Six-component seismic sensor Rotaphone
US Patent (2020), Translational rotational movement Long Valley Caldera, Ca USA
Publication: Brokešová J., Málek J. (2020): Comparative Measurements of Local Seismic Rotations by Three Independent Methods. Sensors 2020, 20(19), 5679, DOI: 10.3390/S20195679
Publication: Brokešová J., Málek J. (2018): Small-aperture seismic array data processing using a representation of seismograms at zero-crossing points. Physics of the Earth and Planetary Interiors, 280, 53-68, DOI: 10.1016/j.pepi.2018.04.010
Surface waves analysis
Multi-component analysis of surface waves reveals that a thin shallow stiff layer excites Love-wave higher modes in a very peculiar way and that the top velocity of such higher modes is controlled by the shear-wave velocity of the deeper layers.
Joint inversion of the four considered observables: phase-velocity spectra for the Z, R and T components (this latter represents the Love waves and shows the typical higher-mode excitation described in the paper) together with the RPM (Rayleigh-wave Particle Motion) frequency-offset surface.
Publication: Dal Moro G.(2020). The magnifying effect of a thin shallow stiff layer on Love waves as revealed by multi-component analysis of surface waves. Scientific Reports 10, 9071 (2020), DOI: 10.1038/s41598-020-66070-1
Stability of Rocking Stones
The Case Study of “The Hus Pulpit” in the Central Bohemian Pluton:
Critical amplitude of input bedrock velocity might be of the order of 1-2 cm/s to 2 cm/s at the frequencies up to 10 Hz. PGV of this order can be generated by an M=7 earthquake at a distance of about 150 km. That is a typical distance of the studied stone from the nearest seismically active zones.
Geometry of "the Hus Pulpit" in the Central Bohemian Pluton
Non-linear force model: the vertical component of the total traction at the base of the stone generated by the 6 Hz harmonic horizontal displacement
Publication: Zábranová, E., Matyska, C., Stemberk, Jakub Jr. and Málek, J. Eigenoscillations and Stability of Rocking Stones: The Case Study of "The Hus Pulpit" in The Central Bohemian Pluton. Pure Appl. Geophys. (2019), DOI: 10.1007/s00024-019-02296-z
Seismic Hazard map of Bosna and Herzegovina
The map have been accepted as a part of National Annex Eurocode 8
2) PGA Seismic hazard map for 10% prob. exceedence in 50 years
a) 16% percentile; b) 50% percentile; c) mean value; d) 84% percentile
3) Probabilistic seismic hazard curves, a) Banja Luka b) Sarajevo
Publication: Ademovic, N.,Demir, V., Cvijic-Amulic, S., Malek, J., Prachar, I.,Vackar, J.: Compilation of the seismic hazard maps in Bosnia and Herzegovina. Soil Dynamics And Earthquake Engineering, 141, 106500, (2020), DOI: 10.1016/j.soildyn.2020.106500
Geomechanical model of microseismicity
during hydraulic fracturing of shale
We developed new methods for passive seismic data analyses and proposed geomechanical model of relationship between microseismicity and hydraulic fracturing of shale.
Waveform Similarity analyses, Mapping activated faults, source mechanism analyses – CO2 sequestration project – Induced Seismicity;
Complex data processing, Source mechanism analyses, Geomechanical interpretation – Hydraulic fracturing of shale project – microseismic monitoring
Publication: Staněk, F., Eisner, L. Seismicity Induced by Hydraulic Fracturing in Shales: A Bedding Plane Slip Model. Journal of Geophysical Research: Solid Earth. 2017, 122(10), 7912-7926. ISSN 2169-9313, DOI: 10.1002/2017JB014213
Velocity model of REYKJANET (Iceland)
Nine broadband stations from the REYKJANET seismic network were used to derive the seismic structure aimed at determining the Rayleigh wave phase velocity dispersion. Seismograms from 2013 to 2015 included fourteen selected earthquakes; the dispersion curves were inverted into a horizontally-layered model of the S-wave velocities of the Earth’s crust and upper mantle. A significant zone of low velocities was found at depths above 20 km.
REYKJANET - seismic network in south-east Iceland - consists from 15 stations
It is operated by GFÚ AV ČR (J. Horálek) and ÚSMH AV ČR (J. Málek) since 2013
Publication: Málek J., Brokešová J., and Novotný O., (2019). Seismic structure beneath the Reykjanes Peninsula, southwest Iceland, inferred from array-derived Rayleigh wave dispersion. Tectonophysics 753, 1 – 14, DOI: 10.1016/j.tecto.2018.12.020
Ground fissures in the Main Ethiopian Rift
We explained mechanism of origin (tectonically and lithologically triggered piping) and proposed a method to estimate risk of their opening in a particular area (measurements of seismic anisotropy)
Ground fissures in the MER, and especially their sudden opening, is one of the most significant geoohazard in the area. The fissures open in unconsolidated sediments and are long (even several kilometres), narrow (0.5 to several metres), deep (usually several meters but maximum depth measured was 60 m) and fast opening (even several hundred meters in half a year). The fissures are oriented perpendicular to the main direction of extension (parallel to the Rift).
We have found that they are connected with a specific lithology (unconsolidated volcaniclastic sediments with a low amount of clay and a large amount of silt particles. Such sediments are stable when dry but unstable when soaked during the rainy season. They are interlaid with relatively impermeable layers, usually rhyoliotic ignimbrites jointed by brittle tectonics. The water preferentially flows through the jointed parts downwards. When the flow is blocked by impermeable layer the water flows horizontally eroding the clay-poor sediments, forming pipes and eroding overlying (less consolidated) material (“inverse erosion”). Subsequently the pipe ceiling suddenly collapses (usually after a heavy rain) forming the fissure.
As the water flows preferably through the less permeable layers by joints formed by extension, the fissures are oriented perpendicular to the direction of extension. The joints with preferential orientation form a significant seismic anisotropy, which can be used to map zones endangered by piping and fissure formation. We have found that fissure zones have a significant seismic anisotropy of S-waves (20% and more) while areas not affected by fissuring have the anisotropy negligible.
Therefore, we suggest to measure seismic anisotropy to evaluate a possibility of fissure formation in a specific area.
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