5:45 PM - 6:00 PM
[S03-2-06] Joint inversion for shallow crustal discontinuities from high-frequency waveforms of microearthquakes
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 clustered microearthquakes, the reflected/converted waves in waveforms can serve for detecting prominent discontinuities within the crust. With a dense network of sensitive seismic stations and a good azimuthal distribution, it is possible to retrieve a depth of these discontinuities and map their lateral variations. The standard microseismic monitoring is routinely investigated for source parameters; however, an analysis of shallow crustal structure is often missing.
The structure studies based on microseismic data are specific. The depth of discontinuities is modelled using several independent tools provided by refraction and reflections seismics combined with the earthquake source analysis. This includes ray tracing for calculating traveltimes of converted and/or reflected phases, analysis of focal mechanisms and radiation patterns for converted/reflected phases, full waveform modelling using discrete wavenumber method for comparing synthetics with observed data, alignment of traces and their stacking for amplifying studied phases, and grid search for the inversion. Joint interpretation of more phases converted/reflected from the same interface increases the stability of retrieved results and enhances the robustness of the inversion. A novel concept for extracting crustal structure from high-frequency waveforms of local microearthquakes is demonstrated on natural seismicity in the West Bohemia swarm region, the Czech Republic. Clustered seismicity in West Bohemia indicates a strong-contrast interface at depths of 3.5-6.0 km, which is in agreement with previous profiling and might be related to trapping of fluids ascending from the mantle.
The structure studies based on microseismic data are specific. The depth of discontinuities is modelled using several independent tools provided by refraction and reflections seismics combined with the earthquake source analysis. This includes ray tracing for calculating traveltimes of converted and/or reflected phases, analysis of focal mechanisms and radiation patterns for converted/reflected phases, full waveform modelling using discrete wavenumber method for comparing synthetics with observed data, alignment of traces and their stacking for amplifying studied phases, and grid search for the inversion. Joint interpretation of more phases converted/reflected from the same interface increases the stability of retrieved results and enhances the robustness of the inversion. A novel concept for extracting crustal structure from high-frequency waveforms of local microearthquakes is demonstrated on natural seismicity in the West Bohemia swarm region, the Czech Republic. Clustered seismicity in West Bohemia indicates a strong-contrast interface at depths of 3.5-6.0 km, which is in agreement with previous profiling and might be related to trapping of fluids ascending from the mantle.