Numbers 1, 2, 3, 4

Number 1

GEOPHYSICAL EVIDENCES OF CRUSTAL ANCIENT JUNCTION IN DESAGUADERO-BERMEJO MEGAFAULT (SAN JUAN-LA RIOJA PROVINCE, ARGENTINA)

Acta Geod. Geoph. Hung., Vol. 36(1), pp. 1-16 (2001)

F Ruiz¹ and A Introcaso²

¹CONICET and Facultad de Ciencias Exactas, Fˇsicas y Naturales
Universidad Nacional de San Juan, Meglioli
1160 (sur)-Rivadavia, (C. P. 5400) San Juan, Argentina,
e-mail: fruiz@unsj.edu.ar
²Facultad de Ciencias Exactas, Ingeniería y Agrimensura
Universidad Nacional de Rosario, Instituto de Física de Rosario (CONICET)
Av. Pellegrini 250, (2000) Rosario, Argentina

e-mail: geofisic@fceia.unr.edu.ar

[Manuscript received August 2, 1999, revised September 25, 2000]

A regional study based on the analysis of gravity and magnetic data observed on Sierra de Valle Fértil, Ischigualasto-Villa Unión basin and near areas was carried out.

From different methods of filtering we have obtained a significant gravity anomaly (more than 40 mGal) connected to the tectonic Valle Fértil-La Huerta lineament. Our prediction has located dense masses in middle crust explaining the high gravity.

The big horizontal gravimetric gradient ascending eastwards and its extent towards SSE indicates the meeting of two different crustal slabs in the regional Valle Fértil fault.

From gravity inversion models were calculated. They indicate crustal thinning beneath Ischigualasto-Villa Unión basin located at east of Sierra de Valle Fértil. Besides, the models indicate the deep detach area that allows the rise of the east block and the Valle Fértil range foundation.

From the analysis of regional magnetic anomalies consistent with gravity data, we have pointed out that regional Valle Fértil fault divides two crustal slabs with different magnetization.

On the other hand, in Andean belt and Precordillera, isostasy is made in Airy's isostatic model, while on Pampean ranges it corresponds to regional (Flexural) isostatic model.

Finally, the comparative analysis of these results allows to distinguish two different crusts, both amalgamated along Valle Fértil fault.

Keywords: crustal model; gravity-magnetic results; isostasy; paleosubduction

INTERNAL RELIABILITY OF CROSS-CORRELATED GPS OBSERVATIONS

Acta Geod. Geoph. Hung., Vol. 36(1), pp. 17-29 (2001)

K de Jong

Department of Mathematical Geodesy and Positioning
Delft University of Technology
Thijsseweg 11, 2629 JA Delft, The Netherlands
e-mail: k.dejong@geo.tudelft.nl

[Manuscript received September 7, 1999]

In this contribution analytic expressions are derived for the Minimal Detectable Biases (MDBs) of dual-frequency cross-correlated GPS code and carrier observations. This is done for three different short baseline models. Short in this respect means that orbital and atmospheric biases are assumed absent. The stochastic model of the observations, used in the derivations, is very general and allows for using different variances of the observations of the same satellites and correlation between them. It is also possible to assign satellite specific weights to each of the satellites tracked. Finally, the cross-correlating MDBs are compared to their non-cross-correlating counterparts.

Keywords: cross-correlation; GPS; reliability

ON THE COMPARISON OF DIFFERENT APPROACHES TO ATMOSPHERIC EFFECTS IN THE THEORY OF NUTATIONS AND PRECESSION
(A REMARK)

Acta Geod. Geoph. Hung., Vol. 36(1), pp. 31-34 (2001)

S M Molodensky¹ and E Groten²

¹Institute of the Physics of the Earth
Bolshaja Gruzinskaja, 10, RU--123810 Moscow, Russia
²Institute of the Physical Geodesy
Petersenstraße 13, D-64287 Darmstadt, Germany

[Manuscript received March 1, 2000]

The influence of atmospheric tides on the Earth's nutation may be estimated by two different methods: 1. by using empirical data about the distributions of the pressure variations and (or) the winds in the atmosphere and 2. by means of numerical integration of Laplace tidal equation in the atmosphere. The first way was used in (Dehant et al. 1996, Hinderer et al. 1996); the second one in (Molodensky and Groten 1997). Below we'll try to show that, in spite of some undoubtful advantages of the first approach (the errors of numerical integration of complicated and even not totally known dynamical equations in the atmosphere are excluded), it has also some deficiencies which become apparent in the estimation of the pressure perturbations for precession.

Keywords: atmospheric tides; Earth's nutation; Earth's precession

ROBUST ALGORITHMS FOR RELATIVE ORIENTATION

Acta Geod. Geoph. Hung., Vol. 36(1), pp. 35-38 (2001)

L Battha and J Somogyi

Geodetic and Geophysical Research Institute
of the Hungarian Academy of Sciences
H-9401 Sopron, POB 5, Hungary

[Manuscript received June 21, 2000]

Relative orientation is an important procedure to obtain three-dimensional, accurate informations from stereo images. During this procedure, the pictures are rotated in such a way that a 3D model can be constructed. With the help of the rotation parameters it is easy to create normal-case images, and the stereomodel formed by them can be correlated by one dimensional correlation. When more than five points are involved, it is generally accepted to use the least-squares method, since it is assumed that the observation errors follow normal distribution. It is known from computational experiences that the presence of outliers in data sets could lead to unacceptable results if the least-square method is used. To eliminate such uncertainties, robust estimation methods should be used instead. This paper describes robust solutions, using the L₁-norm and the Cauchy-function, for the relative orientation of stereo-pairs; numerical examples are also given.

Keywords: Cauchy-function; L₁-norm; relative orientation; robust estimation

PARENT DISTRIBUTION TYPE-DOMAIN OF THE APPLICABILITY OF THE SAMPLE STANDARD DEVIATION TO CHARACTERIZE THE DISPERSION OF THE DATA IN A SAMPLE

Acta Geod. Geoph. Hung., Vol. 36(1), pp. 39-54 (2001)

F Steiner¹ and B Hajagos²

¹Geophysical Department, University of Miskolc
H--3515 Miskolc, Egyetemváros, Hungary
²Institute of Mathematics, University of Miskolc
H--3515 Miskolc, Egyetemváros, Hungary

[Manuscript received July 21, 2000]

The paper characterizes the error of the sample standard deviation (\sigma_emp,corr or s.s.d.) by the "scatter of scatter" (\sigma_\sigma), on one hand, and on the other hand, by the semi-intersextile range of the \sigma_emp,corr-estimates, denoted by Q_{\sigma, n}. It is advantageous to "norm" by Q_{\sigma, 4} and therefore the quotient Q_{\sigma, n}/Q_{\sigma, 4} is the abscissa on the Figs 4, 5, 6 and 7. (It is perhaps not superfluous to mention that n=4 can be regarded as minimum sample size which is able to give an also practically real estimate for the theoretical value of the scatter \sigma.)

Similarly as by the investigation of the arithmetic means, it turned out also for the sample standard deviations that the law of large numbers can be fulfilled even if the corresponding asymptotic scatter is infinite, and in addition (in a small type-domain) also when the theoretical value \sigma does not any more exist.

Keywords: asymptotic scatter; law of large numbers; standard deviation; scatter; semi-intersextile range

MULTISCALE SIGNAL-TO-NOISE THRESHOLDING

Acta Geod. Geoph. Hung., Vol. 36(1), pp. 55-86 (2001)

W Freeden, V Michel, M Stenger

University of Kaiserslautern
Geomathematics Group
67653 Kaiserslautern, POB 3049, Germany,
e-mail: freeden@mathematik.uni-kl.de

[Manuscript received August 18, 2000]

The basic idea behind selective multiscale reconstruction of functions from error-affected data is outlined on the sphere. The selective reconstruction mechanism is based on the premise that multiscale approximation can be well-represented in terms of only a relatively small number of expansion coefficients at various resolution levels. An attempt is made within a tree algorithm (pyramid scheme) to remove the noise component from each scale coefficient using a priori statistical information (provided by an error covariance kernel of a Gaussian, stationary stochastic model).

Keywords: multiscale reconstruction of functions; noise; physical geodesy; spherical wavelet theory

AN ESTIMATION OF DIFFERENTIAL ATTENUATION BENEATH THE GAURIBIDANUR SEISMIC ARRAY IN SOUTHERN INDIA

Acta Geod. Geoph. Hung., Vol. 36(1), pp. 87-96 (2001)

J N Tripathi

Department of Earth and Planetary Sciences
University of Allahabad
Allahabad--211 002, India

[Manuscript received December 12, 1999]

The differential attenuation beneath the Gauribidanur seismic array has been estimated using the spectral ratio method. Deep focus earthquakes originating in the Hindukus region have been considered for this study. In fact, the estimated Q is the combined effect of the intrinsic attenuation and the attenuation due to scattering. The estimated standard deviation and mean of the differential attenuation have been found as 0.18 s and --0.06 s for the array, respectively. The Q_GBA is estimated to be 25. It is significant enough and may be due to the scattering by the inhomogeneities beneath the array.

Keywords: attenuation; seismic array; scattering; spectral ratio method

ISOSEISMAL MAP AND TECTONICAL POSITION OF THE KOMÁROM EARTHQUAKE OF 1763

Acta Geod. Geoph. Hung., Vol. 36(1), pp. 97-108 (2001)

P Varga¹, Gy Szeidovitz¹, R Gutdeutsch²

¹Geodetic and Geophysical Research
Institute of the Hungarian Academy of Sicences
H--1112 Budapest, Meredek u. 18, Hungary
²Institut für Meteorologie und Geophysik
Universität Wien
A--1090 Wien, Althan str. 14, UZA II, Austria

[Manuscript received May 17, 2000]

The seismicity of the Pannonian Basin is not yet understood. To improve our knowledge in this field the geological position as well as the damages caused by the biggest known earthquake of the inner part of the Pannonian Basin, i.e. the Kom rom earthquake of 1763 was investigated. It is shown that this earthquake had probably an epicentral intensity of 9.5 MSK, and its origin was in connection with the Rába-Hurbanovo tectonic line.

Keywords: intraplate earthquakes; isoseismal lines; Rába-Hurbanovo line; taxpayer losses

POST-NEWTONIAN CORRECTIONS IN THE DYNAMICS IN THE EARTH-MOON SYSTEM AND THEIR IMPORTANCE FOR THE RELATIVISTIC THEORIES OF GRAVITATION
(A HISTORICAL CASE STUDY)

Acta Geod. Geoph. Hung., Vol. 36(1), pp. 109-117 (2001)

W Schröder¹ and H-J Treder²

¹Hechelstrasse 8, D-28777 Bremen Roennebeck, Germany
²Rosa-Luxemburg-Strasse 17a, D-14282 Potsdam, Germany

[Manuscript received April 22, 1999]

As an example of a historical case study, some aspects of the post-Newtonian corrections in the Earth-Moon dynamics are described and discussed.

Keywords: Earth dynamics; Earth-Moon distance; non-Newtonian gravitational theory; relativistic theories of gravitation

KEPLER AND GRAVITATION

Acta Geod. Geoph. Hung., Vol. 36(1), pp. 119-121 (2001)

W Schröder¹ and H-J Treder²

¹Hechelstrasse 8, D-28777 Bremen Roennebeck, Germany
²Rosa-Luxemburg-Strasse 17a, D-14282 Potsdam, Germany

[Manuscript received April 22, 1999]

Some aspects of Kepler's contribution to the explanation of the law of gravitation are discussed with a historical background. The transition from Keplerian to Newtonian ideas is explained.

Keywords: gravitation; Kepler; Newton

Book reviews

Acta Geod. Geoph. Hung., Vol. 36(1), pp. 123-124 (2001)

M PÉCSI ed. in chief: Landform Evolution Studies in Hungary. Akadémiai Kiadó, Budapest, 1999. 216 pp + 18

A Ádám

Acta Geod. Geoph. Hung., Vol. 36(1), pp. 124-124 (2001)

W SCHRÖDER ed.: Wege zur Wissenschaft -- Gelehrte erzählen aus ihrem Leben / Pathways to Science - Scientists tell of their life and work

J Ver\otilde;

Number 2

GEOMAGNETIC ACTIVITY AND RADIO WAVE ABSORPTION IN THE EQUATORIAL REGION

Acta Geod. Geoph. Hung., Vol. 36(2), pp. 125-131 (2001)

V U Chukwuma

Department of Physics, Ogun State University
Ago-Iwoye, Nigeria
e-mail: victorchukwuma@yahoo.com

[Manuscript received October 6, 2000]

Earlier investigations of the influence of geomagnetic activity on radio wave absorption were based on storm selection criterion: \Sigma K_P >= 30. This criterion lumped together weak, moderate, and strong storms, and favouring weak and moderate storms made it impossible for the investigations to detect any change in equatorial radio wave absorption following geomagnetic storms. Presently, the effect of geomagnetic storms on equatorial radio wave absorption has been investigated using severe storms (Ap > 54) and HF absorption data obtained at 4.87 MHz at 1000 hours LT at Lagos (3.40°E, 6.55°N). The absorption data were measured using radio waves reflected from the F region, and the transmitter (Radio Cotonou) is located at Cotonou (2.43°E, 6.35°N). The present results obtained using the superposed epoch method show that HF absorption in the equatorial ionosphere increases after severe geomagnetic activity.

Keywords: A3 method; equatorial region; geomagnetic activity; radio wave absorption; superposed epoch analysis

PHASE PARADOX IN THE BÉKÉS BASIN AND A POSSIBILITY FOR ITS RESOLUTION BY 2D/3D MODELLING

Acta Geod. Geoph. Hung., Vol. 36(2), pp. 133-152 (2001)

A Ádám and M Kis

Geodetic and Geophysical Research Institute
of the Hungarian Academy of Sciences
H-9401 Sopron, POB 5, Hungary

[Manuscript received February 8, 2001]

In the area of the typical 3D B‚k‚s basin ("graben") high anisotropy (difference) appears in the extreme values of the magnetotelluric impedance phases in the period interval corresponding to the indication of the conductive asthenosphere. As proved by the forward 2D/3D modelling, this anisotropy can only be explained by a strong 2D effect. This fact may confirm the validity of the results of the 2D inversion of PGT1 magnetotelluric data indicating the upwelling of the asthenosphere below the Békés basin.

Keywords: anisotropy; asthenosphere; impedance phase; magnetotellurics; sedimentary basin

LOCAL GEOID DETERMINATION BASED ON GRAVITY GRADIENTS

Acta Geod. Geoph. Hung., Vol. 36(2), pp. 153-162 (2001)

L Völgyesi

Department of Geodesy and Surveying
Budapest University of Technology and Economy
H--1521 Budapest, Hungary
e-mail: lvolgyesi@epito.bme.hu

[Manuscript received November 14, 2000]

There is a good possibility to interpolate a dense net of deflections of the vertical from W_yy-W_xx and W_xy gravity gradients measured by torsion balance and applying astronomical levelling to compute geoid heights. A new practical computation of astronomical levelling is suggested.

Keywords: astronomical levelling; deflection of the vertical; gravity gradients; local geoid; torsion balance measurements

FULFILMENT OF THE LAW OF LARGE NUMBERS IN CASE OF VARIANCE DETERMINATIONS

Acta Geod. Geoph. Hung., Vol. 36(2), pp. 163-174 (2001)

B Hajagos¹ and F Steiner²

¹Institute of Mathematics, University of Miskolc
H--3515 Miskolc, Egyetemváros, Hungary
²Geophysical Department, University of Miskolc
H--3515 Miskolc, Egyetemváros, Hungary

[Manuscript received November 30, 2000]

As the variance (the square of the minimum L₂-norm, i.e., the square of the scatter) is one of the basic characteristics of the conventional statistics, it is of practical importance to know the errors of its determination for different parent distribution types. This statement is outstandingly valid for the geostatistics because the \gamma(h) variogram (called also as semi-variogram) is defined as the half variance of some quantity-difference (e.g. difference of ore concentrations) in function of the h distance of the measuring points and this \gamma(h)-curve plays a basic role in the classical geostatistics.

If the scatter (\sigma_VAR) is chosen to characterize the determination uncertainties of the variance (denoted the latter by VAR), this can be easily calculate as the quotient A_VAR / n^0.5 (if the number n of the elements in the sample is large enough); for the so-called asymptotic scatter A_VAR is known a simple formula (containing the fourth moment). The present paper shows that the A_VAR has finite value unfortunately only for about a quarter of distribution types occurring in the earth sciences, it must be especially accentuate that A_VAR has infinite value for that distribution type which most frequent occurs in the geostatistics.

It is proven by the present paper that the law of large numbers is always fulfilled (i.e., the error always decreases if n increases) for the error-determinations if the semi-intersextile range is accepted (instead of the scatter); the single (quite natural) condition is the existence of the theoretical variance for the parent distribution.

Keywords: asymptotic scatter; asymptotic semi-intersextile range; higher moments; law of large numbers; scatter; semi-intersextile range; variance

ON THE SPATIO TEMPORAL DISTRIBUTION OF GLOBAL SEISMICITY AND ROTATION OF THE EARTH -- A REVIEW

Acta Geod. Geoph. Hung., Vol. 36(2), pp. 175-187 (2001)

D Shanker¹, Nipun Kapur², V P Singh³

¹Department of Earthquake Engineering
University of Roorkee
Roorkee--247 667, India>
e-mail: dayasfeq@rurkiu.ernet.in
²GE Capital International services
Race Course Road, Bangalore--560 001, India
e-mail: Nipun.Kapur@geind.ge.com
³Department of Geophysics
Banaras Hindu University, Varanasi--221 005, India

[Manuscript received April 11, 2000, revised December 14, 2000]

This article reviews the development of the study of relationship between the earth's rotation and the spatio-temporal distribution of global seismicity by stationary model of seismicity rates and annual seismic energy released. Observed variations of seismic energy release in shallow, intermediate and deep focus earthquakes and their frequency distribution confirms this correlation. The peaks of these parameters are controlled by the earth rotation. There exists a phase relationship among earth's rotation rate minima and maxima with the maxima (peaks) of the above parameters as well as Thrust (T) and the strike slip (S) dominating periods of global seismicity.

In order to compare our results with observations, the space-time dependence of the frequency of earthquakes and annual energy release has been established. The results are in very good agreement with previous studies and further enhance our knowledge for global seismicity distribution.

Keywords: Chandler wobble; dynamic oblateness; quality factor; spatio-temporal; straining

TOMOGRAPHIC IMAGING OF THREE-DIMENSIONAL P-WAVE VELOCITY STRUCTURE BENEATH THE PANNONIAN BASIN

Acta Geod. Geoph. Hung., Vol. 36(2), pp. 189-206 (2001)

Z Bus

Geodetic and Geophysical Research Institute
of the Hungarian Academy of Sciences
Seismological Observatory
H--1112 Budapest, Meredek u. 18
e-mail: bus@seismology.hu

[Manuscript received September 25, 2000]

Tomographic P-wave velocity inversion has been performed for the Pannonian region using first arrival times of local and regional events from the bulletins of the International Seismological Center and the Hungarian Earthquake Bulletins. The input data consist of 4071 arrival times of 570 events. A three-dimensional velocity model has been gained by joint hypocenter-velocity inversion on a coarse and a fine non-uniform cartesian grid of nodes. The initial one-dimensional model was determined by genetic algorithm. A bending ray tracer has been used to calculate the theoretical travel times and ray paths. The reliability of the inverted velocity parameters were checked by the checkerboard method and by the analysis of the model resolution matrix. The results are generally in agreement with the known structural characteristics of the Pannonian Basin. An interesting high-velocity anomaly has been found in the uppermost mantle beneath the southern part of the Great Hungarian Plain.

Keywords: genetic algorithm; high-velocity anomaly; Pannonian Basin; seismic waves; velocity inversion

PRECIPITATION PREDICTION WITH NEURAL NETWORKS

Acta Geod. Geoph. Hung., Vol. 36(2), pp. 207-216 (2001)

L Bodri

Res. Group Geophys. Envir. Phys., Hung. Acad. Sci.
c/o Geophys. Dept., Eötvös Univ.
1083--Budapest, Ludovika t‚r 2, Hungary
e-mail: bodri@gis.elte.hu (bodri@pangea.elte.hu)

[Manuscript received February 2, 2000]

Dramatic floods occurred in Central Europe in recent summers, Hungary having been seriously affected in its eastern part. Predictive approach based on modeling flood recurrence may be helpful in flood management. Summer floods are typically characterized by saturated catchment due to long-lasting heavy precipitation followed by a sudden extreme rainfall. In present work, an artificial neural network (ANN) models were evaluated for precipitation forecasting. A back propagation neural networks were trained with actual annual and monthly precipitation data from east Hungarian meteorological stations for a time period of 38 years. Predicted amounts are next-year-precipitation and summer precipitation in the next year. The ANN models provided a good fit with the actual data, and have shown a high feasibility in prediction of extreme precipitation.

Keywords: flood; neural network; prediction; precipitation

INVESTIGATIONS ON THE PERIODS OF TRANSITION IN THE MESOPAUSE DURING SPRING AND AUTUMN

Acta Geod. Geoph. Hung., Vol. 36(2), pp. 217-224 (2001)

W Schröder

Hechelstrasse 8, D-28777 Bremen Roennebeck, Germany

[Manuscript received June 4, 1999]

Using indirect method (observation of noctilucent clouds from the northern hemisphere) a number of mesospheric processes can be continuously monitored. In this paper, start and end of the seasonal transitions in the regional of the mesopause during the years 1966/1968 have been analysed. It is shown that the mesospheric circulation which begins in spring in lower altitudes of the atmosphere will reach the mesopause later. In autumn, the warming (absence of noctilucent clouds) starts at the 8 km level and reaches lower altitudes of the atmosphere during the winter months. The duration of seasonal transitions in the thermal structure of the mesopause is about 4--5 weeks; the rate of downward drifting is approximately 1 km per month. Some aspects of stratospheric-mesospheric coupling are discussed in the last section of the paper.

Keywords: mesopause; mesospheric temperature; noctilucent clouds; summer circulation; winter circulation

WHY RESEARCH INTO THE HISTORY OF GEOSCIENCES?

Acta Geod. Geoph. Hung., Vol. 36(2), pp. 225-229 (2001)

W Schröder

Hechelstrasse 8, D-28777 Bremen Roennebeck, Germany

[Manuscript received August 30, 1999]

Keywords: history and philosophy of sciences; history of geophysics; IUGG

FUNDAMENTAL LEVELLING NETWORKS AND HEIGHT DATUMS AT THE TERRITORY OF THE REPUBLIC OF CROATIA

Acta Geod. Geoph. Hung., Vol. 36(2), pp. 231-243 (2001)

N Rozic

Faculty of Geodesy, University of Zagreb
10000 Zagreb, Kacicéva 26, Croatia

e-mail: nevio.rozic@zg.tel.hr

[Manuscript received July 10, 2000]

In the Republic of Croatia there is a long tradition going on in carrying out systematic levelling works. These works have resulted, in the period of about 120 years, with the establishment of three fundamental levelling networks of geometric levelling. These are precise levelling network of the Austro-Hungarian Monarchy, I. levelling network of high accuracy and II. levelling network of high accuracy of former Yugoslavia. These networks are the basis of height system of the Republic of Croatia, and accompanied by adequate definitions of height datums they are used even today for solving fundamental and applied geodetic tasks and scientific researches.

Keywords: geometric levelling; height datum, height system; levelling network

OVERVIEW OF SCIENTIFIC ACTIVITIES IN GEOMAGNETISM AND AERONOMY IN CROATIA

Acta Geod. Geoph. Hung., Vol. 36(2), pp. 245-255 (2001)

I Lisac

Andrija Mohorovicic Geophysical Institute
Faculty of Science, University of Zagreb
Horvatovac bb, 10 000 Zagreb, Croatia

e-mail: lisac@rudjer.irb.hr

[Manuscript received December 5, 2000]

Comments to papers on historical data and studies related to activity in geomagnetism and aeronomy, collected over Croatian territory are presented. This way a general overview of historical development of these scientific branches in Croatia is obtained.

Keywords: aeronomy in Croatia; atmospheric electricity; atmospheric tides; aurora; geomagnetism in Croatia; ozone

Number 3

NOTE ON THE ESTIMATING THE SUN'S RADIATION OUTPUT DURING THE MAUNDER MINIMUM AND THE PROBLEM OF SOLAR VARIABILITY

W Schröder¹ and H-J Treder²

¹Hechelstrasse 8, D-28777 Bremen Roennebeck, Germany
²Rosa-Luxemburg-Strasse 17a, D-14282 Potsdam, Germany

[Manuscript received August 30, 1999]

The general problem of solar variability (including the solar constant and various minima) is discussed in detail. We have no theoretical arguments about the amplitudes of the solar cycle, today. A new point is the statement of White et al. (1992) on the temperature of solar-type non-cycling stars. The theorems of the creation and annihilation of vorticity and magnetical fields prove that these processes essentially have a thermodynamical component.

Keywords: Maunder minimum; solar constant

ON LATITUDE DEPENDENCE OF GEOMAGNETIC STORM AFTER-EFFECTS IN IONOSPHERIC ABSORPTION

V U Chukwuma

Department of Physics
Ogun State University
Ago-Iwoye, Nigeria
e-mail: victorchukwuma@yahoo.com

[Manuscript received March 7, 2001]

HF absorption enhancements following major geomagnetic storms are analysed, using the superposed epoch method, to examine the geomagnetic latitude limit of the after-effect phenomenon. The absorption data was obtained from one double hop and two single hop A3 transmission paths with ionospheric points at F _geomag = 3.54 ^oN and ~ 6.40 ^oN(15.40 MHz), F _geomag ~ 9 ^oN(4.87 MHz), and F _geomag ~ 11 ^oN(6.09 MHz) respectively. Presently, the results have shown that enhancement in absorption following major storms could be traced to the low latitude of 3.54 ^oN.

Keywords: A3 method; geomagnetic activity; geomagnetic latitude; HF absorption; solar wind

SIMULTANEOUS MEASUREMENTS OF THE ATMOSPHERIC ELECTRIC POTENTIAL GRADIENT AT NAGYCENK OBSERVATORY BY MEANS OF TWO INDIVIDUAL EQUIPMENTS

F Märcz, J Horváth, P Bencze, G Sátori, J Bór

Geodetic and Geophysical Research Institute
of the Hungarian Academy of Sciences
H--9401 Sopron, POB 5, Hungary

e-mail: marcz@ggki.hu

[Manuscript received April 25, 2001]

In addition to the original equipment, a new measuring set has been constructed for observing the atmospheric electric potential gradient (PG) at Nagycenk station. The study describes this new set and reports on PG variations derived from data obtained by the two simultaneous measurements. Both runs of the mean diurnal variations determined on the basis of the two data sets are quite similar, as well as they resemble the appropriate diurnal variation derived from earlier Nagycenk data, or fairly the 'Carnegie Curve'. Nevertheless, the measured PG level is somewhat higher in the case of the new equipment (PG 2) than that measured with the original set (PG 1). This is also true in the case of single day’s diurnal variations, however, the daily runs derived from the individual measurements are hardly different. Whichever of the two data sets is applied, the PG's seasonal (annual) variation shows a distinct maximum in winter, even if this maximum is again higher for PG 2 than that for PG 1. Certain ideas on this behaviour are also suggested by the study.

Keywords: atmospheric electric potential gradient; diurnal variation; measuring equipment; seasonal variation

A COMPACT DERIVATION OF BASIC RELATIONSHIPS TO DETERMINE SUBSURFACE RESISTIVITY FUNCTIONS

L Szarka

Geodetic and Geophysical Research Institute of the Hungarian Academy of Sciences, H-9401 Sopron, POB 5, Hungary

e-mail: szarka@ggki.hu

[Manuscript received July 12, 2001]

Starting from the magnetic vector potential and the electric scalar potential a compact derivation is given to determine the one-dimensional subsurface resistivity function in different ways, leading to the basic relationships of the classical magnetotelluric and the magnetovariational methods. With measurements on the horizontal ground surface Schmucker's C-response and the surface impedance can be determined by using two different combinations of the electromagnetic field components. With measurements at more than one height (depth) levels (assuming the knowledge of horizontal and/or vertical gradients) some further theoretical possibilities emerge.

The novelty of the paper lies first of all in the very compact presentation of the one-dimensional case, introducing a local distortion due to a small-size inhomogeneity.

Keywords: magnetotellurics; magnetovariation; subsurface resistivity

LOCALISATION AND DIRECTION DETERMINATION OF FISSURES WITH GEOELECTRIC METHODS IN NARROW, ELONGATED MEASURING AREAS

S Szalai¹, M Abd Alla², S Ahmed², L Szarka¹

¹Geodetic and Geophysical Research Institute
of the Hungarian Academy of Sciences
H-9401 Sopron, POB 5, Hungary
e-mail: szalai@ggki.hu
²National Research Institute of Astronomy and Geophysics
Helwan-Cairo, Egypt
e-mail: argharreb@frcu.eun.eg

[Manuscript received July 23, 2001]

In this paper we provide a field example for the determination of the location and direction of fissures in narrow, elongated measuring areas. The test measurements were carried out on the Mokattam plateau at Cairo (Egypt). Direction, length of the layout and the profile length all were very limited, since the measurements had to be carried out within a narrow (2--10 m wide) stripe, between a built-in area and a cleft rim. Interpretation of field measurements was supported by (1) analogue model experiments, and (2) parameter sensitivity maps. As it was found from laboratory experiments, fissures are indicated by potential-difference maximums along profiles measured by using three-electrode array (if the reference point is between the potential electrodes). The mean distance between two neighbouring maximums throughout the whole profile was found to be about 3--4 m, corresponding to the distance between the most visible fissures on the cleft wall. The Schlumberger null-array has been found to be an appropriate tool in determination of the direction of fissures. Its resolution is higher than that of the classical Schlumberger array. Its only disadvantage is that on the azimutal diagram it gives two times more minimum pairs than the number of fissures. Among such constrained circumstances the best method to get useful information about location and direction of fissures in the subsurface limestone is to use jointly corresponding traditional and null-arrays. While the location is given best by traditional three-electrode array measurement, the direction of the fissures is given from the joint interpretation of the Schlumberger null-array and the traditional Schlumberger array. In this way it is to separate several fissure directions.

Keywords: analogue modelling; fissure direction; geoelectrical null-arrays; parameter-sensitivity map

REFRACTION IN LEVELING AND A METHOD FOR ITS DETERMINATION --- THEORETICAL BASIS

O A Mozzhukhin

Nizhny Novgorod State University of Architecture and Building
603155 Nizhny Novgorod
Trudovaya 25--22, Russia

[Manuscript received August 21, 2000]

The curvature of the trajectories of propagation of optical rays in the atmosphere (refraction) is one of the basic effects which causes systematic errors in the height determination by leveling and moreover which is very difficult to take into account. In spite of quite intensive investigations during many years, it remained a problem that could not obtain practical solution. Using the methodological principles of the theory of similarity and modeling, the author succeeded in obtaining a basically new solution of the task. This solution enabled the development of a technological method to determine refraction in high precision and trigonometric leveling. The application of the method needs negligible surplus measurements.

Keywords: leveling; refraction; optical ray

LOCAL SEASONAL GRAVITY CHANGES IN THE LOWER RHINE EMBAYMENT, GERMANY

Ch J Keysers¹, H-J Kümpel², J Campbell¹

¹Geodetic Institute
University of Bonn
Nussallee 17, 53115 Bonn, Germany
e-mail: mail@ckeysers.de
²Geological Institute
University of Bonn
Nussallee 8, 53115 Bonn, Germany

[Manuscript received November 30, 2000]

Repeated high resolution gravity measurements with LaCoste and Romberg gravity meters have been carried out for nearly two years in the Lower Rhine Embayment, Germany. In the long run, the observations aim at detecting long term gravity changes that are associated with surface subsidence due to groundwater withdrawal in a nearby browncoal mining area. Concurrently, short term gravity variations on local scales are also investigated to find out their influence on long term gravity observations. For that reason, two local networks with extensions of a few kilometers each have been set up, one of them across an active fault where presently large height changes are occurring (up to 2.2 cm/a ), the other one in a stable intra-block site showing no changes of height. The gravity data, so far, do not reveal any significant long term changes. However, seasonal variations of up to 500 nms^-2 are observed between stations on both sides of a steeply dipping tectonic fault. This is where significant height changes due to ground water withdrawal occur, while gravity differences between stations on the same side of that fault as well as the observations in the other network remain constant throughout the observation period. The physical reason for the gravity variations is not yet clear. We assume, that different types of vegetation and soil cause seasonal changes in soil moisture, and thus in subsurface density. This study emphasizes that stations for repeated high precision gravity observations (aiming e.g. to detect seismogenic precursory anomalies) may be largely influenced by local, effects of presumably hydrological origin and that networks even on the 100 m scale can considerably suffer from systematic distortions.

Keywords: gravimetry; gravity variations; hydrological influence; subsidence

PRACTICAL --- BUT MYSTERIOUS --- BEHAVIOUR OF THE MOST FREQUENT VALUES

F Steiner F¹ and B Hajagos²

¹Geophysical Department
University of Miskolc
H--3515 Miskolc, Egyetemváros, Hungary
²Institute of Mathematics
University of Miskolc
H--3515 Miskolc, Egyetemváros, Hungary

[Manuscript received June 25, 2001]

The paper proves the practically advantageous fact that for the determination errors of the most frequent value calculations the simple asymptotic rule is valid for the whole sample-size domain \infty > n >= 4.

Keywords: arithmetic mean; asymptotic rule; dihesion; Monte-Carlo-calculation; most frequent value; sample median; semi-intersextile range

RELATIVE ORIENTATION OF IMAGES TAKEN BY NON-METRIC CAMERAS USING 2D PROJECTIVE TRANSFORMATIONS AND ROBUST ESTIMATION

L Battha

Geodetic and Geophysical Research Institute
of the Hungarian Academy of Sciences
H-9401 Sopron, POB 5, Hungary
e-mail: battha@ggki.hu

[Manuscript received March 28, 2001]

The paper deals with the robust estimation of relative orientation parameters without making use of interior orientations. 2D projective transformations are used to produce rectified stereo-pair images.

Keywords: Cauchy-function; epipolar rays; gradient method; image-plain; robust estimation

FILTERING OF EARTH'S POLAR MOTION USING TRIGONOMETRIC INTERPOLATION

J Závoti

Geodetic and Geophysical Research Institute
of the Hungarian Academy of Sciences
H-9401 Sopron, POB 5, Hungary
e-mail: zavoti@ggki.hu

[Manuscript received August 9, 2001]

The annual wandering of Earth's pole takes place in an area about 200 m². Within this area, the amplitudes of the displacements due to Earth tide and global meteorological processes do not exceed a few decimetres. Obviously, very precise measuring technique is necessary for the examination of the above phenomena. Nowadays, these are primarily the devices and the methods of cosmic geodesy. From them, on the basis of Ádám (1990) the VLBI (Very Long Baseline Interferometry), and the SLR (Satellite Laser Ranging) are able to show the variations of the pole with periods between one day and one year. The GPS (Global Positioning System) and the developed processing system of VLBI are suitable for the examination of processes within a day.

Keywords: filtering; Fourier transform; polar motion; timeseries analysis; trigonometric interpolation

SEISMICITY AND RECENT CRUSTAL MOVEMENT STUDIES IN AND AROUND THE GREATER CAIRO REGION, EGYPT

Abd El-Monem Sayed Mohamed

National Research Institute of Astronomy and Geophysics
Helwan, Cairo, Egypt

[Manuscript received August 22, 2000]

On 12th October 1992 Egypt was hit by one of the largest earthquakes with magnitude of m_B = 5.9. This earthquake occurred at the Dahshour region 35 km south-west of the center of Cairo (the Capital). Widespread damage occurred in the cities Cairo and El-Faiyum and in many villages in the epicentral area. Different geophysical and geodetic investigations were performed in and around the greater Cairo region. This paper focuses on the results obtained by the analysis of GPS measurements and earthquake data. The main aim of these studies are mapping of the tectonic elements presented within the region under investigation, to understand the geodynamics of the region and to have a better understanding about the cause of the earthquake occurrence and its origin. Also we try to find the possible association between crustal deformation and earthquake activity in and around the greater Cairo region.

Keywords: crustal movement; Egypt; geodetic network; seismicity

COMMENTS TO THE PAPER I LISAC, ``OVERVIEW OF SCIENTIFIC ACTIVITIES IN GEOMAGNETISM AND AERONOMY IN CROATIA''

W Schröder

Geophysical Commission
Hechelstrasse 8, D-28777 Bremen-Roennebeck, Germany

[Manuscript received August 31, 2001]

The auroral data from Croatia are of great interest as examples from middle latitude stations. The descriptions given by Lisac are not new; in general the development of auroras is well described from many observations in middle latitudes, e.g. from Germany (Schröder 1964). The auroral phenomenon of November 11, 1991 is also well-documented from other European parts. It is of more interest to have details on the earliest observations from Croatia after the so-called Maunder-Minimum (1645--1715). The indicated years in Lisac's report are connected with times of solar maxima (1738.7 and 1750.3). Many auroras have been reported in the years 1737 and 1750 by European observers. During or near the solar minima (1734.0 and 1745.0) auroras were seldom observed in Central Europe, and consequently very seldom in the latitudes of Croatia and other places. It is known that after 1710 the interest in auroras increased in Europe. A key event was the great aurora of March 17, 1716 (see Schröder 2001). Following this event a general discussion started on the physical nature of these phenomena, and C Wolff (see Schröder 2001) and others pointed out their natural origin. Since this time auroras have been mostly well-documented from middle latitudes and interpreted as atmospheric phenomena.

GEORG VON NEUMAYER (1826--1909) AND INTERNATIONAL GEOPHYSICS --- A CASE STUDY WITH SPECIAL REMARKS ON GEOMAGNETIC RESEARCH

W Schröder¹ and K-H Wiederkehr²

¹Geophysical Commission
Hechelstrasse 8, D-28777 Bremen-Roennebeck, Germany
²Birkenau 24
D-22084 Hamburg, Germany

[Manuscript received September 3, 1999]

Neumayer was a prominent figure in the development of geophysics in the 19th century as he organised a network of international co-operation in this new field of science. The authors analyse in this paper his contributions to terrestrial magnetism. Neumayer was in this field a research worker and thinker, too, as well as a stimulating co-ordinator. He published in 1892 an excellent Atlas of Geomagnetism as part of Berghaus' Physikalischer Atlas.

Keywords: geomagnetic charts; International Polar Year; Neumayer G; Schmidt A; ship compass

Book reviews

B Hofmann-Wellenhof, H Lichtenegger, J Collins: GPS Theory and Practice
Fifth, revised edition. Springer, Wien--NewYork, 2001, 382 pp, 45 figs

L Bányai

W Schröder ed.: Historical Case Studies in Physics and Geophysics -- Case Studies.
Beiträge zur Geschichte der Geophysik and Kosmischen Physik, Vol. 2, No. 1 and Newsletter No. 43 IAGA-IDCH, Bremen, 2001, 204 pp

J Verõ

Number 4

OBSERVATIONS AND RESULTS OF GPR MODELLING OF SINKHOLES IN UPPER SILESIA (POLAND)

J Zietek¹, J Karczewski¹, S Tomecka-Suchon¹, J Carcione², G Padoan², C Denis^3*

¹University of Mining and Metallurgy (AGH)
Institute of Geophysics
30 Al. Mickiewicza, PL 30-059 Kraków, Poland
²Osservatorio Geofisico Sperimentale
POB 2011 - Opicina, I-34016 Trieste, Italy
³Institut d'Astrophysique et de Géophysique
Université de Liège, 5 Avenue de Cointe
B--4000 Liège, Belgium
e-mail: denis@astro.ulg.ac.be
^*corresponding author

[Manuscript received July 30, 2001]

Using a RAMAC-GPR with a 200 MHz antenna, we obtained radargrams in an old coal-mining district of Upper Silesia (Poland), where exploitation holes represent a danger of collapse for existing structures. Despite some drawbacks, GPR methods seem to be the best technique for mapping and monitoring these holes, which may reach the surface after some time. In the first part of this paper, we show actual field measurements for a typical case, and in the second part we present preliminary theoretical investigations. We construct 2D synthetic radargrams based on the information we obtained from available geological data and the interpretation of the real radargrams. Thus, we formulate suggestions on how to optimize the methodology of locating sinkholes by the GPR technique, and give some clues concerning the theoretical interpretation of GPR data in this particular case.

Keywords: applied geophysics; coal mining, Upper Silesia; field measurements; ground-penetrating radar, GPR; sinkholes; theoretical modelling

INVESTIGATION OF GROUND AND OBJECT MOTIONS AT THE TV TOWER IN SOPRON, HUNGARY

G Mentes¹ and M Fabian²

¹ Geodetic and Geophysical Research Institute
of the Hungarian Academy of Sciences
H--9400 Sopron, Csatkai E. u. 6-8., Hungary
e-mail: mentes@ggki.hu
²Collaborative Research Center (SFB 350)
Section of Applied Geophysics, Geological Institute
University of Bonn
Nussallee 8, D--53115 Bonn, Germany

[Manuscript received June 5, 2001]

The investigation of the coupling between building and ground motions is of great importance because the results contribute to the planning of stable, motion-proof constructions and to forecast of damages. For monitoring ground and building motions the TV tower in Sopron, Hungary was chosen. Two borehole tiltmeters, Applied Geomechanics Inc., model 722A were used for continuous and short-term high frequency tilt measurements. One of the instruments was installed on the concrete basement of the TV tower and the other in a borehole drilled at a distance of about 90 m beside the tower. This paper presents continuous data series of a length of more than one year, high frequency tilt measurements with sampling rates of up to 10 Hz and discusses the first experiences of the observations.

Keywords: borehole tiltmeter; broad band deformation measurements; ground and building movements

RELIABILITY OF THE ESTIMATIONS OF THE CORRELATION COEFFICIENT

F Steiner¹ and B Hajagos²

¹Geophysical Department, University of Miskolc
H--3515 Miskolc, Egyetemváros, Hungary
²Institute of Mathematics, University of Miskolc
H--3515 Miskolc, Egyetemváros, Hungary

[Manuscript received September 7, 2001]

On the basis upon n corresponding value-pairs (x_i, y_i), i=1, ..., n, the closeness of correspondence between the random variables x and h is customarily characterized by the classical correlation coefficient r (see Eq. 2 in the present paper), equally in the geosciences and in the everyday life. It is shown in the present paper the lack of the robustness of Eq. (2) (r has even no meaning for circa 40 % of the types occurring in the geosciences), and the lack of the resistance (one single outlying value-pair can distort the r-value in an incredible degree).

The modern correlation coefficient r_rob (see Eq. 9 in this paper) is completely resistant against outliers, and in the same time also robust: Eq. (9) is applicable even if x and h are of Cauchy type, very far lying from the Gaussian distribution and even from the most frequently occurring so-called statistical distribution (see Eq. 6). For the Cauchy distribution neither the scatter (variance) nor the expected value exist therefore for this distribution-type even the classical theoretical value (see Eq. 3) does not exist: the calculation of r according to Eq. (2) gives in this case an "estimation" of a not existing quantity.

In the paper are presented the results of a time consuming series of Monte Carlo calculations made equally for the statistical and Gaussian distributions and for n = 10, 30 and 100; the errors characterized by the semi-interquartile and semi-intersextile ranges of the modern r_rob (Eq. 9) were calculated and tabulated for r_t = 0, 0.1, 0.2, ... 0.7 and 0.8. An approximate method is also given (see the simple Eqs. 16 and 17) to determine that value of n which assures a prescribed accuracy of the modern r_rob.

Keywords: correlation coefficient; Monte Carlo method; resistance; robustness

RESEARCH FOR SEISMOGENIC ZONES IN THE PANNONIAN BASIN --- A DETERMINISTIC SEISMIC HAZARD ESTIMATION FOR BUDAPEST

Gy Szeidovitz¹, Z Bus¹, K Gribovszki²

¹Geodetic and Geophysical Research
Institute of the Hungarian Academy of Sicences
H--1112 Budapest, Meredek u. 18, Hungary
e-mail: szeido@seismology.hu
² Geodetic and Geophysical Research Institute
of the Hungarian Academy of Sciences
H--9400 Sopron, Csatkai E. u. 6-8., Hungary

[Manuscript received March 5, 2001]

In this paper, a theory describing the possible origin of shallow depth earthquakes occurring within the sedimentary depressions of the Pannonian Basin is presented. In addition, the seismicity of Budapest is re-evaluated by synthetic seismogram based deterministic seismic hazard estimation.

Keywords: depression basin; earthquakes; faults; seismic hazard

DISCRIMINATION OF QUARRY-BLASTS FROM EARTHQUAKES USING SPECTRAL ANALYSIS AND CODA WAVES IN HUNGARY

M Kiszely

¹Geodetic and Geophysical Research
Institute of the Hungarian Academy of Sicences
H--1112 Budapest, Meredek u. 18, Hungary
e-mail: kiszely@seismology.hu

[Manuscript received March 21, 2001]

In the seismological research it is very important to use a correct earthquake catalogue that provides a strong basis for indicating seismic sources and for developing seismotectonic models. Homogeneity is expected from the catalogue and desirable to indicate data that are derived from explosions. The spectral analysis provides means to discriminate explosions from earthquakes. The quarry-blasts have simpler spectra than earthquakes. We estimate coda attenuation Q_c for quarry-blasts that occurred in Vértes mountains. It has been found that the coda decay rate Q_c is significantly lower for quarry-blasts than for earthquakes. At 6 Hz and 10 Hz there are great differences between explosions and earthquakes.

Keywords: coda waves; quarry-blast; spectral analysis

THE APPLICABILITY OF THE HORIZONTAL TO VERTICAL SPECTRAL RATIO IN SITE EFFECT EVALUATION

E Bánné Gyõri

MTA-ELTE Geophysics and Environmental Physics Research Group
Eötvös Loránd University, Department of Geophysics
H--1083 Budapest, Pázmány P. sétány 1/C, Hungary
e-mail: gyori@pangea.hu

[Manuscript received October 8, 2001]

It is well known that surface geology may significantly affect strong ground motion and hence it should be incorporated into seismic hazard estimation at a specific site. Numerical and empirical methods are used to determine the site effect. On areas with moderate seismicity the empirical methods are based on microtremor measurements. Solely the single station methods, for example the H/V spectral ratio technique, could be used in the absence of a nearby reference station situated on rock site. The one year long noise measurements of 8 stations belonging to the Hungarian Microseismic Monitoring Network have made it possible the testing of this method. The stations are situated in the middle part of Hungary. All seismometers are triaxial LE-3D high sensitivity 1 Hz geophones. Three stations are situated on hard rocks while five ones on loose site above a deep sedimentary basin with more than 1000m thick sediments. The large amount of noise data have made it possible to examine the stability of the method. The examinations have shown that the computed spectral ratio curves are very stable in time. While all stations on rock sites show nearly flat H/V spectral ratio, all stations on soft sites show a peak at very low, 0.1--0.2Hz frequencies. Analytical computations have been carried out to verify this low frequency behaviour and have shown that these peaks are due to the fundamental frequency of the overall sediment thickness. H/V ratios have also been calculated from seismograms of weak local earthquakes, so they could be compared with ratios obtained from noise measurements.

Keywords: empirical methods; horizontal to vertical spectral ratios; microtremors; seismic hazard; site effect

EULER, THE THEORY OF GRAVITATION AND SOME GEOPHYSICAL ASPECTS

W Schröder¹ and H-J Treder²

¹Hechelstrasse 8, D-28777 Bremen Roennebeck, Germany
²Rosa-Luxemburg-Strasse 17a, D-14282 Potsdam, Germany

[Manuscript received October 15, 1999, revised January 24, 2000]

Euler's results concerning the theory of gravitation are discussed in this paper in order to give an insight into the scientific problems of Euler's age and his relation to Newton's work. Geophysical aspects are emphasized in his work.

Keywords: Euler; Newton; theory of gravitation

THE GENERAL RELATIVISTIC AND COVARIANT FORM OF THE I. HELMHOLTZ VORTICITY THEOREM AND GEOPHYSICAL APPLICATION

W Schröder¹ and H-J Treder²

¹Hechelstrasse 8, D-28777 Bremen Roennebeck, Germany
²Rosa-Luxemburg-Strasse 17a, D-14282 Potsdam, Germany

[Manuscript received November 8, 1999, revised February 25, 2000]

The general relativistic and covariant differential form of Helmholtz's first vorticity theorem is presented. We prove in relation with it an invariant kinematic identity which is the generalisation of the Helmholtz theorem for general continua.

Keywords: geophysical hydrodynamics; Helmholtz vorticity theorem; invariant kinematic identity

Curriculum vitae --- József Somogyi

J Závoti

Constructed by Judit.Szendroi@ggki.hu

Updated: October 30, 2001