Figure 6. The source spectrum obtained from the LVIG recording alone (continuous curve), and the median and ±one standard deviation source spectra (dashed curves) for the events of group B. Dotted curves show source spectra retrieved from station PNIG. Note that a PNIG recording is not available for all events. Q(f) = 273f^0.66 for the interplate B5 event; for all others events Q(f)=251f^0.58.