Structural Preconditions of West Bohemia Earthquake Swarms

Novotný, Miroslav; Špičák, Aleš; Weinlich, F. H.

doi:10.1007/s10712-013-9239-x

Cited by 4 publications

(2 citation statements)

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“…Many geophysical investigations were performed using different techniques to derive structural constraints on the proposed mechanisms for the unusual earthquake swarm behaviour. Overviews of such studies are given, for example, in Novotný et al (2013) and Fischer et al (2014). The method of local earthquake tomography (LET) provides information on the Vp and Vp/Vs crustal structure within the context of the seismicity distribution.…”

Section: Introductionmentioning

confidence: 99%

Seismic tomography reveals a mid-crustal intrusive body, fluid pathways and their relation to the earthquake swarms in West Bohemia/Vogtland

Mousavi¹,

Bauer

Korn³

et al. 2015

Geophys. J. Int.

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The region of West Bohemia/Vogtland in the Czech-German border area is well known for the repeated occurrence of earthquake swarms, CO 2 emanations and mofette fields. We present a local earthquake tomography study undertaken to image the Vp and Vp/Vs structure in the broader area of earthquake swarm activity. In comparison with previous investigations, more details of the near-surface geology, potential fluid pathways and features around and below the swarm focal zone could be revealed. In the uppermost crust, for the first time the Cheb basin and the Bublák/Hartoušov mofette fields were imaged as distinct anomalies of Vp and Vp/Vs. The well-pronounced low-Vp anomaly of the Cheb basin is not continuing into the Eger rift indicating a particular role of the basin within the rift system. A steep channel of increased Vp/Vs is interpreted as the pathway for fluids ascending from the earthquake swarm focal zone up to the Bublák/Hartoušov mofette fields. As a new feature, a mid-crustal body of high Vp and increased Vp/Vs is revealed just below and north of the earthquake swarm focal zone. It may represent a solidified intrusive body which emplaced prior or during the formation of the rift system. We speculate that enhanced fluid flow into the focal zone and triggering of earthquakes could be driven by the presence of the intrusive body if cooling is not fully completed. We consider the assumed intrusive structure as a heterogeneity leading to higher stress particularly at the junction of the rift system with the basin and prominent fault structures. This may additionally contribute to the triggering of earthquakes.

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Section: Introductionmentioning

confidence: 99%

Seismic tomography reveals a mid-crustal intrusive body, fluid pathways and their relation to the earthquake swarms in West Bohemia/Vogtland

Mousavi¹,

Bauer

Korn³

et al. 2015

Geophys. J. Int.

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“…The ascending mantle-derived supercritical CO 2 can transfer heat in fault systems from greater depths, as observed in CO 2 production wells (Paterson et al 2008) what would shift the border of the single-phase CO 2 -H 2 O system in lower depths. This may explain the observed upward migration of seismic activity during some earthquake swarms (Fischer et al 2010;Novotn y et al 2013) triggered by assumed fluid invasion.…”

Section: The Co 2 Bearing Fluidsmentioning

confidence: 85%

Carbon dioxide controlled earthquake distribution pattern in the NW Bohemian swarm earthquake region, western Eger Rift, Czech Republic – gas migration in the crystalline basement

Weinlich

2013

Geofluids

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The ascent of magmatic carbon dioxide in the western Eger (Ohře) Rift is interlinked with the fault systems of the Variscian basement. In the Cheb Basin, the minimum CO2 flux is about 160 m3 h−1, with a diminishing trend towards the north and ceasing in the main epicentral area of the Northwest Bohemian swarm earthquakes. The ascending CO2 forms Ca‐Mg‐HCO3 type waters by leaching of cations from the fault planes and creates clay minerals, such as kaolinite, as alteration products on affected fault planes. These mineral reactions result in fault weakness and in hydraulically interconnected fault network. This leads to a decrease in the friction coefficient of the Coulomb failure stress (CFS) and to fault creep as stress build‐up cannot occur in the weak segments. At the transition zone in the north of the Cheb Basin, between areas of weak, fluid conductive faults and areas of locked faults with frictional strength, fluid pressure can increase resulting in stress build‐up. This can trigger strike‐slip swarm earthquakes. Fault creep or movements in weak segments may support a stress build‐up in the transition area by transmitting fluid pressure pulses. Additionally to fluid‐driven triggering models, it is important to consider that fluids ascending along faults are CO2‐supersaturated thus intensifying the effect of fluid flow. The enforced flow of CO2‐supersaturated fluids in the transitional zone from high to low permeability segments through narrowings triggers gas exsolution and may generate pressure fluctuations. Phase separation starts according to the phase behaviour of CO2‐H2O systems in the seismically active depths of NW Bohemia and may explain the vertical distribution of the seismicity. Changes in the size of the fluid transport channels in the fault systems caused, or superimposed, by fault movements, can produce fluid pressure increases or pulses, which are the precondition for triggering fluid‐induced swarm earthquakes.

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Depth-Recursive Tomography of the Bohemian Massif at the CEL09 Transect—Part B: Interpretation

Novotný

2011

Surv Geophys

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In the accompanying paper (Part A), depth-recursive tomography was applied to the CEL09 refraction data. A deblurred P-wave velocity image was obtained down to a depth of 20 km. This paper (Part B) is devoted to the interpretation of the upper-and middle-crustal structures of the Bohemian Massif imaged in the CEL09 section. Because of inherent ambiguity of the refraction method in imaging low-velocity zones, other wellknown results based on other geophysical data sets are also used to independently verify the interpreted velocity features. Comparison with the density and velocity models previously obtained indicates that the presented P-wave velocity image has superior resolution revealing or verifying a number of geological features. The prominent lateral velocity changes encountered in the CEL09 pattern across the imaged crustal section were used to delineate the main terranes and deep regional fault zones such as the Krušné hory Fault, the SW continuation of the Litoměřice Fault Zone, the West and Central Bohemian Shear Zones, the Blanice-Rodl Fault, the Přibyslav-Vitis Fault and the Boskovice-Diendorf Fault. The 450-km-long CEL09 transect reveals seven major deeply rooted high-velocity (HV) anomalies identified as Variscan massifs intruded near or within these deep fault zones. They form buried ridges mostly parallel to the SW-NE trending Variscan strike. Their discovery allows new insights into a number of phenomena such as the West Bohemian earthquake swarms, the Saxothuringian paradox, the character of the SaxothuringianBarrandian contact zone, the detachment surface due to the slab of the Saxothuringian crust subducting beneath the Teplá-Barrandian zone in the Devonian, the depth extent of the Mariánské-Lázně Complex (MLC) as an equivalent unit of the Zone Erbendorf-Vohenstrauss (ZEV), the subsidence of the Barrandian syncline, the root zones of the Central and South Bohemian Plutons, the accretionary wedge formed along the Moravo-Moldanubian suture and its link with the Gföhl terrane, the Carpathian foreland relief and the subsidence observed in the Vienna Basin.Keywords Depth-recursive tomography on grid Á P-wave velocity image Á CEL09 refraction profile Á 9HR reflection profile Á Bohemian Massif Á Saxothuringian Á Mariánské M. Novotný (

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Structural Preconditions of West Bohemia Earthquake Swarms

Cited by 4 publications

References 82 publications

Seismic tomography reveals a mid-crustal intrusive body, fluid pathways and their relation to the earthquake swarms in West Bohemia/Vogtland

Seismic tomography reveals a mid-crustal intrusive body, fluid pathways and their relation to the earthquake swarms in West Bohemia/Vogtland

Carbon dioxide controlled earthquake distribution pattern in the NW Bohemian swarm earthquake region, western Eger Rift, Czech Republic – gas migration in the crystalline basement

Depth-Recursive Tomography of the Bohemian Massif at the CEL09 Transect—Part B: Interpretation

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