Vladimír Schenk

Seismotectonic model for the earthquake swarm of 1985–1986 in the Vogtland/West Bohemia focal area

Abstract After decades of minor seismic activity an intensive earthquake swarm occurred in 1985–1986 with a maximum activity in December 1985 and January 1986, in the well-known narrow focal zone of swarm quakes in the border region of the G.D.R. and Czechoslovakia. Local seismic networks recorded more than 8000 events during this swarm, the strongest local magnitude being 4.6. Nearly all of these swarm events were located within a relatively small focal volume 3.5 km in length, 1.5 km in width, and at depths of 6–8 km. Fault-plane solutions could be determined for 17 of the strongest events. They provided the basis for seismotectonic modelling in connection with (1) detailed tectonic data (including faults indicating conditions at the seismogenic depths, and recent active faults), (2) crustal stress data, and (3) studies on recent horizontal movements of crustal micro-blocks. According to detailed local micro-earthquake monitoring since 1962, all epicentral areas of swarms are aligned along the N153°E striking Marianske Lazně fault (MLf), which trends approximately in the azimuth of maximum compressive stress. The MLf is intersected by a bundle of recent active, lamellar N-S to NNE-SSW fault elements. The fault-plane solutions of 14 of the events studied show strikes in this direction. The others strike along the MLf. Tectonic evidence for the conjugate planes is lacking. Both the MLf and the N-S fault elements show a tendency to dextral creep according to neotectonics and recent horizontal crustal movements, whereas a generally sinistral elastic rebound has been derived for the focal process of the swarm. This reflects alternating block movements which could also be deduced from repeated geodetic measurements. Probably, the MLf system provides a suitable setting for the foci only, whereas the faulting process itself occurs mainly on secondary faults within the system. Moreover, a splay-structure along the MLf, immediately south of the 1985–1986 epicentral area and connected with a right-stepping offset along a N-S fault element, substantiates the proneness to the occurrence of swarm-like seismic activity.

Vulnerability and the MSK scale

Abstract Vulnerability is defined as the degree of damage (or loss) due to shaking of a given intensity. The text of the MSK macroseismic scale describing individual intensity grades determines vulnerability functions for three main categories of structures. The resulting curves are compared with the few existing examples of vulnerability curves derived for specific categories of buildings in the Caucasus and in California.

Seismic hazard estimate for a low seismicity region — Example of Bohemia

The contribution reviews basic concepts of earthquake hazard assessment for sites of nuclear power plants. Taking into account the delineation of earthquake source regions, intensity-frequency relations, upper intensity thresholdsImax and intensity attenuation curves, we determine the seismic hazard for a site in south Bohemia and calculated the quantities defining the seismic hazard, i.e. return period in years, probability of exceedance for different intensities and different periods of interest. The adopted procedure has some limitations due to the poor definition of seismogenic zones (boundaries,N(I),Imax) and lack of strong motion observations in Central Europe.

Return periods of earthquakes and trends of seismic activity

SummaryThe earthquake activity in Europe is investigated in the paper using return periods of earthquakes in fifteen European seismic regions. The variations of return periods are compared with the fundamental structure of Europe and with the observed migrations of epicentres. The probabilities of occurrence of earthquakes and their return periods are obtained by applying the theory of largest values to the data in KárníksCatalogue of European Earthquakes 1901–1967.

Relation between macroseismic intensity and instrumental parameters of strong motions — A statistical approach

One hundred and twenty-eight strong ground motion CALTECH (Earthquakes in the U.S.A., 1940–1971) records of five Californian earthquakes, recorded at ground level and in basements, for which the modified Mercalli macroseismic intensities are known, were statistically processed to calculate 165 wave parameters. Correlation of the peak values of particle acceleration, velocity and displacement, energy, impulse and root-mean-square amplitude of the vibrations, durations of vibrations for certain levels of the peak amplitude, and spectral energies of 10 frequency windows with macroseismic intensity are discussed from the viewpoint of classification of ground-motion records.

Seismotectonic model of the upper part of the Earth's crust of Czechoslovakia

РезюмеКорреляцuя месm вознuкновенuя землеmрясенuŭ нa mеррumорuu Чехословaкuu u ее окресmносmu с ¶rt;aннымu nо неоmекmонuке,геоморфологuu, современным ¶rt;вuженuям земноŭ коры, космuческоŭ съемке nоверхносmu Землu uгеофuзuческuм nолям nозволuлa вы¶rt;елumь основные сmрукmырные блокu в верхнеŭ чaсmu земноŭ коры. Нa зонaх меж¶rt;у эmuмu блокaмu нaблю¶rt;aеmся возрaсmaнuе ¶rt;олговременных ¶rt;вuженuŭ, особенно в неоu¶rt;ном nерuо¶rt;е. Поэmому nре¶rt;лaгaемaя сеŭсмоmекmонuческaя мо¶rt;ель верхнеŭ чaсmu земноŭ коры основaнa нa современных знaнuяхгео¶rt;uнaмuческuх nроцессов, nроuсхо¶rt;ящuх нa uзучaемоŭ mеррumорuu, u нa uх связu с nо¶rt;вuжнымu зонaмu.SummaryA correlation of the earthquake occurrence on the territory of Czechoslovakia and in its close neighbourhood with the data on the neotectonic and geomorphological development of the respective area, the recent movements of the Earths crust, the courses of photolineations and on the geophysical fields enabled the fundamental structural blocks in the upper part of the Earths crust to be singled out. The contact zones established between the above blocks exhibit increased long-term movement tendencies particularly in the Neoid period. A seismotectonic model of the upper part of the Earths crust of Czechoslovakia, compiled with the use of the data mentioned above, is described.

Seismotectonic scheme of Central and Eastern Europe

SummaryThe distribution of earthquake foci in the crust and the upper mantle indicates the position of mobile zones. Comparing epicentral maps of Central and Eastern Europe, known tectonic lines, results of deep seismic sounding and gravimetric survey enables a scheme of potential seismogenic zones, which correspond to active fault zones separating plates and blocks in the area, to be compiled. The level of earthquake activity varies along the investigated boundaries and can be considered as a measure of the intensity of the present geodynamic processes.

Achievements and probable trends in seismic hazard assessment

Abstract The seismic hazard can be expressed in different ways: from simple observed macroseismic fields, to seismostatistical calculations for analyzing earthquake occurrences in time and space and assessing their dynamic effects in a certain site or region, to sophisticated seismogeological approaches for evaluating the maximum expected earthquake effects on the Earths surface. The advantages and shortcomings of each method, means of delineating source regions, testing the quality of input data, processing such data to suit the chosen method of hazard assessment, and estimates of the maximum expected earthquake magnitude and of the attenuation relationships as well as the extent of the errors in all these factors will be presented.

Seismic hazard computations for regions with low earthquake activity — A case study for the Belgium, The Netherlands and NW Germany area

The algorithms to evaluate seismic hazard, used and/or developed by five teams participating in the TERESA project, applied to the low seismicity area ‘Belgium, The Netherlands and NW Germany’ are compared. The main differences in the results can be explained by the majority criterion of Egozcue et al. (1989), the differences in the upper bound and zonification and, in some cases, by a higher attenuation.

Frequency content of stress waves in the nearest zone of a spherical explosive source in gravel sandy soil

ZusammenfassungBei Verfolgung der Entstehung und Formierung der durch eine explosive Kugelquelle erregten Druckwellen steht die Frage ihres Frequenzgehalts im Vordergrund. Der Frequenzgehalt dieser Wellen wurde durch die Abhängigkeit ausgedrückt (2), die die Änderungen der relativen Breite des Amplitudenspektrums (1) vom Gewicht und von der Entfernung der Quelle angibt. Aus(2) erfolgt, dass der Frequenzgehalt der Druckwellen mit wachsender Entfernung und Grösse der Ladung exponential sinkt, wobei die Steilheit dieses Abfalls für höhere Grössen der Ladung kleiner ist. Das Herabsetzen des Frequenzgehalts dieser Wellen verursacht, dass die maximate spektral Dichte in grösseren Entfernungen von der Quelle markanter wird.