Comparing single-station 6C measurements and array measurements for seismic microzonation in Munich, Germany

Abstract

SUMMARY The essential goal of seismic microzonation is the estimation of the shallow velocity structure in order to characterize the local earthquake shaking characteristics. This is of special importance in densely inhabited areas with unfavourable soil conditions. The common approach is the analysis of ambient noise array data using frequency–wavenumber (FK) or spatial autocorrelation (SPAC) techniques. However, the installation of arrays is difficult, especially within urban environments, making single-station approaches more desirable. In this study, we directly compare the recently developed approach of velocity estimation using single-station six-component (6C) measurements, combining three translational and three rotational motions, with the established methods of FK and SPAC analysis. We conduct measurements in Munich’s inner city using a geophone array and an iXblue blueSeis-3A rotational motion sensor together with a Nanometrics Trillium Compact Seismometer, respectively. From the array data, as well as from the 6C data, Love and Rayleigh dispersion curves are estimated and further inverted for 1-D P- and S-wave velocity profiles. We find that all methods give similar results, indicating the potential of the novel 6C approach. Furthermore, adding horizontal-to-vertical spectral ratios enables the inversion for structures at greater depth and increases the resolution of the velocity structure. In addition, we test different array geometries to evaluate the influence of the sensor configuration on the results. As a last step, we compare the estimated velocity models to lithologic profiles and find an overall positive correlation, which supports our inversion results.