Detection of high-frequency tensile vibrations of a fault during shear rupturing: observations from the 2008 West Bohemia swarm

Vavryčuk, Václav

doi:10.1111/j.1365-246x.2011.05122.x

Cited by 26 publications

(17 citation statements)

References 30 publications

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“…In principle, the focal mechanisms can vary in time, for example if a fault has a complex geometry. Focal mechanisms can also depend on the frequency range of the studied waves, particularly, because of small‐scale inhomogeneities and irregularities along the fault radiating high‐frequency waves (Vavryčuk 2011b). However, the assumption of the time‐independent focal mechanism is a good approximation to study an overall mechanism in the low‐frequency range.…”

Section: Methodsmentioning

confidence: 99%

“…It is usually applied employing the point‐source approximation and assuming a time‐independent focal mechanism. The inversion is performed in the time domain (Dreger & Woods 2002; Zahradník et al 2005, 2008a,b; Sokos & Zahradník 2008; Adamová et al 2009; Hingee et al 2011) or in the frequency domain using amplitude spectra (Cesca et al 2006) or complex spectra (Cesca & Dahm 2008; Vavryčuk 2011a,b). The inversion yields the moment tensor and, as a by‐product, the common source‐time function.…”

Section: Introductionmentioning

confidence: 99%

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Moment tensor inversion of waveforms: a two-step time-frequency approach

Vavryčuk¹,

Kühn

2012

Geophysical Journal International

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SUMMARY We present a moment tensor inversion of waveforms, which is more robust and yields more stable and more accurate results than standard approaches. The inversion is performed in two steps and combines inversions in time and frequency domains. First, the inversion for the source‐time function is performed in the frequency domain using complex spectra. Second, the time‐domain inversion for the moment tensor is performed using the source‐time function calculated in the first step. In this way, we can consider a realistic, complex source‐time function and still keep the final moment tensor inversion linear. Using numerical modelling, we compare the efficiency and accuracy of the proposed approach with standard waveform inversions. We study the sensitivity of the retrieved double‐couple and non‐double‐couple components of the moment tensors to noise in the data, to inaccuracies of the location and of the velocity model, and to the type of the focal mechanism. Finally, the proposed moment tensor inversion is tested on real data observed in a complex 3‐D inhomogeneous geological environment: a production blast and a rockburst in the Pyhäsalmi ore mine, Finland.

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Section: Methodsmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Moment tensor inversion of waveforms: a two-step time-frequency approach

Vavryčuk¹,

Kühn

2012

Geophysical Journal International

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“…This fault was less active and only a small portion of events occurred along it. The maximum compressive stress in the region determined from the focal mechanisms was in a NW‐SE direction with an azimuth of 146° [ Vavryčuk , ].…”

Section: Datamentioning

confidence: 99%

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

et al. 2013

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[1] The West Bohemia/Vogtland area is known for its increased geodynamic activity with reoccurrence of intraplate earthquake swarms. Previous geophysical studies, namely active and passive seismic investigations, revealed a high velocity lower crust in this area with increased reflectivity. To refine this result and retrieve a more detailed structure of the deep crust and the Moho discontinuity, we analyzed waveforms of local microearthquakes that occurred in this area during the 2008 swarm. The waveforms of earthquakes were grouped into clusters with similar focal mechanisms, and the clusters were processed separately. We developed a new multiazimuthal approach in data processing to increase resolution of Moho phases in the waveforms. We applied the waveform cross-correlation of the P and S waves, and rotated, aligned, and stacked the seismograms to extract the Moho SmS, PmP, and PmS reflected/converted phases. These phases were inverted for laterally varying Moho depth by ray tracing and a grid search inversion algorithm. The model retrieved was verified using modeling of full waveforms computed by the discrete wave number method. The multiazimuthal approach reveals details in the velocity structure of the crust/mantle transition at each station. Instead of a single interface with a sharp velocity contrast, the inversion indicates a reflective zone at Moho depths with one or two strongly reflective interfaces, which is in agreement with the zone interpreted by previous investigations. The thickness of the zone varies from 2 to 4 km within the depth range of 27-31.5 km and is delimited by reflections from its top and bottom boundaries, sometimes with strong reflectors within the zone. The average V p /V s ratio determined from the Moho reflections and conversions is 1.73.Citation: Hrubcova´, P., V. Vavrycˇuk, A. Bousˇkova´, and J. Hora´lek (2013), Moho depth determination from waveforms of microearthquakes in the West Bohemia/Vogtland swarm area,

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“…This is also evidenced by spectra of shear and tensile components of moment rate functions for earthquakes in the West Bohemia swarm (Vavryčuk, 2011a). This is also evidenced by spectra of shear and tensile components of moment rate functions for earthquakes in the West Bohemia swarm (Vavryčuk, 2011a).…”

Section: Statistical Properties Of Frequency Dependencementioning

confidence: 66%

Frequency‐Dependent Moment Tensors of Induced Microearthquakes

Vavryčuk

Adamová

et al. 2019

Geophysical Research Letters

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Analysis of 984 induced microearthquakes from The Geysers geothermal reservoir in California reveals that the retrieved moment tensors depend on the frequency band of the inverted waveforms. The observed dependence is more significant for the percentages of the double‐couple, compensated linear vector dipole, and isotropic (ISO) components than for the focal mechanisms. The average root‐mean‐square of the moment tensors obtained in different frequency bands is correlated with spectra of ambient noise. The percentages of double‐couple and ISO components tend to decrease and increase with the upper cutoff frequency (fu), respectively. This suggests that shear rupture radiates energy preferentially in a lower frequency band and tensile rupture in a higher frequency band. Events displaying a strong increase of the ISO with fu are confined within the same depth interval as the injection points. This might be related to the strong thermoelastic effects in the vicinity of injection points that promote opening of small cracks adjacent to the main fractures.

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Detection of high-frequency tensile vibrations of a fault during shear rupturing: observations from the 2008 West Bohemia swarm

Cited by 26 publications

References 30 publications

Moment tensor inversion of waveforms: a two-step time-frequency approach

Moment tensor inversion of waveforms: a two-step time-frequency approach

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

Frequency‐Dependent Moment Tensors of Induced Microearthquakes

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