Figure 3 is a global travel-time plot made using 582,494 picks from 37,710 short-period seismograms from 3,046 events. Note the large number of picks per seismogram, a result of the low trigger threshold used for this plot (the majority of these picks can be thought of as ``noise'' since they do not line up in coherent phases). We only show the results for the vertical component since there are insufficient horizontal short-period data to produce meaningful images. A comparison of this plot with the data density (Figure 2a) shows that the ``graininess'' in the image is greatest where there is little data, whereas in densely sampled areas (e.g. near the P-wave) the image becomes smoother and the ``background'' rate of random picks becomes more uniform.
At ranges past about 100
P is diffracted around the core and is
termed Pdiff. In our picks Pdiff can be seen to a distance of 115 .
Poor data coverage makes it unclear if Pdiff extends beyond this. PKP(AB) and
PKP(BC) can be seen out to 175 at which point they are obscured due to a
lack of data. PcP is imaged from 25 to 62 . PP can be seen from
32 to 170 . PKPPKP (P'P') is visible in the range of its bright
BC branch (50 to 70). The S arrival (15 to 85) is not
well imaged in these vertical-component data. PKKP appears between 90 and
125. A bright spot in SKP can be seen following PP at a range of
130. ScP and SKKP are barely visible at ranges 30 to
80 and 100 to 130 respectively.
