Mapping sediment depths using seismic arrays, rotational measurements, and spectral ratios

Abstract

Unconsolidated sediments can amplify ground motions, increasing seismic hazard. Horizontal-to-vertical spectral ratios can derive the thickness of sediments overlaying stiffer bedrock. However, additional information about shear velocities and calibration with other structural information is necessary. Here, we propose a strictly ambient seismic noise-based workflow that can map the depth of sediments without additional information from other data sources. Rayleigh wave dispersion curves and ellipticities are derived from three-component beamforming of ambient noise and combined with dispersion curves from six-component measurements and horizontal-to-vertical spectral ratios. This is used to calibrate empirical relations between frequencies of extreme points in spectral ratio curves with depths of sediments. Applying the relations to more than forty seismic station data, we can map the depth of the Tertiary sediments at the southern margin of the lower Rhine embayment, Germany.