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

Abstract

[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,

Seismically triggered anomalies in the isotope signatures of mantle‐derived gases detected at degassing sites along two neighboring faults in NW Bohemia, central Europe

“…Further detailed studies by Hrubcová et al . [] supported the interpretation of a laminated Moho structure, with a Moho transition zone that varied between 2 and 4 km in thickness at depths ranging from 27 to 31.5 km. Seismic data from the BOHEMA experiment, together with data from previous seismic experiments, have been used to investigate the structure of the upper mantle beneath NW Bohemia [ Heuer et al ., ] and confirmed updoming in the Moho [ Geissler et al ., ].…”

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

“…It can also be combined with PS conversions detected on horizontal components. However, in this case, the horizontal recordings must be rotated according to their radiation patterns and source-receiver geometry (as in Hrubcová et al [2013]). Another option is to perform the analysis of the total vector which also includes horizontal components.…”

“…A similar approach has been applied by Hrubcová et al . [] who studied topography of the Moho discontinuity using microseismic data.…”

Moment Tensor Inversion Based on the Principal Component Analysis of Waveforms: Method and Application to Microearthquakes in West Bohemia, Czech Republic

“…The West Bohemia Swarm Area The West Bohemia region is situated in the western part of the Bohemian Massif at the contact of three Variscan structural units: (1) Saxothuringian, (2) Teplá-Barrandian, and (3) Moldanubian (Babuška et al, 2007). The triple junction of the units is characterized by thinning of the crust with depth of Moho ranging from 28 to 32 km (Hrubcová et al, 2013).…”