Soft Soil Amplification of Ambient Seismic Noise – Field Measurements and Numerical Modeling of H/V Ratios

Modifications of the seismic background noise spectrum were observed above hydrocarbon reservoirs (‘hydrocarbon tremors’). Other effects, such as for example the presence of soft soil layers, can also amplify the background noise at certain frequencies. The effect of soft soil amplification is widely used to derive resonance frequencies of the site as well as the S-wave velocity and thickness of the soil layer. One of the most popular techniques to determine those values is the so called Nakamura’s H/V spectral ratio technique. We observe soil related modifications in our measured data and we are able to reproduce those effects with a 2D finite difference wave propagation model. The synthetic results match very well the analytical predictions. Such simulations help to clean measured data from soft soil related effects and thus to improve the identification of hydrocarbon related information in the microtremor spectra.