Relative travel time residuals for teleseismic events at the new Swiss seismic station network

Relative travel-time residuals of 133 earthquakes and 20 nuclear explosions recorded by the new Swiss seismic station network in the distance range from 30 to 100 degrees were analysed. The theoretical travel times were calculated by using the Herrin P-tables. These travel times were corrected for the elevation of the stations and the geologic structure down to the crystalline basement. An expected time delay between the Alpine stations and the ones in the northern Alpine foreland caused by the thicker Alpine crust could not be detected. An azimuthal variation of the residuals was found although not well pronounced for all the stations. This results supports a model of the upper mantle with higher average velocities beneath the crest of the Alps than underneath the northern Alpine foreland. In the area of investigation lateral inhomogeneities in the upper mantle seem to extend to depths of at least 220 km