For each array, we also construct vespagrams, assessing the incoming signal coherence (via the F-statistic) as a function of time and ray parameter, to confirm that the signals being received are originating from the correct geographic region ( Fig. 5). Spatial CCT244747 for the signal source is relatively poor, due to the small aperture width of the arrays used, particularly for the smaller arrays at MKAR, PETK and USRK (apertures of ∼4 km). However, similarities between the apparent slowness of the direct arrival and of later arriving signals serves to confirm that the interpreted signal is not background noise, and is not a coherent signal from another spatially-separated source.
A clear pP arrival can be seen in both the beam and the F-trace at ESDC, and this is then followed by a low amplitude, high coherence signal consistent with sP. The sP phase is particularly clear in both the beam and F-trace at ILAR and USRK. MKAR and PETK also show evidence for low-amplitude, high-coherence arrivals, although in both cases blending are slightly later than predicted. All arrays show the arrival of low amplitude signals, low coherence arrivals at other points in the waveform, both before and after the much larger amplitude depth phase arrivals. Whilst the vespagrams demonstrate that these are indeed coherent signals originating from the approximate source region, given their similar apparent slownesses to the direct arrival, due to their low amplitude, we interpret these as Moho/intracrustal reflections and conversions, arising from impedance contrasts in either the near-source or near receiver velocity structure.
A clear pP arrival can be seen in both the beam and the F-trace at ESDC, and this is then followed by a low amplitude, high coherence signal consistent with sP. The sP phase is particularly clear in both the beam and F-trace at ILAR and USRK. MKAR and PETK also show evidence for low-amplitude, high-coherence arrivals, although in both cases blending are slightly later than predicted. All arrays show the arrival of low amplitude signals, low coherence arrivals at other points in the waveform, both before and after the much larger amplitude depth phase arrivals. Whilst the vespagrams demonstrate that these are indeed coherent signals originating from the approximate source region, given their similar apparent slownesses to the direct arrival, due to their low amplitude, we interpret these as Moho/intracrustal reflections and conversions, arising from impedance contrasts in either the near-source or near receiver velocity structure.