Magnitude spectra are determined for three major earthquakes of the year 1985: the Xianjiang earthquake of 23 August, and the Mexico earthquake of 19 September with its largest aftershock of 21 September. Broad-band recordings obtained at the Central Seismological Observatory of the Federal Republic of Germany (GRF) are used for the analysis. Pass-band seismograms are obtained by way of filtering the broad-band seismogram. The magnitude spectrum of an earthquake is determined from the velocity amplitude for each Fourier component. The magnitude spectrum represents the velocity amplitude density spectrum at the earthquake source scaled in magnitude units. A comparison of the magnitude spectra shows significant differences between the focal parameters of the earthquakes, even if their conventional magnitudes (m b , M s ) are similar.
modelling of observed seismograms using complete synthetic signals obtained
with the normal mode summation (Panza, 1985) is
presented. Both low and high frequency modelling are discussed with several
The Greek seismicity file developed by Makropoulos and Burton (1981) for earthquakes up to 1978 and extended up to 1983 (Makropoulos et al., 1986), is examined in terms of magnitude frequency using Gumbel’s third type asymptotic distribution of extreme values. The forecasting parameters are obtained by subdividing Greek seismicity in a cellular manner. Combination of the Gumbel III earthquake occurrence statistics for each cell with acceleration attenuation law leads to perceptibility curves which give the probability of perceiving specific acceleration levels from each earthquake magnitude up to local upper bound magnitude w. These curves show a peak probability which occurs at similar magnitudes defined as the “most perceptible” earthquake. The range of these “most perceptible” earthquake magnitudes is for an Ms of about 5.3 to 7.2.
results are presented as contouring maps for two average depths of 10 km and 20
km respectively. The features of the contoured perceptibility maps are
compatible with existing hazard maps of
of different categories of local geological conditions to the observed macroseismic intensities in
Attenuation laws are derived using both earthquakes and they are compared to determine the attenuation factors appropriate for different rock types. They are also tested for different azimuths from the macroseismic epicentre in order to assess the influence of the radiation pattern of the earthquake in relation to the degree of attenuation in a specific direction. The comparison of the detailed intensity results with strong motion data from the same area and in different geological formations, indicates that there is some relation between them.
The territory of Slovenia is subdivided into five seismogenetic regions according to their geological, tectonical, and geophysical properties. The seismicity of these regions is determined on the basis of more than 3000 earthquakes contained in the catalogue for Slovenia . Seismically most active part is concentrated in central, south-eastern and south-western Slovenia (zones B 2 , B 3 , and A 2 ).
Temporal energy release, strain release and indexes of seismic activity have been determined for all characteristic regions. Introducing parameter it is shown that a temporal dependence of the activity exists, and further, that and increase of the activity in south-eastern and south-western Slovenia is accompanied by a decrease of activity in its central part, and vice versa.
Variations of b -value in the relation have been determined for the three characteristic regions A 2 , B 2 , and B 3 . They have been correlated with times of occurrence of strong earthquakes. It is shown that most events occurred in time intervals when the b -value was 0.9 or less, or when the trend of the b -value was negative.
Analysis of microseismic and macroseismic data of some earthquakes in our country and comparison with the tectonic characteristics of region points to the conclusion that the fault in the earthquake focus could not always be presented by motion on one plain only.
From those empirical data we also learn the kind of motion in the focus that affects the character of the seismic ground oscillation, as well as the character and intensity degree. Thus, in seismic zoning, besides all other elements which are usually taken into consideration, it is also necessary to consider the following: orientation and dimension of the focus, and the kind and size of the motion in it. Then the spatial relationship between the motion focus and the area on the surface of the Earth under consideration could be determined, along with the dynamic characteristics of the seismic oscillations, and also the volume of the released energy, as well as the intensity degree of expected motion in future, which, as it can be seen from some examples, can reach almost the same maximal epicentral value not only in the epicentral area but also outside it.
of the expected maximum magnitude (Mmax) in future earthquakes is one of the most
important problems in seismic zoning of an area. On the example of the
methods have been used for the first time for 4 seismoactive
zones on the
analysis of seismic data of the Andaman-Nicobar
Island region that lies between 4°-16°N and 90°-98°E has been made for the 1900
– 1982 period. A seismicity map has been
prepared for the aforesaid period. The major features of the seismicity of the region are well seen from this map. It
shows a well-defined pattern almost parallel to the structural trend of the
basin. The b values as determined
from the earthquake frequency-magnitude relationship of Gutenberg and Richter
are found to be in good agreement with the result obtained in northeast
The modern seismical preventive, representing a rapidly developing field of research activities, is based mostly on data related to the locations of sources of seismic energy that pose a threat to given part of Earth’s surface, as well as those related to their capacities in respect of stored seismic energy.
Such investigations are of particular importance in the areas threatened by earthquake of tectonic origin, and these are of both the basic and applied nature. According to relations among their superficial and deeper geological structural features, strains and stresses, recent tectonic displacements and seismic activities, to the seismotectonical investigations are able to determine the seismogene structures, as well as to predict the positions and capacities of foci of possible earthquakes that can threaten a given area. Such data then represent the important criteria in determining the parameters in planning of buildings and other objects in earthquake prone areas.
Seismotectonics is relatively new science, based on and resulting from the geological, geophysical and seismical studies and investigations. The cumulative effects of these results, as well as their quality, were mainly responsible for development of seismo-tectonics. Its development has also been influenced by the construction industry, particularly when planning high dams, nuclear power plaints, and other objects where the extreme safety is requested. This cannot be done without the data obtained by seismotectonic investigations.
definition of function of seismic energy attenuation has important influence on
the seismic design parameters. Empirical attenuation functions of acceleration
or the intensity of earthquakes, which are often applied in