Fig. 5

Site-to-reference spectral ratio as a function of distance for ambient vibration Survey B (for location, see Fig. 1). The black line reflects the average over the frequency band, which comprises the values 4–4.5 Hz. Seismic sensors are marked as black squares. Station 1 is situated at zero distance, and has Swiss coordinates 634,921.2/125,679.7. Shown are: a fault-normal; b fault-parallel component (i.e. horizontal, perpendicular to fault-normal); c vertical component. Clearly visible is an amplitude reduction from station 1 to station 8 (normal and parallel component) and from station 1 to station 7 (vertical component). The zone with reduced spectral ratio potentially localizes a low velocity zone and can be measured along a distance of about 33 m