Moho depth determination from waveforms of microearthquakes in the West Bohemia/Vogtland swarm area

Hrubcová, Pavla; Vavryčuk, Václav; Horálek, Josef; Boušková, Alena

doi:10.1002/jgrb.50016

Cited by 10 publications

(16 citation statements)

References 34 publications

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“…However, in this case, the horizontal recordings must be rotated according to their radiation patterns and source‐receiver geometry (as in Hrubcová et al . []). Another option is to perform the analysis of the total vector which also includes horizontal components.…”

Section: Methods Of Detection Of Shallow Discontinuities From High‐frementioning

confidence: 99%

Shallow crustal discontinuities inferred from waveforms of microearthquakes: Method and application to KTB Drill Site and West Bohemia Swarm Area

et al. 2016

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The waveforms of microearthquakes are of high frequency and complicated. They contain many phases secondarily generated at crustal interfaces and at small‐scale inhomogeneities. They are highly sensitive to focal mechanisms and thus very different for each station of local networks. However, with a large number of microearthquakes, the scattered waves present in the waveforms can serve for identifying the prominent crustal discontinuities and for determining their depth. In this paper, we develop a new approach for extracting information on crustal structure from such waveforms and apply it for determining depth and lateral variations of crustal discontinuities. We show that strong dependence of microseismic waveforms on radiation pattern requires good station coverage and knowledge of focal mechanisms of the microearthquakes. Analysis of real observations is supported by waveform modeling and by analysis of radiation patterns of scattered waves. The robustness of the inversion for depth of crustal interfaces is achieved by stacking of a large number of waveforms and by applying a grid search algorithm. The method is demonstrated on two microseismic data sets of different origin: microseismicity induced during the Continental Super‐Deep Drilling Project (KTB) 2000 fluid injection experiment and natural seismicity in the West Bohemia swarm region. High‐frequency conversions at the KTB site indicate a prominent interface at depths of 2.3–4.1 km consistent with previous interpretations. Geologically, it may represent the contact of granitoids with much faster metabasites underneath. Seismicity in West Bohemia indicates a strong‐contrast interface at depths of 3.5–6.0 km. This interface is in agreement with previous profiling and might be related to trapping of fluid emanations ascending from the mantle.

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Section: Methods Of Detection Of Shallow Discontinuities From High‐frementioning

confidence: 99%

Shallow crustal discontinuities inferred from waveforms of microearthquakes: Method and application to KTB Drill Site and West Bohemia Swarm Area

et al. 2016

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“…The West Bohemia region is situated in the western part of the Bohemian Massif at the contact of three Variscan structural units: Saxothuringian, Teplá‐Barrandian, and Moldanubian [ Babuška et al , ]. The triple junction of the units is characterized by thinning of the crust with depth of the Moho ranging from 28 km to 32 km [ Hrubcová et al , ]. The tectonic structure of the area is described by two main fault systems well expressed on the surface: the NW‐SE Mariánské Lázně fault system and the SW‐NE Ore‐Mountain fault system related to Tertiary Eger Rift opening (see Figure ).…”

Section: The West Bohemia Swarm Areamentioning

confidence: 99%

Seismological evidence of fault weakening due to erosion by fluids from observations of intraplate earthquake swarms

Vavryčuk

Hrubcová

2017

JGR Solid Earth

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The occurrence and specific properties of earthquake swarms in geothermal areas are usually attributed to a highly fractured rock and/or heterogeneous stress within the rock mass being triggered by magmatic or hydrothermal fluid intrusion. The increase of fluid pressure destabilizes fractures and causes their opening and subsequent shear‐tensile rupture. The spreading and evolution of the seismic activity are controlled by fluid flow due to diffusion in a permeable rock (fluid‐diffusion model) and/or by redistribution of Coulomb stress (intrusion model). These models, however, are not valid universally. We provide evidence that none of these models is consistent with observations of swarm earthquakes in West Bohemia, Czech Republic. Full seismic moment tensors of microearthquakes in the 2008 swarm in West Bohemia indicate that fracturing at the starting phase of the swarm was not associated with fault openings caused by pressurized fluids but rather with fault compactions. This can physically be explained by a fault‐weakening model, when the essential role in the swarm triggering is attributed to degradation of fault strength due to long‐lasting chemical and hydrothermal fluid‐rock interactions in the focal zone. Since the rock is exposed to circulating hydrothermal, CO2‐saturated fluids, the walls of fractures are weakened by dissolving and altering various minerals. The porosity of the fault gauge increases, and the fault weakens. If fault strength lowers to a critical value, the seismicity is triggered. The fractures are compacted during failure, the fault strength recovers, and a new cycle begins.

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“…We used the data from the 2008 earthquake swarm located in the NK focal zone (Horálek et al, ; Fischer et al, ) (see Figure ). The waveforms recorded at 22 WEBNET network stations were cross correlated for the P waves, rotated, aligned, and stacked following the approach of Hrubcová et al (). This enabled to extract the reflected SmS phases in the S wave coda.…”

Section: Seismic Characterization Of the Lower Crustmentioning

confidence: 99%

“…Active and passive seismic studies in the western Eger Rift indicate high P wave velocities at the base of the crust (DEKORP Research Group, ; Enderle et al, ; Hrubcová et al, ; Hrubcová & Geissler, ), sometimes with strong reflectivity or with a number of distinct reflective zones (Hrubcová et al, ; Hrubcová & Geissler, ; Tomek et al, ; Trappe & Wever, ). Lateral variations of the Moho in this area are reported by receiver function studies (Geissler et al, , ; Heuer et al, ).…”

Section: Introductionmentioning

confidence: 99%

Active Magmatic Underplating in Western Eger Rift, Central Europe

et al. 2017

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The Eger Rift is an active element of the European Cenozoic Rift System associated with intense Cenozoic intraplate alkaline volcanism and system of sedimentary basins. The intracontinental Cheb Basin at its western part displays geodynamic activity with fluid emanations, persistent seismicity, Cenozoic volcanism, and neotectonic crustal movements at the intersections of major intraplate faults. In this paper, we study detailed geometry of the crust/mantle boundary and its possible origin in the western Eger Rift. We review existing seismic and seismological studies, provide new interpretation of the reflection profile 9HR, and supplement it by new results from local seismicity. We identify significant lateral variations of the high‐velocity lower crust and relate them to the distribution and chemical status of mantle‐derived fluids and to xenolith studies from corresponding depths. New interpretation based on combined seismic and isotope study points to a local‐scale magmatic emplacement at the base of the continental crust within a new rift environment. This concept of magmatic underplating is supported by detecting two types of the lower crust: a high‐velocity lower crust with pronounced reflectivity and a high‐velocity reflection‐free lower crust. The character of the underplated material enables to differentiate timing and tectonic setting of two episodes with different times of origin of underplating events. The lower crust with high reflectivity evidences magmatic underplating west of the Eger Rift of the Late Variscan age. The reflection‐free lower crust together with a strong reflector at its top at depths of ~28–30 km forms a magma body indicating magmatic underplating of the late Cenozoic (middle and upper Miocene) to recent. Spatial and temporal relations to recent geodynamic processes suggest active magmatic underplating in the intracontinental setting.

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Moho depth determination from waveforms of microearthquakes in the West Bohemia/Vogtland swarm area

Cited by 10 publications

References 34 publications

Shallow crustal discontinuities inferred from waveforms of microearthquakes: Method and application to KTB Drill Site and West Bohemia Swarm Area

Shallow crustal discontinuities inferred from waveforms of microearthquakes: Method and application to KTB Drill Site and West Bohemia Swarm Area

Seismological evidence of fault weakening due to erosion by fluids from observations of intraplate earthquake swarms

Active Magmatic Underplating in Western Eger Rift, Central Europe

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