Fig. 6
a P-wave and S-wave velocities of the sedimentary cover around Saint-Ursanne estimated from NAGRA borehole logs in NE Switzerland. The average velocity is 4.2 km/s. b Diagram of Pg, Pn, PmP, and sPmP rays travelling through the crust from the hypocenter (star) to the station (triangle). c Recording stations during the 2000 sequence. Dashed line indicates the profile used in the calculation for the synthetic modelling. Stations shown in Fig. 7 are circled in magenta, whereas green circles indicate the stations shown in d). d) Reduced travel times (Vred = 6.0 km/s) as a function of epicentral distance (D) along the profile in the NE direction shown in (c) for real data from the main shock of the Saint-Ursanne sequence (ML 3.2 event of 2000/04/06 00:46:6.0). Arrivals along the green horizontal line have an apparent velocity of 6.0 km/s and have travelled through the upper crust (Pg). The arrivals along oblique lines beyond about 120 km are Pn arrivals, indicating arrivals refracted at the Moho. Note the relatively emergent Pg-onsets at the first three stations compared to the relatively strong and impulsive Pn-onsets beyond 140 km