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  • Articles  (13)
  • earthquake swarms  (13)
  • Architecture, Civil Engineering, Surveying  (13)
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  • Articles  (13)
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  • 1
    Electronic Resource
    Electronic Resource
    Analysis of State of Stress During The 1997 Earthquake Swarm In Western Bohemia (2000)
    Springer
    Studia geophysica et geodaetica 44 (2000), S. 272-291 
    Details
    ISSN: 1573-1626
    Keywords: West Bohemia ; earthquake swarms ; stress analysis ; Gephart and Forsyth method ; fault plane discrimination
    Source: Springer Online Journal Archives 1860-2000
    Topics: Architecture, Civil Engineering, Surveying , Geosciences , Physics
    Notes: Abstract Focal mechanisms of 70 events of the January 1997 earthquake swarm were analysed using the Gephart and Forsyth method to determine the state of stress in the West Bohemia/Vogtland region and to reveal possible stress variations during the swarm activity. The method was applied to the whole set of 70 focal mechanisms and to several subsets distinguishing magnitudes of events and the spatial and temporal distribution of the swarm. The three representative stress models A (σ 1 ,A: 0/45 (az/dip), σ 2 A: 134/35, σ 3 A: 243/25), B (σ 1 ,B: 162/38, σ 2 B: 263/14, σ 3 B: 10/49), and C (σ 1 C: 135/30, σ 2 C: 1/50, σ 3 C: 239/23) which could characterise the state of stress in the region were found. Model C can be considered to be the most probable stress model because of its consistency with the European stress field. The results of the stress analysis applied to the individual subsets of focal mechanisms indicate that the state of stress was more uniform during the first phase of the swarm. To distinguish between the fault plane and the auxiliary plane of fault plane solutions a statistical approach was used. The results showed that the fault planes striking NW-SE and dipping 45° to NE were activated during the swarm.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/A:1022171027896
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  • 2
    Electronic Resource
    Electronic Resource
    Subsurface Temperature Changes Due to the Crustal Magmatic Activity – Numerical Simulation (2000)
    Springer
    Studia geophysica et geodaetica 44 (2000), S. 327-335 
    Details
    ISSN: 1573-1626
    Keywords: magma intrusions ; crustal temperatures ; earthquake swarms ; Bohemian Massif
    Source: Springer Online Journal Archives 1860-2000
    Topics: Architecture, Civil Engineering, Surveying , Geosciences , Physics
    Notes: Abstract Geothermal aspects of the hypothesis, relating the earthquake swarms in the West Bohemia/Vogtland seismoactive region to magmatic activity, are addressed. A simple 1-D geothermal model of the crust was used to assess the upper limit of the subsurface heating caused by magma intrusion at the assumed focal depth of 9 km. We simulated the process by solving the transient heat conduction equation numerically, considering the heat of magma crystallization to be gradually released in the temperature interval 1100°C to 900°C. The temperature field prior to the intrusion was in steady-state with a surface temperature of 10°C and heat flow of 80 mWm −2 , the temperature at the 9 km depth was 270°C. The results suggest that the temperature and heat flow in the uppermost 1 km of the crust begin to grow 100 ka after the intrusion emplacement only, and that the amplitudes of the changes for the realistic lateral extent (a few kilometres) of the intrusion are very small. It was also found that the rate of magma solidification depends strongly on the thickness of the intrusion. It takes about 100 years for a 50 m thick sill to cool down from 1100°C to 600°C, which value represents the lower limit of the solidus temperature. The same cooling takes only 60 days if the sill is 2 m thick. If the nature of the strongly reflected boundaries, interpreted from the January 1997 Nový Kostel seismograms, is connected with the fresh emplacement of magma, the calculated cooling rates have a predictive potential for the temporal changes of the waveforms.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/A:1022127312875
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  • 3
    Electronic Resource
    Electronic Resource
    Magma Intrusions and Earthquake Swarm Occurrence in the Western Part of the Bohemian Massif (1999)
    Springer
    Studia geophysica et geodaetica 43 (1999), S. 87-106 
    Details
    ISSN: 1573-1626
    Keywords: earthquake swarms ; magma intrusions ; fluids ; Bohemian Massif ; induced seismicity ; WEBNET ; KTB ; 9HR
    Source: Springer Online Journal Archives 1860-2000
    Topics: Architecture, Civil Engineering, Surveying , Geosciences , Physics
    Notes: Abstract We are proposing a hypothesis that earthquake swarms in the West Bohemia/Vogtland seismoactive region are generated by magmatic activity currently transported to the upper crustal layers. We assume that the injection of magma and/or related fluids and gases causes hydraulic fracturing which is manifested as an earthquake swarm at the surface. Our statements are supported by three spheres of evidence coming from the western part of the Bohemian Massif: characteristic manifestations of recent geodynamic activity, the information from the neighbouring KTB deep drilling project and from the 9HR seismic reflection profile, and the detailed analysis of local seismological data. (1) Recent manifestations of geodynamic activity include Quaternary volcanism, rich CO 2 emissions, anomalies of mantle-derived 3 He, mineral springs, moffets, etc. (2) The fluid injection experiment in the neighbouring KTB deep borehole at a depth of 9 km induced hundreds of micro-earthquakes. This indicates that the Earth's crust is near frictional failure in the western part of the Bohemian Massif and an addition of a small amount of energy to the tectonic stress is enough to induce an earthquake. Some pronounced reflections in the closely passing 9HR seismic reflection profile are interpreted as being caused by recent magmatic sills in the crust. (3) The local broadband seismological network WEBNET provides high quality data that enable precise localization of seismic events. The events of the January 1997 earthquake swarm are confined to an extremely narrow volume at depths of about 9 km. Their seismograms display pronounced reflections of P- and S-waves in the upper crust. The analysis of the process of faulting has disclosed a considerable variability of the source mechanism during the swarm. We conclude that the mechanism of intraplate earthquake swarms generated by magma intrusions is similar to that of induced seismicity. As the recent tectonic processes and manifestations of geodynamic activity are similar in European areas with repeated earthquake swarm occurrence (Bohemian Massif, French Massif Central, Rhine Graben), we assume that magma intrusions and related fluid and gas release at depths of about 10 km are the universal cause of intraplate earthquake swarm generation
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/A:1023366210017
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  • 4
    Electronic Resource
    Electronic Resource
    The Western Bohemia/Vogtland Region in the Light of the Webnet Network (2000)
    Springer
    Studia geophysica et geodaetica 44 (2000), S. 107-125 
    Details
    ISSN: 1573-1626
    Keywords: West Bohemia ; earthquake swarms ; local seismic network ; local magnitude ; local earthquake waveform
    Source: Springer Online Journal Archives 1860-2000
    Topics: Architecture, Civil Engineering, Surveying , Geosciences , Physics
    Notes: Abstract The local network of digital seismic stations WEBNET monitors the seismic activitv of practically the whole region of Western Bohemia/Vogtland swarms. The network consists of ten short-period stations and one very broadband station. The paper describes the configuration of the network, instrumental equipment and the basic parameters of the stations. The method of and formula for computing the local magnitudes from the WEBNET and KRASLICE seismograms are also given. Based on continuous WEBNET observations in the period 1995-1999, we were able to improve the model of temporal and spatial energy release in the region, the principal characteristics of which are summarised in the paper. Apart from direct P and S waves, the WEBNET seismograms also contain other significant P- and S-type waves, provisionally interpreted as reflected PxP, SxS and SxP waves. The fundamental characteristics of these waves are given in the paper, and tentative mechanisms of their origination are discussed. The large residua in the travel times of the P and S waves, and the discrepancies in the seismograms recorded at stations located east of the principal focal zone are pointed out.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/A:1022198406514
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  • 5
    Electronic Resource
    Electronic Resource
    Refined Locations of The Swarm Earthquakes In The Nový Kostel Focal Zone and Spatial Distribution of The January 1997 Swarm In Western Bohemia, Czech Republic (2000)
    Springer
    Studia geophysica et geodaetica 44 (2000), S. 210-226 
    Details
    ISSN: 1573-1626
    Keywords: earthquake swarms ; cluster of foci ; relative location ; cluster analysis ; multiplet events
    Source: Springer Online Journal Archives 1860-2000
    Topics: Architecture, Civil Engineering, Surveying , Geosciences , Physics
    Notes: Abstract In order to improve the accuracy of the spatial distribution of earthquake foci in the principal Novy Kostel focal zone, refined focal locations of about 1500 micro-earthquakes of the 1991 – 1997 period were determined using the relative Master-Event location method. To estimate the reduction in the scatter of located hypocentres, the results were compared with those obtained by routinely used FASTHYPO method and cluster analysis (the nearest-neighbour method) was applied to the located foci to evaluate the spatial distribution of the foci. Based on the results of refined location and of the cluster analysis, a concept of seismic energy release in space and time in the main focal zone was developed. Especially the January 1997 earthquake swarm was studied in detail: 946 events were located with the Master-Event location method, and the dimensions and geometry of focal clusters were determined. Type analysis was applied to waveforms to divide approximately 800 located events into eight multiplet groups to each of which a characteristic source mechanism was assigned. The spatial distribution of the foci as well as of the eight types of source mechanisms was revealed in this way and also the planes fitting the clusters of foci with two predominant source mechanisms were determined fairly well.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/A:1022162826079
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  • 6
    Electronic Resource
    Electronic Resource
    A preliminary seismic model for the region of the west-Bohemian earthquake swarms (1996)
    Springer
    Studia geophysica et geodaetica 40 (1996), S. 353-366 
    Details
    ISSN: 1573-1626
    Keywords: crustal structure ; Western Bohemia ; Vogtland ; earthquake swarms
    Source: Springer Online Journal Archives 1860-2000
    Topics: Architecture, Civil Engineering, Surveying , Geosciences , Physics
    Notes: Summary A layered model of the crustal and upper mantle structure for the region of the West-Bohemian earthquake swarms is proposed. This model represents a compilation of the results of deep seismic soundings, surface-wave investigations, and some local seismic measurements in the western regions of the Bohemian Massif.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02300764
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  • 7
    Electronic Resource
    Electronic Resource
    Homogeneous Velocity Models of The West Bohemian Swarm Region Obtained By Grid Search (2000)
    Springer
    Studia geophysica et geodaetica 44 (2000), S. 158-174 
    Details
    ISSN: 1573-1626
    Keywords: West Bohemia ; earthquake swarms ; location ; grid search ; homogeneous velocity models
    Source: Springer Online Journal Archives 1860-2000
    Topics: Architecture, Civil Engineering, Surveying , Geosciences , Physics
    Notes: Abstract West Bohemian earthquake swarms are used to determine the parameters of simple homogeneous velocity models of the individual subregions of the given area, based on a group of earthquakes that occurred in these subregions. The grid search method is used for location. Models yielding the minimum sum of squares of the travel-time residua in locating the whole group of earthquakes in the given subregion are considered suitable. Relocation obtained by grid search is compared with that obtained by the FASTHYPO method. The computations indicate that the subregions under consideration can be, from the point of view of earthquake location, sufficiently represented by homogeneous models, but the models differ for the data from different subregions. The velocities of these models are given. The models under consideration are compared with some of the previously published 1-D models of the broader region of Western Bohemia.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/A:1022154624261
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  • 8
    Electronic Resource
    Electronic Resource
    Repeated Geodetic Measurements in the West Bohemia Seismoactive Region: Period 1993 - 1996 (1997)
    Springer
    Studia geophysica et geodaetica 41 (1997), S. 319-328 
    Details
    ISSN: 1573-1626
    Keywords: earthquake swarms ; surface deformations ; GPS ; precise levelling
    Source: Springer Online Journal Archives 1860-2000
    Topics: Architecture, Civil Engineering, Surveying , Geosciences , Physics
    Notes: Abstract The western part of the Bohemian Massif is characterized by repeated occurrences of intraplate earthquake swarms. To study surface deformations of this anomalous region, a network covering about 2000 square kilometres for repeated geodetic measurements was established in 1993 - 1994. The positions of the individual points of the network were carefully picked with respect to local tectonic structure and earthquake foci distribution. GPS and precise levelling measurements were performed 1-2 times a year. The GPS data were processed by Bernese GPS software. No tendency to any displacement - either horizontal or vertical - of geological blocks was derived from the geodetic data for the period 1993 - 96. Only displacements of less than 5 mm/year in average could occur in the whole region in that period; larger displacements would have been revealed by our measurements.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/A:1023355300199
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  • 9
    Electronic Resource
    Electronic Resource
    Focal Mechanisms and Stress Field in The Region Vogtland/Western Bohemia (2000)
    Springer
    Studia geophysica et geodaetica 44 (2000), S. 126-141 
    Details
    ISSN: 1573-1626
    Keywords: Vogtland/Western Bohemia ; earthquake swarms ; focal mechanismsm ; stress field
    Source: Springer Online Journal Archives 1860-2000
    Topics: Architecture, Civil Engineering, Surveying , Geosciences , Physics
    Notes: Abstract We calculated focal mechanisms for 30 of the strongest events (1.5 ≤ M L ≤ 3.3) in distinct subregions of Vogtland/Western Bohemia between 1990 and 1998. Our investigations are concerned with events of the swarms near Bad Elster (1991), Haingrün (1991), Nový Kostel (1994 and 1997) and Zwickau (1998), two events from a group of earthquakes near Klingenthal (1997) and eight single events. Seismograms were provided by the digital station networks of the Geophysical Observatory of the University of Munich, the Technical University of Freiberg, the Academy of Sciences of the Czech Republic in Prague, the Masaryk University in Brno and some nearby stations of the German Regional Seismic Network (GRSN). To calculate focal mechanisms two inversion methods were applied. The inferred focal mechanisms do not show a simple, uniform pattern of seismic dislocation. All possible dislocation types – strike-slip, normal and thrust faulting - are represented. The prevailing mechanisms are normal and strike-slip faulting. Considerable differences in the fault plane solutions are noted for the individual subregions as well as in some cases among the individual events of a single swarm. For the Nový Kostel area we succeeded to resolve a change in the orientations of the nodal planes for the two successive swarms of December 1994 and January 1997. Besides this we also observe a change in the mechanisms, namely from strike-slip and normal faulting (December 1994) to strike-slip and thrust faulting (January 1997). Based on the inferred focal mechanisms the stress field was estimated. It turned out, that the dominating stress field in the region Vogtland/Western Bohemia does not substantially differ from the known stress field of West and Central Europe, being characterized by a SE-NW direction of the maximum compressive horizontal stress. We conclude that the seismicity in the Vogtland/Western Bohemia region is not predominantly caused by an independent local stress field, but rather controlled by the dominating stress regime in Central Europe.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/A:1022150523353
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  • 10
    Electronic Resource
    Electronic Resource
    Earthquake Swarms and Accompanying Phenomena in Intraplate Regions: A Review (2000)
    Springer
    Studia geophysica et geodaetica 44 (2000), S. 89-106 
    Details
    ISSN: 1573-1626
    Keywords: earthquake swarms ; Quaternary volcanism ; fluids
    Source: Springer Online Journal Archives 1860-2000
    Topics: Architecture, Civil Engineering, Surveying , Geosciences , Physics
    Notes: Abstract The western part of the Bohemian Massif has played an exceptional role in recent geodynamic activity of the region. It is characterised by repeated occurrences of earthquake swarms and by other manifestations of deep tectonic processes (CO 2 emissions, anomalous 3 He content, mineral waters, mofettes, etc.). The purpose of this paper is to introduce some other intraplate regions with earthquake swarm occurrence (French Massif Central; Colli Albani and Vulsini Mts., central Italy; Southern Apennines, Italy; the Danville and Long Valley regions, California; central Arkansas), and with artificially induced earthquake swarms (Larderello, Italy, geothermal field; Coso, California, geothermal field; NE Bavaria, Germany, deep drilling project). Although these areas represent different tectonic environments, the manifestations of recent geodynamic and/or man-made activity are similar in many aspects. This coincidence most probably issues from a common cause of both tectonic and artificially induced earthquake swarms – intrusions/injections of fluids. Since the regions with earthquake swarm occurrence of tectonic origin are situated as a rule in the close neighbourhood of Quaternary volcanoes, the intruding fluids seem to be derived from magma recently transported to upper crustal layers.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/A:1022146422444
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