The paper analyzes homogeneous data of vapour pressure and relative humidity recorded at the Zagreb-Grič observatory between 1944 and 1978.
The mean annual course of vapour pressure resembles that of air temperature. Relative humidity in the mean annual course decreases from January to April, increases from April to June, slightly decreases from June to July, and then increases until December; the major minimum in April is due to sudden heating of air, and the major maximum in December is due to the prevalence nightly air cooling. Singularities of vapour pressure (August 13-16) and of relative humidity (January 21-27, May 4-9, June 8-15, December 21-27) have also been determined.
The mean diurnal course of vapour pressure has its major minimum early in the morning, and its maximum is in the afternoon; from June until October unpronounced secondary afternoon minimum appears. Relative humidity mean diurnal course has its maximum about sunrise, and its minimum is in the afternoon.
In the 1944 – 1978 period, vapour pressure does not show a pronounced trend, while relative humidity tends to increase in August and September.
Numerous atmospheric processes are reflected in the vapour pressure data and the relative humidity data recorded on Grič. The processes are air advection, daily heating and nightly cooling of air, evapotranspiration, condensation, sublimation, vapour diffusion, vertical air mixing, subsidence, cyclonal activity (precipitation, increased cloudiness), European monsoon, foehn influence of the Dinaric mountains and the Alps, and, finally, the urban influence. A combination of these processes often increases or decreases the vapour pressure or relative humidity. The influence of these processes is generally not constant throughout the year.
are the surface airflow characteristics in
paper deals with ground values of incoming Solar
energy in the 41° – 47°N zone and in the 0 – 3000 metre altitude
range, on the assumption of Rayleigh atmosphere model. The analysis is based on
daily global radiation. A comparison with measured data shows that daily
radiation for Rayleigh atmosphere model as a rule exceed that of real daily
radiation near the ground, especially at little altitudes. The radiation for a Rayleigh
model can be exceeded only rarely, in the case of relatively clear and dry air
and strong reflection on suitable situated clouds or on fresh snow. Rayleigh atmosphere
4. Allegretti, I., D. Skoko and M. Živčić (1984): Earthquake hypocentre determination by analytical presentation of the Wadati’s graphical method (four seismological stations). Geofizika, 1, 169-191. (in Croatian)
In the series of papers about the shallow and deep earthquakes Japanese seismologist K. Wadati presented a graphical
method for the earthquake hypocentre determination. Due to its simplicity, it soon became well known as one of
the best methods for locating near earthquakes. In the first part of
this paper (Paragraphs 1., 2., 3.) all the details of
Wadati’s graphical method are presented. In Paragraph
4. original Wadati’s procedure is
presented in the analytical form. The solution of the
equations (Eqs. 1.-4) of the seismic waves
propagation is sought in the fixed rectangular coordinates. After the necessary
transformations the equations (15) are obtained. This equation is linear in
four unknowns: xo, yo,
and c2. To solve the system it is
necessary to form the equations for four seismological stations. The system
(16) combined with the equation (17) completely defines the position of the
hypocentre and the value of the constant c.
In Appendix A a method of coordinate transformations is presented according to
C. F. Richter (1958). It is somewhat simplified due to the linearity of
coefficients AC and B in the latitudes of
To complete the analysis of the data of an earthquakes, in Paragraph 5. the graphical and the analytical method of the hypocentral time determination are presented. The graphical method is presented by the well known Wadati’s diagram (Wadati, 1933) (Fig. 8 as example) while the analytical method consists in the straight line fitting to the observational data by the least squares method (Eq. 25., 28., -30.).
The describe method for the hypocentre determination cannot be applied when all four seismological stations lie on the straight line. This restriction is discussed in Appendix C where it is shown that in the case of linearity between the station coordinates the corresponding determination (3.C) is vanishing.
In Paragraph 6. an example is presented. The hypocentre of the earthquake of 05. 02. 1969. at 04h 25m GMT is determined applying both graphical (Fig. 3.) and the analytical procedure. Some difficulties that may arise in the graphical procedure are also discussed, in particular the case when the ration mik (Eq. (5)) approaches unity.
It is shown that the analytical method supersedes the graphical one in the precision of the results obtained, convenience of the procedure and the speed of its application, especially when an electronic computer is available.
The original Wadati’s graphical method for the earthquake hypocentre location is already presented in analytical form (Allegretti et al. 1984). However, the described method was restricted to the use of the data of four seismological stations. In this paper the equations (Eq. 1.) of seismic wave propagation are solved for the hypocentre coordinates x, y, z and the constant c = Vp Vs/(Vp-Vs) by the use of the least squares method. Providing that approximate values of x, y, z and c are known (usually it is sufficient to approximate the starting epicentre coordinates x’, y’, with the coordinates of the station with the minimal ts-tp time) the least squares method is applied to the error equations (Eqs. 4.). Due to the high rate of convergence it is sufficient to perform only a few iterations. This enables the use of the greater number of seismological stations and, as a consequence, the greater precision of the results. The error estimation is also possible giving the quantitative measure of the precision of the results obtained. It is also, shown, that Wadati’s method could be extended to include the seismic station height differences. This may be applied in the rock bursts investigations too.
In this paper we considered the influences of the changes of the crust and upper mantle earth model parameters on the Rayleigh waves group velocity dispersion. Final result of such analysis is necessary as the first step in the inversion of dissipation data for the earth interior.
The partial derivatives of the group velocity with respect to the shear wave velocity b density r and the layer thickness d were calculated for the continental earth model PEM of Dziewonski et al. (1975), (Table 1). We have modified the model by adding a thin sedimentary layer on top of it. The Thompson-Haskel matrix method (see Appendix) was used for the calculation of theoretical phase velocity dispersion curves with and without taking earth sphericity into account (Fig. 1). Partial derivatives were calculated by the finite difference method (equations (1), (2)). Figures 2, 3 and 4 represent the partial derivatives curves with respect to b, r and d, respectively. The numbers on the curves denote the layers in which the parameter in question was changed.
The conclusions of the analysis are the following:
(i) Shear wave velocity shows the greatest influence upon the group velocity of Rayleigh waves. The influence of the layer thickness is more expressed, the thinner the layer is.
(ii) Partial derivatives with respect to b have peaks for periods that correspond to wave lengths of 3.45-3.80h (h being the depth to the middle of the layer) except for the fourth layer where the wave length equals 3.15h.
(iii) Changing the layer thickness results mainly in shifting the group velocity curves toward smaller or greater periods without changing the value of the neighbouring extreme.
The macroseismic intensity – distance relation (Eq. 6) is defined through four parameters: coefficient p, epicentral intensity Io, focal depth h and absorption coefficient. All the known methods for parameter estimation were based on “a priori” knowledge of the epicentral intensity and/or used a graphical procedure. Also, the epicentral intensity was taken as discrete variable and the value to the coefficient p was assigned in advance. By considering the epicentral intensity as a continuous variable that can achieve any value greater or equal to the maximum observed intensity, it was possible in this paper to apply the least squares method for parameters determination. The only assumption is that the starting values of the parameters, that are to be determined, are roughly known. The procedure consists in calculating the corrections to the starting values of parameters until the best fit, in the sense of Eq. (17), is obtained. In this way the focal depth determination does not depend on the assumptions contained in the assignment of the epicentral intensity, and the imprecision of the graphical method is avoided. The method could be applied for the determination of any combination of the parameters of Eq. (6), providing that the number of observed isoseismal radii is not less than the number of the parameters to be estimated. In the cases where the number of observed isoseismal radii exceeds the number of the parameters to be estimated, the error estimation is also possible, giving the quantitative measure of the precision of the results obtained. Due to the flexibility of the method and its applicability to the electronic computer the parameter estimation is much faster and more precise than before.
of L. Geiger for earthquake hypocentre location, based on the knowledge of
seismic wave arrival times, is well discussed in seismological literature and
widely used. In this paper a simple extension of the method is suggested. It is
shown that the error equations could be formed from the arrival time differences
of the earthquake phases. In that way it has become possible to include, in the
determination of the hypocentre, the data from the stations with poor timing
system, as well as data from the strong motion records which usually operate
without the absolute time system. Also, due to the lack of accurate timing, it
was often impossible to locate instrumentally earthquakes from the beginning of
this century. The presented method is very convenient for relocation of those