[1] In West Bohemia, central Europe, during October 2008 an earthquake swarm of 25,000 shocks with a maximum event of M L $ 3.7-3.8 occurred at depths of 7-11 km. In 2007, annual GPS campaigns were launched. During the co-seismic phase, displacements of a few centimeters were detected at GPS sites. Maximum displacement was revealed at the KOPA site, which subsided by 167 mm. The epicentral area is covered by eluvium of 4-10 m thick, and is located in undulating pastures and well-forested valleys where visible surface soil effects could not be observed. To test possible fault manifestations, rough geomorphologic, geoelectric, and geochemical surveys were performed. GPS and seismic data, with geologic materials, were used to build a forward model for surface displacements, crustal deformations, and shear and normal stress fields. The fields enabled us to better determine crustal deformations and stresses that appeared within the seismic cycle, during the pre-, co-, and post-seismic phases. During the co-seismic phase, modeled fault motions along N-S faults located within the epicentral zone reached 0.6-1 mm/day. Possible structural block rotations were comprised of these motions. A dominant role for stress accumulation, release, and relaxation was assigned to the Mariánské Lázně fault zone and the Nový Kostel zone. Strain loads slowly, and when local PT conditions with an action of deep magmatic fluids reach instability, the strain is released and stress balancing occurs. The process leads to the reversible motions known for silent earthquakes. A forward crustal deformation model for West Bohemia is also presented within.

In West Bohemia in the period of 2003−2005 five permanent GPS stations were established to detect local movement trends. Their mutual position changes were determined from time series of GPS observations and were associated with seismic, gravity, and geo-scientific data related to the geodynamics of the West Bohemian region. Knowledge of local physical processes based on spatial and time earthquake occurrences, focal mechanisms of main events, stress and strain fields set up a tool for recent seismotectonic analyses. The permanent GPS measurements bring independent effective phenomenon, direct monitoring of site movements. The movements detected by our GPS stations evidenced WSW-ENE extension with subsiding trends in the western part of the Cheb Basin and the Smrčiny Mts. Besides, there were monitored dextral movements along the Mariánské Lázně tectonic fault zone (MLF). A comparison of results with previous data formed a presumption that an antithetic stress pattern has to exist inside the inner part of the MLF tectonic zone. This antithetic stress can explain the coexistence of dextral and sinistral movements on individual tectonic elements in the West Bohemian area.

Grtinthal, G., Schenk, V., Zeman, A. and Schenkova, Z., 1990. Seismotectonic model for the earthquake swarm of [1985][1986] in the Vogtland/West Bohemia focal area. Tectonophysics, 174: 369-383.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 N153OE striking Marianske Lbnl! 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.

Macroseismic intensity, a useful measure of earthquake effects, is still applied in a wide range of seismological applications like seismic hazard assessments, attenuation relationships, etc. Isoseismals represent the spatial distribution of macroseismic intensities, and their shapes depend on source properties, lithosphere structures, tectonic line orientations, site geology, and topography. The applications ask for both the higher number of isoseismal maps, and their standardization and homogenization. The point kriging gridding method for an automatic computer drawing of isoseismal maps was delivered. Smoothing rates and numerical parameters used in the kriging algorithm were tested on macroseismic data of Greek earthquakes representing different tectonic and geomorphological regimes. The optimum kriging default option was defined. Its application for four Greek earthquakes is presented and discussed from the viewpoint of a broad use in recent macroseismology.

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