Imaging global body wave phases by stacking long‐period seismograms

Stacked record sections combining over 5 years of long‐period Global Digital Seismograph Network (GDSN) seismograms from shallow events show dozens of seismic body wave phases. Separate images are obtained for the vertical, radial, and transverse components using an automatic gain control algorithm which normalizes the amplitude of each trace prior to stacking. These images provide an indication of the relative signal‐to‐noise characteristics of different parts of the GDSN data set. Core‐mantle boundary diffracted phases are particularly prominent in these stacks, which show P diff to 150°, PKP diff to 200°, PP diff to 230°, S diff to 160°, and SS diff to 220°. High‐order S surface multiples can be seen extending through the surface wave train up to ranges of 540°. Two examples of possible upper mantle discontinuity reflected phases are visible, one following PPP between about 95° and 125°, the other following ScS 3 between about 210° and 240°. An apparent offset between SH and SV arrivals is seen which becomes larger for the higher‐order S multiples ( SSS, SSSS , etc.), and appears consistent with models containing transverse isotropy in the upper mantle.