NS41B-1930
2D shear wave velocity mapping of the Hartoušov CO2 degassing area in the Cheb Basin, NW Bohemia (Czech Republic), using Multichannel Analysis of Surface Waves
Abstract:
For the characterization of the subsurface of the Hartoušov CO2 degassing area in the Cheb Basin, NW Bohemia, Czech Republic several different approaches have been made. However, no active seismic characterization has been presented, nor published. The Multichannel Analysis of Surface Waves (MASW) offers an useful tool to estimate vertical and horizontal velocity changes of the shallow subsurface. This can correlate to variations on rock elastic properties and/or fluid content, and represents the subsurface-layering.Surface waves were stimulated using a sledgehammer as source, and were measured with 48 vertical geophones with spacing of 1 m and the roll along method with a setup displacement of 2 m. Two source offsets, 10 m and 30 m, were used to increase the data quality and the resolution.
The analysis of propagation velocities leads to dispersion curves from which 1D shear wave velocity profiles can be inverted. Those will be interpolated to create a 2D ground stiffness map. The measurements were taken in the NW area of the main degassing zone and are partially in the same spot of former investigations, i.e. CO2 concentration and gas flux measurements, electric and gravimetric surveys and continuous seismic noise measurements.
Changes in the structure of the 2D velocity maps can be explained potentially with the occurrence of fluid paths and their diffusion in the subsurface or the existence of the Počatky-Plesná fault zone, which position is not fully understood yet or both features in combination.