section, current electrode, focused electrode, logarithmic amplifier, exponential amplifier, reciprocator, skin-effect.

GEOPHYSICAL INVESTIGATIONS FOR SOLID MINERAL SUBSTANCES

Chairman: Acad. SABBA STEFANESCU

GEOPHYSICAL AND GEOCHEMICAL IMAGES
OF THE MAGURA TEBII MINING FIELD

J. ANDREI, M. BRADU, SIMONA BRADU, D. CONSTANTINESCU, Z. IOANE,
T. NESTIANU
Institute of Geology and Geophysics, Bucharest

The gravimetrical, magnetometrical, radiometrical, gamma, mercurometrical and pedogeochemical images (Pb, Zn, Cu, Ag, As) in the Magura Tebii area bring out a series of interesting information regarding the structure of Neogene volcanites, as well as the distribution of the associated hydrometamorphic and metallogenic products. The corroboration of the above-mentioned data with the geological information allows a better evaluation of the geoeconomic perspectives of the Magura Tebii mining field.
Key words: magnetometry, radiometry, mercurometry, pedogeochemistry, hydrometamorphism, metallogenesis.

A GRAVITY MODEL OF DOBROGEA

V. ROSCA, LIGIA ATANASIU
Institute of Geology and Geophysics, Bucharest

Using a configuration of upright rectangular prisms, the main regional gravity anomalies, known on the Dobrogea territory, have been reproduced. As a main result of this modelling procedure, it has been shown that the observed gravity variations could be explained by density contrasts situated inside a crust stratum limited to a depth of 5 km.
Key words: Dobrogea, model, gravity.

GRAVIMETRIC AND MAGNETOMETRIC CONTRIBUTIONS
IN DETERMINING THE DEEP STRUCTURE OF THE
SOUTHERN FAGARAS MOUNTAINS

AL. PETRUT, ANA TUDOR, D. TUDOR, EMILIA PETRUT, R. VELICU
Enterprise of Geological and Geophysical Surveys, Bucharest

The structural relations among the various types of crystalline series are determined clearing up the evolution of the crystalline relief under the sedimentary deposits.
The tectonic alignments are rendered evident and some information is got concerning the deep structure of the researched area.
Key words: The Southern Fagaras Mountains, structural relations, gravimetry, magnetometry.

STRUCTURAL ASPECTS OF THE DITRAU ALKALINE MASSIF
BY GRAVITY AND MAGNETIC INFORMATION

ADRIANA POSTOLACHE, C. POSTOLACHE, V. MOCANU
Enterprise of Geological and Geophysical Surveys, Bucharest

The purpose of this paper is to point out and discuss the correlation of the gravity, magnetic and geological data for trying to explain the new structural elements of the Ditrau alkaline massif. Special attention is paid to the Güdücz complex and its image in both potential fields.
Key words: Ditrau, Güdücz, gravity, magnetic, structural.

ABOUT SOME INVERSE MAGNEIZATION IN THE
ERUPTIVE NEOGENE AREA OF GUTAI MOUNTAINS

I. MIHUT, DONA MIHUT
Enterprise of Geological and Geophysical Surveys, Bucharest

Gutai Mountains, an area of neogene volcanaites, presents some inverse magnetization phenomena. In Ilba region (Baba Griga valley and Lajos hill), inverse magnetization was studied by the local geomagnetic field component, the micromagnetic and vertical gradient of magnetic field.
Key words: Gutai, Baba Griga, Lajos, inverse magnetization.

THE GRADIENT METHOD APPLIED
IN WEAK MAGNETICAL SIGNAL ZONES

GH. MATEESCU, D. ONESCU, CARMEN DUMITRESCU
Institute of Geology and Geophysics, Bucharest

The measurements of vertical magnetic gradient made in two zones of the South Metaliferi Mountains in a network of microdetail (2 x 2 m) have proved the applicability of this methodology in magnetic fields with weak signal. We intend to compare the measured gradient with the gradient resulting from the automatic processing of the data through numerical analysis in the spectral and spatial domain.
The results of the research may constitute a current method for the practical magnetic prospecting.
Key words: magnetic gradient, weak magnetic signal, numerical analysis.

STRUCTURAL GEOLOGICAL ELEMENTS OBTAINED
BY MAGNETOMETRIC PROSPECTING IN THE LEAOTA MOUNTAINS

R. CRAHMALIUC, ANCA CRAHMALIUC
Enterprise of Geological and Geophysical Surveys, Bucharest

The elements deduced by magnetometric anomalies analysis, petromagnetometric determinations and the latest geological data, led to the improvement of the structural model of the crystalline formations in the Leaota Mountains.
A correlation is tried of the model with the direct information, obtained from structural drillings in the area, as well as with data provided by other geophysical methods.
Key words: crystalline formations, structural model, petromagnetic determinations, magnetometric anomalies, structural drilling.

MAGNETIC MINERALS FROM MESOZOIC MAGMATITES
IN THE METALIFERI MOUNTAINS, IMPLICATIONS
IN ROCK MAGNETIZATION AND ROCK SYSTEMATICS

D. ONESCU, PARASCHIVA ONESCU
Enterprise of Geological and Geophysical Surveys, Bucharest

The study presents the connection between distribution shape, size and chemistry of the titanomagnetic, illmenite, maghemite grains of the Mesozoic magmatic rocks in the Cazanesti – Godinesti – Vorta – Dealul Mare area (Metaliferi Mts) and their magnetic properties.
In conclusion, a new model regarding the systematics of different rock types is presented.
Key words: distribution shape, size and chemistry of magnetic minerals, magnetic properties, Mesozoic magmatites Metaliferi Mts.

GEOLOGICAL CONTRIBUTION TO THE PROSPECTING
OF LEAD-ZINC MINERALIZATION VORTA TYPE– METALIFERI MOUNTAINS

M. MUNTEANU, GH. BICHIR
Enterprise of Geological and Geophysical Surveys, Bucharest

The paper presents the results obtained through induced polarization (time and frequency domain) and resistivity for identification of lead – zinc mineralization and geological structure.
Key words: induced polarization resistivity, lead-zinc mineralization, geological structure, Metaliferi Mountains.

VERTICAL ELECTRIC SOUNDINGS APPLIED TO DISCOVER
THE STRUCTURE OF THE SEDIMENTARY BASIN
FROM BARSA AND VAD-BOROD DEPRESSIONS

V. FILIPCIUC, M. C. VISARION
Enterprise of Geological and Geophysical Surveys, Bucharest

The paper is an account of the data obtained by using the VES resistivity methods applied to the investigation of the intramountainous basins. These basins include Neogene formations (some of them coal bearing ones), which overline a resistive basement.
The data reported for the Barsa and Vad-Borod depressions prove that this geoelectrical method may be successfully used for pointing out the relief and the tectonic features of the basement.
Key words: resistivity, vertical electric sounding, structural model, system of faults.

DETERMINATION POSSIBILITIES OF ELECTRODE ARRAYS
INFLUENCE ON INDUCED POLARIZATION ANOMALIES
BY USING PHYSICAL MODELING

M. JOSAN, I. CORCIMARU, R. MIHALACHE
Enterprise of Geological and Geophysical Surveys, Bucharest

Using three-dimensional physical models, it was possible to point out in the I.P. anomalies, specific elements according to the studied modeling, depending on disposing the electrode-arrays (gradient, VES and dipole-dipole arrays).
Key words: physical modeling, I.P., three-dimensional.

RESULTS OF MODELING THE RESISTIVITY ANOMALIES
DUE TO BIDIMENSIONAL BODIES BY USING
THE FINITE ELEMENT METHOD

F. SCURTU, GABRIELA CUCU
Institute of Geology and Geophysics, Bucharest

An efficient method for modeling the geoelectric anomalies is the finite element method. The computing program created with this end in view was checked on several cases with good results presented in this paper.
Key words: geoelectrical anomaly, finite element method, computer, modelling, 2D body.

HYDROGEOLOGICAL ZONES MODEL ESTABLISHED WITH
THE HELP OF VERTICAL ELECTRICAL SOUNDINGS
IN BALACI – ROSIORI DE VEDE – ALEXANDRIA ZONE.
TELEORMAN DISTRICT

RUXANDRA SLAVOACA
Enterprise of Geological and Geophysical Surveys, Bucharest

This paper presents a hydrogeological zones model, established with the help of vertical electrical soundings, having in view to point out the extension of the aquiferous complexes included into Quaternary and Romanian sedimentary formations in Teleorman district.
Key words: hydrogeological division into zones, aquiferous complexes, vertical, electrical soundings.

THE GEOLOGICAL AND GEOPHYSICAL ASPECTS FROM
THE STREI BASIN (BETWEEN THE STREI RIVER AND GRID PEAK)

TH. CRISTESCU, M. CENGHEA, D. DOROS, C. MIHUL, M. SUCEAVA
Enterprise of Geological and Geophysical Surveys, Bucharest

Geophysical data obtained from the East of the Strei River allowed to draw up the structural model of the crystalline basement – Poiana Rusca type, in correlation with the previous, geological information, for directing the research program of the iron mineralizations, chromatic type.
The geological results and petromagnetic data obtained by the first drillings performed to the South of Strei-Sangeorgiu are presented.
Key words: crystalline basement, structural model, petromagnetic data, Strei-Sangeorgiu, Grid peak.

ANALOGICAL AND DIGITAL PROCESSING OF REMOTE
SENSING IMAGERY IN THE FIELD OF GEOSCIENCES

V. VAJDEA, C. NITICA, D. ZORILESCU, I. POPESCU,
ALEXANDRA MARINESCU, DANA FEKETE
Institute of Geology and Geophysics, Bucharest

Various examples of analogical and digital processing of satellite and areal remote sensing imagery recorded over the territory of the S.R. of Romania are presented. The results of these processing have supplied important geologic information: tectonics, accidents, mapping, delimitation of main geologic units and formations, igneous bodies identification and localization, sedimentary processes tracing etc.
Key words: imagery, analogical processing, digital processing, geosciences.

CONTRIBUTIONS OF THE REMOTE SENSING TO THE PROGNOSIS
OF FAVOURABLE AREAS FOR MINERAL RESOURCES ACCUMULATION

V. VAJDEA, C. NITICA, D. ZORILESCU, ANCA-MARIA VAJDEA, VL. GANCZ
Institute of Geology and Geophysics, Bucharest

This paper presents the possibility of using remote sensing data for the prognosis of the favourable areas for mineral resources accumulation on geostatistical basis. Special attention has been paid to algorithms and automatic data processing programmes. Their testing in case of some metallogenetic units in the S.R. of Romania proves the practical utility of this new method in solving such problems.
Key words: remote sensing, prognosis, geostatistics, automatic processing, metallogenetic units.

UTILIZATION OF VIBROSEIS SYSTEM IN SURVEYING AREAS COVERED
WITH VOLCANIC ROCKS AND DETECTING SOLID MINERAL SUBSTANCES

V. VARODIN, I. C. BUCUR, I. VILCU, R. BOTEZ
Enterprise of Geological and Geophysical Surveys, Bucharest

This paper shows the possibility of obtaining seismic information concerning the contouring of intrusive bodies by using a Vibroseis system. The technology used in data acquisition was set up to check the extension of the sedimentary under the andesite plate without a special pursuit of the identification of intrusive bodies. The migrated time section was interpreted on a geological model.
Key words: intrusive bodies, Vibroseis system, data acquisition, migrated time section.

PETROPHYSICS OF FAGARAS MASSIF

V. STOENESCU, DR. ROMANESCU, ELENA SZABO, ANCA GEORGESCU
Institute of Geology and Geophysics, Bucharest

All types of rocks belonging to the Fagaras, Cumpana and Leaota groups, comprised between Old Valley to the West and Dambovita Valley to the East are presented from the magnetic and density point of view.
Some magnetic active schists were discovered. Four types of amphybolites, depending on magnetic susceptibility, are pointed out. The density study shows a high mean density value of the rocks from the Fagaras group.
Key words: density, magnetic properties, metamorphic rocks, Fagaras massif.

PETROPHYSICAL DATA IN CALIMANI MASSIF

DR. ROMANESCU, I. SEGHEDI, V. STOENESCU, ELENA SZABO,
ANCA GEORGESCU
Institute of Geology and Geophysics, Bucharest

Petrophysical researches in the Calimani massif allowed the characterizing, of all types of rocks forming these mountains, as well as the drawing up of density, magnetic susceptibility and Q factor profiles and maps.
An increase, from the South to the North, of the density and magnetic parameters values of igneous rocks s to be noticed.
Some zones affected by endogene transformations and others with a higher content in magnetite are pointed out.
The emplacement mode of some andesites and the origin of some volcanoclastites have been established.
Key words: density, magnetic properties, petrophysical maps, igneous rocks, Eastern Carpathians, Calimani massif.

THE METHODOLOGY AND RESULTS OF THE MINING
INVESTIGATIONS BY RADIOMETRIC AND MAGNETIC
SUSCEPTIBILITY MEASUREMENTS

FL. NEACSU, I. MARCOSANU, G. GONCEAR, C. LOSTUN
Enterprise of Geological and Geophysical Surveys, Bucharest

The methodological data regarding the radiometric and magnetic susceptibility measurements "in situ" by mining rocks and the results obtained by investigation of some objectives from North Dobrogea, the Bistritei Mountains, the Metaliferi Mountains, the Poiana Rusca Mountains and the Bihor Mountains are described.
Key words: radiometric measurements,magnetic susceptibility, mining works, methodology, Dobrogea, the Bistritei Mountains, the Metaliferi Mountains, the Poiana Rusca Mountains, the Bihor Mountains.

GEOLOGICAL ELEMENTS IN THE DITRAU MASSIF DEDUCED
FROM THE NATURAL GAMMA-RADIOACTIVITY MEASUREMENTS

N. HEREDEA, T. STRUGARU, FL. NEACSU, GH. TEULEA
Enterprise of Geological and Geophysical Surveys, Bucharest

The paper presents geological interpretation elements coming from the correlation of natural ?-radioactivity data, obtained by field radiometric prospecting, radioactive logging measurements and mining radiometric measurements performed in the area of the Ditrau alkaline massif.
Key words: Ditrau alkaline massif, interpretation, field, radiometric prospecting, radioactive logging, mining radiometric measurements.

NEW ISOTOPIC STUDIES OF THE MINERALIZATIONS ASSOCIATED
TO BANATITIC AND NEOGENE MAGMATISM OF THE APUSENI MOUNTAINS

GH. POP1, I. WEISZ1, GH. POPESCU2, M. SOROIU2
1Enterprise of Rare Metals, Bucharest
2Institute for Physics and Nuclear Engineering, Bucharest

The paper presents the geologo-geophysical interpretations of the new results, obtained through isotopic methods on polymetallic ores. On the basis of the lead isotopic data, one can specify the original source of Pb and establish parallels with the Pb normal isotopic composition from other deposits in the country, with the aim of determining the relative ages. By the K – Ar method, the age of some mineralizing processes is specified.
Key words: isotopic studies, common Pb, absolute age, mineralizing processes, source Pb.

CONTRIBUTIONS OF THE RADIOMETRIC EXPLORATION BY STUDYING
THE DISTRIBUTION OF THE GAMMA FIELD OVER THE GROUND

A. LUNG
Enterprise of Rare Metals, Bucharest

The paper presents the results of various experimental measurements, carried out over the separation line ground/air up to 2 meters high.
The case histories of gamma field distribution are presented; theoretical cases, practical ones as well as several case histories in low anomalous zones. One can use common radiometers, with a NaI 75 cm3 crystal.
The method is supposed to provide good results in the low anomalous zones, which by common working can be overlooked.
Key words: radiometric exploration, low anomalies, gamma field, spatial distribution, attenuation.

CONTRIBUTIONS TO THE WORKING AND DATA PROCESSING METHODS
IN THE FIELD GAMMA-RAY SPECTROMETRY

ELEONORA NICOLAESCU, A. BRATILA
Enterprise of Rare Metals, Bucharest

The paper presents the way of solving the problems the appear when performing the gamma-ray spectrometry workings as well as the possibilities of applying this method for clearing up some geological problems characteristic of the radioactive mienralization.
The methods of mathematically processing field gamma ray spectrometry results are considered.
Key words: gamma-ray spectrometry, energy spectrum, radioactive elements, computational data processing.

POSSIBILITIES OF ALPHA SPECTROMETRY APPLICATION ON THICK
SOURCES USED IN THE INVESTIGATION OF URANIUM MINERALIZATION

G. POP, I. CRISTEA, D. ZAZULEAC
Enterprise of Rare Metals, Bucharest

Alpha spectrometry on thick sources permits the evaluation of some isotopic abundances within the radioactive series. The disturbances outlined in the isotopic ratios, are determined by various physico-chemical processes, such as: uranium leaching, levigation, migration and accumulation.
The direction and intensity of these disturbances represent data which, enclosed in a geological pattern, lead to a selective image of the uranium accumulation and to phenomena that take place in the geological sequence between the source structures and host structures.
Key words: alpha spectrometry on thick sources, leaching, levigation migration, accumulation, geological pattern.

DATA PROCESSING METHODS IN THE EVALUATION
OF THE PROSPECTS FOR RADIOACTIVE MINERALIZATION

GH. GRECEA
Enterprise of Rare Metals, Bucharest

The paper presents programme of processing geological, geophysical and geochemical data with the aim of elaborating prognosis maps concerning the radioactive mineralization.
Key words: data processing, prospect, radioactive mineralization.

A COMPARATIVE STUDY ON THE CONTOURING POSSIBILITIES BY
RADIOMETRIC METHODS OF THE URANIC ANOMALIES
IN THORIC FORMATION AREAS

ST. OSVALD, MILENA OSVALD, I. SERBAN, C. GHEORGHE, LORENA GHEORGHE
Enterprise of Rare Metals, Bucharest

The paper presents the results of the corroborated emanometric and radiometric data in order to separate the uranic zones as well as their development tendencies. The association mood of the radioactivity growth with the uranic nature zones is investigate. By means of reconnaissance pattern techniques, one could determine the spectral composition of the anomalies investigated and the framing of the anomalous zones in groups connected to certain types of radioactive mineralizations.
Key words: gamma-ray spectrometry, energetic lines, emanometry, anomalous areas, radioactive mineralization.

RADIOMETRIC DATA PROCESSING IN THE SURVEY OF THE
GEOLOGICAL STRUCTURES FAVORABLE TO THE ACCUMULATION
OF RADIOACTIVE MIENRALIZATION

I. ZAMFIR, R. ERHAN, N. MAIORESCU, N. PETRESCU, D. POPESCU
Enterprise of Rare Metals, Bucharest

The paper presents methods of separating the useful signals from the background noises when processing the data for the radiometric explorations.
The presence of the geochemical halos, specific to the radioactive mineralizations, imposes the corroboration of the geophysical and geochemical data when interpreting the results; in this respect, the interpretation procedures are analysed.
Key words: radiometric explorations, geochemical halos, radioactive mineralizations, useful signals, background noise.

CONTRIBUTIONS TO THE ENERGY SPECTRUM STUDIES
OF THE GAMMA RAYS IN THE BOUNDARY ZONE
OF A RADIOACTIVE MIENRALIZED LAYER

M. SASARMAN
Enterprise of Rare Metals, Bucharest

Gamma ray spectrometry studies were carried out, on layer models and "in situ" regarding the transformation to which is submitted the measured gamma-ray energy spectrum of the natural radioactive elements in the boundary zone. Measurements were carried out with a portable monochannel spectrometer having 2" x 2" NaI(Tl) monocrystal.
Key words: gamma rays, energy spectrum, mineralized layer, boundary zone, NaI(Tl) monocrystal.

HERCYNIAN MAGMATISM IN THE CIBIN-SIBIEL AREA
OUTLINED BY Rb-Sr METHOD

GH. POP1, I. ENE1, GH. POPESCU2
1Enterprise of Rare Metals, Bucharest
2Institute for Physics and Nuclear Engineering, Bucharest – Magurele

The latest geologo-geophysical investigations pointed out some plagiogranite dikes and gneissic granites of the arteritic type, encountered in the medium and superior basins in the Sibiel valley, especially on its right affluent – the brook Sibielas.
The two types of rocks represent the surface exponents of a large batholith, existent in the region, underlying the metamorphites that belong to the Sebes – Lotru series.
The age of the settling in place of the plagiogranites as well as of the gneissic granites of the arteritic type was established by the Rb-Sr method. This age correlated with the age process of metasomatosis, on restricted spaces, under the influence of a preponderantly alkaline support and of high temperature, permitted the formation of a prospect metallogenetic field.
Key words: Hercynian magmatism, Rb-Sr method, granites.

GEOPHYSICAL STUDY OF VALEA LUI STAN TYPE GOLD MINERALIZATION

D. IOANE, N. SCUPIN, GABRIELA GRABARI
Institute of Geology and Geophysics, Bucharest

Data from geophysical methods applied in the area (magnetometry, electrometry, mercurometry, gamma ray spectrometry, X-ray fluorescence) have shown the contribution of each geophysical method in revealing structural, petrographic and metallogenetic features, chiaracteristic of the Valea lui Stan type gold mineralizations.
Key words: complex geophysical investigation, gold investigations, Southern Carpathians.

DATA BASIS FOR PETROPHYSICS

RODICA ZABLAU, D. CIPOIANU
Institute of Geology and Geophysics, Bucharest

The paper solves the problem of an efficient storage of the complex information in the conditions of memory economy, rapid and confortable access to information and its multiple using.
The generality of the solution allows its utilization in other domain of activity also.
Key words: data basis, information, storage, petrophysics.

VALIDITY OF UPWARD CONTINUATION INTEGRALS
AT VERY HIGH HEIGHTS

M. IVAN
Faculty of Biology, Geology and Geography, University of Bucharest

The exact variations of the magnetic potential and those of the field components are compared with the values obtained using the upward continuation integrals. Due to the finite extent of the observed data, such integrals are improper to obtain accurate magnetic values at great elevations above the datum plane but good results are found in the gravity case.
A complex model illustrates the mathematical assertion.
Key words: upward continuation integrals validity, gravity, magnetics.

THE CORRELATION ANALYSIS OF VERTICAL ELECTRICAL SOUNDINGS

O. SUCIU, T. MOLDOVEANU
Institute of Energetic Studies and Designs, Bucharest

The analysis of a large number of vertical electrical soundings required finding out some quantitative expressions of data correlation. The distance and correlation coefficients proved their utility in the interpretation of VES data.
A programme in FORTRAN language calculates automatically the matrix of distance and correlation coefficients.
Key words: vertical electric soundings (VES), matrix, correlation coefficient.

EARTH PHYSICS AND GEODESY RESEARCHES

Chairman: prof. LIVIU CONSTANTINESCU, corresponding member of the Academy

THE PROCESSING OF REPEATED GRAVIMETRIC MEASUREMENTS
IN THE GRUIU – CALDARUSANI GEODYNAMIC POLIGON

I. CORNEA1, D. GHITAU2, M. N. POPESCU1, I. SOMARDOLEA2,
AL. ILIES2, C. MARCU2
1Centre for Earth Physics and Seismology, Bucharest – Magurele
2Institute of Civil Engineering, Bucharest

High precision gravimetrical measurements with a very modern equipment were performed in the Gruiu – Caldarusani geodynamic polygon. In this paper are shown the field works and data processing of repeat-of measurements. Gravimetrical data will complete the information obtained by high-precision geodetical methods used in detecting the movements of bench-marks from this geodynamic polygon.
Key words: repeated gravimetrical measurements, high-precision geodetical method, bench-marks geodynamic behaviour.

ON EARTH'S CRUST DISPLACEMENT IN THE GRUIU – CALDARUSANI
GEODYNAMIC POLYGON IN THE PERIOD 1980 – 1986

M. N. POPESCU1, D. GHITAU2, I. CORNEA1, C. SAVULESCU2,
V. LAZARESCU3, A. FLESCHIN2, F. RADULESCU1, C. MOLDOVEANU2
1Centre for Earth Physics and Seismology, Bucharest – Magurele
2Institute of Civil Engineering, Bucharest
3University of Bucharest

The paper presents field geodetic methods, data processing and the complex geological and geophysical interpretation of high-precision geodetical measurement results obtained in the period 1980 – 1986. Certain particular Earth's crust surface behaviour were observed in the geodynamic polygon Gruiu – Caldarusani area, especially in connection with seismic events.
Key words: Earth's crust surfaces behaviour, high-precision geodetical measurements, complex geological-geophysical interpretation, field geodetic methods, data processing.

THE GRAVITY VARIATIONS ON GEODYNAMIC POLYGONS
OF THE S.R. OF ROMANIA AND THEIR PRELIMINARY TECTONIC
INTERPRETATION

C. CALOTA1, V. LAZARESCU1, T. MOLDOVEANU2, DOREL ZUGRAVESCU3
1University of Bucharest
2Institute of Hydroelectric Studies and Designs, Bucharest
3Centre for Earth Physics and Seismology, Geodynamic Department, Bucharest

The gravimetric measurements performed before the earthquake of 30 August 1986 and after it on the Nehoiu-Bisca Rozilei Geodynamic Polygon (practically situated in the epicentral zone) and on the Caldarusani – Gruiu Geodynamic Polygon (situated southwardly at a distance greater than 100 km and separated from the epicentral zone by a distance which is comparable with the depth of hypocentres) revealed significant changes in the distribution gravity variations.
The fact that no level changes have occurred on these polygons, apt to explain the measured gravity variation, the shape of the anomalies, as well as the fact that both of the polygons are crossed by depth fractures, suggests that the adjacent compartments are shifted across these fractures.
Key words: geodynamics, geodynamic polygon, gravity variations, Vrancea earthquakes, predictive elements.

HORIZONTAL GRADIENTS OF RECENT CRUSTAL MOVEMENTS IN ROMANIA

M. N. POPESCU1, V. LAZARESCU2, V. MOCANU3, V. NACU1,
O. ENCULESCU4
1Centre for Earth Physics and Seismology, Bucharest – Magurele
2University of Bucharest
3Enterprise of Geological and Geophysical Prospecting, Bucharest
4Bolintin Petroleum Exploitation, Titu Oil Field

The recently drafted map of horizontal gradients for the vertical component of crustal movements is able to contribute to detecting deep tectonic lineaments (fractures or flexures).
Special interest is displayed by high-intensive gradient sectors and by transitional zones between highly intensive and quiet areas found in Romania.
Key words: Horizontal Gradient Map, Recent Crustal Movements, Deep Tectonic Lineaments.

GROUND POINTS POSITIONING AND GRAVITATIONAL FIELD
EARTH CHARACTERISTICS DETERMINATION BY ORBITAL
AND INERTIAL METHODS

I. RADU, I. SERBAN, MONICA ROTARU
Military Topographic Direction, Bucharest

After a present-stage analysis of the orbital and inertial methods a solving problem variant is presented.
Key words: Dynamic Satellite Geodesy, inertial platform, gravitational field, orbital methods, inertial methods, zonal and tesseral harmonics, motion parameters.

CONTRIBUTIONS FOR THE DETERMINATION
OF THE GEODETIC NETWORKS

M. SAMUILA
Institute of Researches and Design for the Water Management, Bucharest

The actual design of free networks for the processing of incorrect data (measured elements and point coordinates) although qualitatively superior to the conventional one, has certain theoretical and practical disadvantages, viz. the results depend on the selection of arbitrary points and extensive calculations are required. On the basis of theoretical investigations, the author suggests practical, advantageous solutions.
Beside the theoretical approach, the paper also present applications to current geodetic networks.
Key words: Geodesy, national geodetic networks, special technical-engineering geodetic networks, measurement processing.

SCALING RELATIONSHIPS FOR THE NEAR-FIELD GROUND MOTION

C. I. TRIFU, M. RADULIAN
Centre for Earth Physics and Seismology, Bucharest, Magurele

A set of monomial scaling relations to parametrize several measures of strong motion (peak velocity, peak starting-phase acceleration, peak stopping acceleration) is proposed. Dynamic solutions are obtained for a 2D (P, SV and SH) stress drop of faulting, and computed ground motion is used to calibrate the scaling relations. The numerical method is reliable within its frequency range of validity, which is 0 to 5 – 6 Hz for the chosen grid steps.
Key words: Strong motions, stress-drop model, kinematic parameters.

A LARGE SEISMIC SEQUENCE ON APRIL 27 – 29, 1986
IN THE CARPATHIAN FOREDEEP

M. C. ONCESCU, C.-I. TRIFU
Centre for Earth Physics and Seismology, Bucharest, Magurele

Relocation of 60 earthquakes showed that their epicenters were inside an area of 15 x 8 squared km, oriented SW – NE, with depths between 15 and 28 km. a foreshock of ML = 3.0 preceded with 21 s the main shock of ML = 5.0. Their fault plane solutions and the aftershocks composite mechanism solutions suggested that the energy was released on the Precarpathian Fault, which strikes SW – NE and dips 70° towards NW in the region. Other faults were activated too. The main shock had M0 ) 5 x 10 dyne x cm, = 36 bar, r = 0.44 km, u = 5 cm.
Key words: Vrancea foredeep, earthquake sequence, precarpathian Fault.

DEPTH DISTRIBUTION OF STRESS BARRIERS IN VRANCEA REGION

C.I. TRIFU
Centre for Earth Physics and Seismology, Bucharest, Magurele

Corrected displacement amplitude spectra of weak and moderate ML = 2.5 – 5.0 Vrancea Earthquakes (H = 0 – 201 km) exhibit an obvious shape with two corner frequences and two slopes. This behaviour is related to fractional tress drop, due to local small- and moderate-scale barriers, and its value lies between 20 and 40% of the effective stress. Depth distribution of stress barriers within the region is found to be heterogeneous.
Key words: Vrancea region, fractional stress drop, stress barriers.

ON THE STRESS TENSOR IN VRANCEA REGION
AN MOESIAN PLATFORM

M. C. ONCESCU
Centre for Earth Physics and Seismology, Bucharest, Magurele

The deviation stress tensor was determined starting from the principal strain directions (P and T axes from fault-plane solutions). Let be the principal stresses. For the Moesian Platform, (bi-axial stress) and the azimuths and dips are ; more interesting for Vrancea region (75 km < h < 200 km), and , which means that pressures act horizontally in a NE – SW direction and tensions vertically. The actual fault planes were also identified.
Key words: stress tensor, Vrancea region, Moesian Platform.

DEPTH VARIATION OF SEISMIC-MOMENT TENSOR AXES
IN VRANCEA SEISMIC REGION

M. C. ONCESCU, C.-I. TRIFU
Centre for Earth Physics and Seismology, Bucharest, Magurele

Fault plane solutions of 114 intermediate depth events with ML = 2.6 – 5.0 are determined by a relative moment tensor inversion using both long period levels of displacement spectra of direct P and SV wave trains and the corresponding time domain first motion signs. Vertical tension and horizontal compression axes were found and the diversity in mechanisms is explained by local heterogeneities in stress. A biaxial stress is required except in the 105 – 120 km depth interval.
Key words: Vrancea region, moment tensor inversion, local mechanism.

THE AUGUST 30, 1986 VRANCEA EARTHQUAKE:
FAULT GEOMETRY AND AFTERSHOCK FOCAL MECHANISM

C.-I. TRIFU, M. C. ONCESCU
Centre for Earth Physics and Seismology, Bucharest, Magurele

A number of 77 aftershocks with 120 km < h < 160 km were relocated with the Joint Hypocenter Determination technique. Their refined hypocenters lie on a NNW dipping plane, permitting an unambiguous discrimination between the two nodal planes. The fault area has 29 km in a WSW – ENE direction and dips 25 km oblique downward between 131 and 148 km depth totalizing 725 squared km. Composite fault plane solutions of aftershocks were also determined.
Key words: Vrancea region, JHD method, fault area.

INVESTIGATION OF THE MOESIAN PLATFORM'S DEEP
STRUCTURE BY ELECTROMAGNETIC INDUCTION METHODS

D. STANICA, MARIA STANICA
Institute of Geology and Geophysics, Bucharest

In this paper the deep magnetotelluric sounding curves and the maps of low frequency telluric field carried out on the Moesian Platform area are examined. The results provide information on the thickness of the sedimentary cover as well as on the astenospheric zone of partial melting. The conductivity of this zone reaches several thousands of Siemens in the central part of the investigated area.
Key words: magnetotelluric sounding, telluric field, Moesian Platform, conductivity, astemospheric zone.

THE MAGNETIC CONTROL NETWORK OF ROMANIA

L. BESUTIU, GEORGETA BESUTIU
Institute of Geology and Geophysics, Bucharest

To enable finalization of the ground magnetic map of Romania a special magnetic control network has been performed.
It consists of 38 first order stations regularly spaced on the territory, linked by 91 ties constituting 54 triangles.
The annual means of the geomagnetic elements Z, T and H, centered at the epoch 1984.0 are provided.
Key words: geomagnetism, control network, Romania.

PROSPECTS AND LIMITATIONS IN USING THE GEOMAGNETIC
TRANSIENT FIELD SOURCES TO INVESTIGATING
THE EARTH INNER STRUCTURE

A. SOARE
Institute of Geology and Geophysics, Bucharest

The development of the Earth's inner structure investigation by inductive electromagnetic methods depends on the recording system and the experimental data processing improvement.
It is outlined that this development must be correlated with a better knowledge of the transient field sources.

THE HOMOLOGATE OF THE CONTINUOUS GEOMAGNETICAL
RECORDING FROM THE DREPTU-POIANA TEIULUI STATION

A. SOARE, D. ALEXANDRESCU, MIOARA ALEXANDRESCU
Institute of Geology and Geophysics, Bucharest

A new station of permanent recording of the geomagnetic field situated in Romania's North – East zone and put into current function in 1985, is presented.
The recordings made at this station are compared with those made at the Surlari Geophysical Observatory, underlining the peculiarities pointed out.
Key words: geomagnetic field permanent recording.

THE ESTABLISHING OF CERTAIN SOLUTIONS ON THE
RESEARCHING OF THE DEEP STRUCTURES THROUGH
ELECTROMAGNETIC METHODS

A. SOARE, GH. IONESCU, MIOARA ALEXANDRESCU
Institute of Geology and Geophysics, Bucharest

The utilization of some heterogeneous field sources, the recording errors and inadequate processing methods determine difficulties in the quantitative interpretation of depth geomagnetic soundings.
Some ideas related to the possibility of improving the method of processing data are presented by an adjustment of a more corresponding model.
Key words: field sources, depth geomagnetic sounding, solution stabilization.

A COMPUTING REGRESSION PROGRAM TO DETERMINING
THE DIURNAL-VARIATION CORRECTION IN AEROMAGNETICS

F. SCURTU
Institute of Geology and Geophysics, Bucharest

One of the corrections needed in aeromagnetics is the removal of temporal variations from the recorded data. Several authors have shown that the diurnal variation recorded at a fixed terrestrial station is sometimes not acceptable to correct the data acquired in an aircraft at several tens or hundreds of kilometers, because important shiftings and amplitude differences were detected in the geomagnetic time variations at observatories at several tens of kilometers of each other.
A trigonometric regression was found to be an efficient method to determine analytically the diurnal variation to be removed from the recorded data. Examples have shown a very good agreement between actual and computed curves of the diurnal variation.
Key words: mathematical regression, diurnal variation, aeromagnetics, computer.

THE MAGNETIZATION BY PHASE TRANSITION, A MAIN MECHANISM
OF THE RESIDUAL MAGNETIZATION OF ROCKS

D. CONSTANTINESCU
Institute of Geology and Geophysics, Bucharest

Deciphering the closeness of residual rock magnetization process points out the special part of the very small sized granules. The paper analyzes the critical dimension dependence upon temperature and pressure and also the implications of this dependence in case of magnetic phase transition. The importance of the Koenisberger coefficient, the part of the speed-governing elements and the consequences of the change of the critical dimension as a result of temperature and pressure variations are affirmed.
Key words: magnetization, critical dimension, temperature, pressure, phase transition.

HYPOTHESIS CONCERNING A POSSIBLE CONNECTION BETWEEN
HYDROTHERMAL ACTIVITY AND THE CHANGE
OF THE GEOMAGNETIC FIELD POLARITY

D. CONSTANTINESCU
Institute of Geology and Geophysics, Bucharest

The paper is based on observation of certain parallelisms between some magmato-tectonic and hydrothermal events succession and the one based on the residual magnetization of rocks. The hypothesis is advanced of a possible causal connection between the respective successions hypothesis with implications on delimiting areas of economic inerest on the basis of the magnetometrical data.
Key words: geomagnetism, hydrothermalism, tectonics, magnetism, magnetization.

INDUCTION MODEL FOR THE SECULAR VARIATION
OF THE GEOMAGNETIC FIELD IN EUROPE

C. DEMETRESCU1, MARIA ANDREESCU1, T. NESTIANU2
1Centre for Earth Physics and Seismology, Bucharest, Magurele
2 Institute of Geology and Geophysics, Bucharest

The solar-cycle related variation in the annual means of the horizontal component of the geomagnetic field between 1952 and 1980 at European observatories is discussed in terms of magnetic and electromagnetic induction by the external dipole. The lateral variation of magnetic properties of the lithosphere in Europe was derived and discussed in terms of tectonic structure.
Key words: secular variation, magnetic induction, Europe, magnetic properties, lithosphere.

CONTRIBUTIONS TO THE SPECIFICATION OF THE EAST CARPATHIANS
GEOTECTONIC MODEL

M. VISARION, M. SANDULESCU, D. STANICA, LIGIA ATANASIU
Institute of Geology and Geophysics, Bucharest

The paper presents an improved geotectonic model of the East Carpathians inferred from the quantitative analysis of the gravity anomaly according to magnetotelluric, geomagnetic and seismotectonic data related to the deep drilling geological data. The results are illustrated by characteristic sections which include the configuration and total thickness (7 – 8 km) of the flysch nappes, a major graben of the underthrust platform formations and the crust thickening (42 – 46 km) between the Siret crust fault and its consumption paleoplane.
Key words: geomagnetic and magnetotelluric sounding, crust consumption plane, underthrust platform, crust discontinuities.

A GEOTHERMAL STUDY OF THE GETIC DEPRESSION
BETWEEN THE OLT AND GILORT RIVERS

S. VELICU1, A. NEGUT2, ADRIANA ZAMFIR1
1 Institute of Geology and Geophysics, Bucharest
2Faculty of Biology, Geology and Geography, the University of Bucharest

The geothermal gradient distribution on the outcropping area of the Mesozoic and Paleogene formations in the Getic Depression is discussed. Some explanations regarding the origin of thermal water occurences from Cozia – Caciulata – Calimanesti, Olanesti and Govora are presented.
Key words: geothermal gradient, thermal waters, Getic Depression.

ON THE GEOLOGICAL AND THERMAL EVOLUTION
OF THE PANNONIAN DEPRESSION

C. DEMETRESCU, GABRIELA POLONIC
Centre for Earth Physics and Seismology, Bucharest, Magurele

The geological and thermal evolution of the Romanian part of the Pannonian Depression is discussed, based on bore-hole and heat-flow data. A backstripping technique with decompaction is used to reconstruct the spatial and temporal distribution on tectonic subsidence and heat flow. The results are interpreted in terms of lithospheric stretching models for the evolution of sedimentary basins.
Key words: Pannonian Depression, heat flow, tectonic subsidence, lithosphere stretching.

HYDROCARBON SOURCE ROCKS IN THE PANNONIAN
DEPRESSION – GEOTHERMAL MODEL

C. DEMETRESCU1, GABRIELA POLONIC1, N. BALTES2
1Centre for Earth Physics and Seismology, Bucharest, Magurele
2Oil and Gas Research and Design Institute, Research Section Group, Bucharest

A model of the thermal and subsidence history of Neogene sedimentary formations of the Pannonian Depression is presented, based on heat-flow and bore-hole data. The level of thermal maturation of kerogene of these formations is evaluated by an integrated time/temperature/depth analysis and the distribution of areas of possible hydrocarbon generation is presented. The model is checked against geochemical and microscopy data as obtained on cores.
Key words: Pannonian Depression, thermal history, hydrocarbon generation

PRECURSORY SEISMICITY PATTERNS RELATED TO THE 30th AUGUST 1986
VRANCEA SUBCRUSTAL EARTHQUAKE

V. MARZA1, V. BURLCU1, A. PANTEA1, ZINA MALITA1,
GR. ARSENE2, GEORGETA MIHALACHE2, A. DUMITRASCU2
1Centre for Earth Physics and Seismology, Bucharest, Magurele
2INCREST, Bucharest

A large range of seismic precursory phenomena belonging to all temporal stages of (geo)physical preparatory process are presented, viz. (i) occurrence regularity/ciclicity (ii) (pre)seismic quiescence, (iii) hypocentral migration/progression, (iv) magnitude-frrequency b-value, (v) anomalous crustal activity, (vi) foreshocks, etc., mostly 'a priori' detected and reported.
The involved premonitory information is analysed and interpreted in the framework of Vrancea (subcrustal) earthquake prediction.
Key words: Vrancea region, 30 August 1986 earthquake, precursory seismicity patterns, earthquake prediction.

THE SIHLEA CRUSTAL SEISMIC SEQUENCE
(APRIL – AUGUST 1986) A POSSIBLE 'HOT SPOT'
IN THE VRANCEA REGION

V. MARZA, V. BURLACU, ZINA MALITA, A. PANTEA
Centre for Earth Physics and Seismology, Bucharest, Magurele

The Vrancea crustal sequence (145 events) during 27th April – 27th august 1986 of average coordinates 45.5 N and 27.1 E is integrated in the framework of precursory seismicity allied to the 30th August 1986 Vrancea subcrustal earthquake through analysis of composition, temporal stages, source parameters, sequence statistics as well as causal connection with the preparatory process of the 1986 major earthquake. The significance of this sequence – in the context of earthquake prediction – is discussed by means of its relation to a 'hot spot'.
Key words: Vrancea region, crustal seismic sequence, hot spot.

20th CENTURY'S VRANCEA MAJOR EARTHQUAKES:
A COMAPRATIVE VIEW

V. BURLACU, V. MARZA, A. PANTEA
Centre for Earth Physics and Seismology, Bucharest, Magurele

The three Vrancea subcrustal major earthquakes during the present century, namely: 1940 November 10 (Ms = 7.4), 177 March 04 (Ms = 7.2) and 1986 August 30 (Ms = 7.0) are discussed by means of a comparative analysis of source parameters, macroseismic effects as well as precursory phenomena, both similarities and dissimilarities being emphasized.
Key words: Vrancea seismic region, subcrustal major earthquakes, comparative analysis.

DYNAMIC CHARACTERISTICS OF THE QUARRY BLAST
INDUCED GROUP MOTION

A. PANTEA, V. BURLACU, V. MARZA
Centre for Earth Physics and Seismology, Bucharest, Magurele

The main dynamic parameters (displacement, velocity, frequency / period) of the seismic waves originating from quarry blasts in the near field at the Cernavoda NPP site as well as their relationships with the principal blast parameters (yield, distance) are analysed.
Key words: dynamic parameters, quarry blasts, propagation formula.

THE ATMOSPHERIC OZONE FOR 1986 IN BUCHAREST

M. FRIMESCU, LAURA MANEA
Institute of Meteorology and Hydrology, Bucharest

Based upon daily total ozone measurements, the monthly and seasonal means for 1986 in Bucharest are presented. As against the natural ozone variation the anthropic influence traced in May is emphasized and its effects in time are delimited.
Key words: total ozone, natural ozone variation, anthropic influence.

ON THE POSSIBILITY OF EXISTENCE OF SOME
CORRELATIONS BETWEEN STRONG EARTHQUAKES (M > 7.5)
OCCURRENCE AND THE SOLAR ACTIVITY

V. A. BULGAREANU, M. BARBU, E. CRISTESCU, C. COSTACHE
Enterprise of Geological and Geophysical Surveys, Bucharest

In this note, an attempt is made to establish the presence of some relationships between the world strong (M > 7.5) earthquakes occurrence in the time spans 1970 – 74 and 1978 – 1985, and some heliogeophysical parameters (Wolf number, solar radio flux, solar flare index, planetary geomagnetic index and the cosmic ray neutron flux intensity).
Key words: strong earthquake, solar activity, heliogeophysical parameters, Wolf number, solar radio flux, solar flare index, planetary geomagnetic index, cosmic rays.

THE SUBSIDENCE OF TRANSYLVANIA'S BASIN:
A POSSIBLE MODEL

C. CRANGANU
Al. I. Cuza University, Faculty of Biology, Geography, Geology, Department of
Geology and Geophysics Engineering, Iasi

A hypothesis for the formation of Transylvania's Basin by subsidence is discussed. Generally speaking two mechanisms may be assumed: the stretching of the lithosphere and the heating – cooling of the same. But some secondary mechanism may also be involved in the appearance of Transylvania's Basin (e.g. diapirism, faulting, etc.).
In the first part some previous models are presented and in the second part particular aspects of the Transylvania Basin subsidence model are discussed.
Finally some remarks on the possible errors which can be made concerning the subsidence of the Transylvania Basin are made.
Key words: subsidence, stretching model, heat-cooling model, Transylvania Basin.

THE ROMANIAN TELEMETERED SEISMIC NETWORK:
DATA BASE AND RESEARCH

I. CORNEA, M. C. ONCESCU, C. I. TRIFU
Centre for Earth Physics and Seismology, Bucharest, Magurele

In six years of operation, the Romanian telemetered seismic network provided a large high quality data base, high accuracy arrival times and digital waveforms, which permitted detailed investigations on 3D velocity structure, frequency-dependent quality factors, focal mechanism and source parameters of weak and moderate events. Further development of this network will consist in the increase of dynamic range and installation of horizontal components.
Key words: seismic network, data base, data processing.

THE ANALYSIS OF THE TEMPORAL VARIATION OF THE
CODA ENVELOPE SHAPE FOR VRANCEA INTERMEDIATE EARTHQUAKES

VICTORIA OANCEA, OLIVIA BAZACLIU
Centre for Earth Physics and Seismology, Bucharest, Magurele

The temporal variation of the coda envelope shape for the intermediate earthquakes occurred in Vrancea region in the period September 1981 – December 1985 is studied. Parameters characterizing the deviation of the individual envelope shape from the mean envelope determined for a normal period are analyzed. The anomalous behaviour of these parameters is correlated with the appearance of strong earthquakes in the studied region.
Key words: Vrancea region, intermediate earthquakes, coda envelope, prediction.

DETERMINATION OF TESSRAL HARMONIC COEFFICIENTS
OF THE GEOPOTENTIAL FROM OBSERVATIONS
OF ARTIFICIAL SATELLITES

H. ALEXANDRESCU
Astronomic Observatory of Bucharest City

The dynamic method to obtain the tesseral harmonic coefficients of the geopotential by the satellite orbits and station coordinates differential improvement process is described.
The results are used to obtain the free-air gravity anomalies, viz., the geoid undulation, the deflection of the vertical and the scale correction, implicitly to obtain the Earth's shape.
Key words: spatial geodesy, dynamic method, tesseral harmonic coefficients, differential improvement process, free-air gravitational anomaly, geoid undulation, scale correction.

CORRELATION BETWEEN THE EARTH TIDE AND THE OCCURRENCE
MOMENTS OF VRANCEA EARTHQUAKES AS A POSSIBLE ELEMENT OF
DISCRIMINATION BETWEEN THE HYPOTHESIS EXPLAINING THEIR
MECHANISM

DOREL ZUGRAVESCU1, ILEANA FATULESCU1, RAUL DOROBANTU1,
LIVIU CONSTANTINESCU2, DUMITRU ENESCU1
1Centre for Earth Physics and Seismology, Bucharest, Magurele
2Romanian National Committee of Geodesy and Geophysics, Bucharest

Taking into account the correlation existing between the Earth tide (maximum, minimum, inflexion points) and Vancea earthquakes (occurrence moment and focal mechanism), the authors consider that, by a careful analysis of the spatial distribution of the hypocentres of the earthquakes having several types of mechanisms, a discrimination between hypotheses trying to explain the focal mechanism of intermediate Vrancea earthquakes is possible.
Key words: Earth tides, earthquakes, focal mechanism, Vrancea

CONTRIBUTIONS TO THE KNOWLEDGE OF THE
LITHOSPHERE STRUCTURE IN ROMANIA ON THE BASIS OF SEISMIC DATA

D. ENESCU
Centre for Earth Physics and Seismology, Bucharest, Magurele

Seismic data supplied by 98 large industrial blasts, recorded by 24 seismic stations have allowed the estimation of average P and S wave velocities through principal lithospherical layers in Romania as well as the determination of average thickness of these layers.
For the estimation of lithosphere thickness (values ranging between 50 – 60 km to 180 – 200 km) data supplied by earthquakes have been used too.
Key words: subcrustal lithosphere, Mohorovicic discontinuity, quarry blast, astenosphere low velocity layer.

QUASICONTINUOUS VARIATION LAWS OF THE P AND S
SEISMIC WAVE VELOCITIES IN THE EARTH CRUST IN ROMANIA

D. ENESCU, A. BALA, A. POMPLIAN
Centre for Earth Physics and Seismology, Bucharest, Magurele

Taking into account the hypothesis of the continuous depth variation of the seismic wave velocities, the observational data supplied by 98 large industrial blasts have allowed to apply the Wiechert-Herglotz-Bateman method for determining the variation laws of the P and S seismic wave velocities in the earth crust in Romania. Variation laws of the average velocities have been determined, too.
Key words: industrial blast, quasicontinuous variation law, earth crust, seismic wave velocity, average velocity.

THERMOSTATIC DEVICE FOR CHAMBERS DESTINED TO
TESTING RECORDING APPARATUS OF GEODYNAMICS

RAUL DOROBANTU, DOREL ZUGRAVESCU, ILEANA FATULESCU
Centre for Earth Physics and Seismology, Bucharest, Magurele

The block and its details in the electric schemes are presented. The thermostatic device is provided with the final power stages to switch the heating source and with a digital pointer of the temperature measured in the chamber.
The device assures the thermoregulation in the range of the temperature changes of at most ± 0.05°C, as a function of the thermoinsulating properties of the measurement chamber.
Key words: geodynamics, apparatus of geodynamics, thermoregulation, temperature measurement.

A LONG PERIOD SIGNAL GENERATOR
FOR TESTING GEODYNAMIC APPARATUS

RAUL DOROBANTU, DOREL ZUGRAVESCU, ILEANA FATULESCU
Centre for Earth Physics and Seismology, Bucharest, Magurele

The presentation of the materialized generator is accompanied by a block scheme and the electric schemes.
The generator is provided with the adjustment in steps of the period (10 – 3600 s), of the amplitude (1mV – 5V) as well as of the bias (0 – ±5 V) having a good time stability of the frequency and amplitude and a distortion factor of 1% for the entire frequence range.
Key words: geodynamics, apparatus of geodynamics, long period signal, calibration, signal generator.