Waveform Complexity in Teleseismic Broadband Sh Displacements: Slab Diffractions or Deep Mantle Reflections?

Transverse component bodywave ground displacements from deep focus earthquakes exhibit complexities which are not accounted for by standard radially symmetric Earth models. This anomalous behavior is examined using 123 broadband teleseismic SH displacement recordings, reconstituted from shortand long-period or broadband seismograms for 11 events in the Kurile subduction zone. The greatest complexity, involving an extra arrival between the S and ScS phases at epicentral distances greater than 72 ø, has a strong distance dependence and little azimuthal variation with respect to the source region, favoring an interpretation as a deep mantle triplication rather than a near-source slab diffraction.