P- andS-wave reflectors in D″ beneath southeast Asia

Abstract

Earthquakes from the South Pacific region recorded at the Kyrgyz Seismic Network (KNET) and the GHENGIS network (both part of the Tien Shan Continental Dynamics study) have been analysed to search for evidence of reflections from the D″ region. The reflection points of this source—receiver combination are in a seismically fast area beneath Southeast Asia. Employing several array methods, we find evidence for reflections from a D″ reflector in both P and S waves. The reflector depth generally agrees for both wave types. There is some evidence for a second, deeper reflector in this region; migrating the data suggests a lower-seismic reflector beneath the northeastern end of the study region. The waveforms of P and S waves imply that the upper reflector has a negative impedance contrast for P but a positive impedance contrast for S. Several possibilities are discussed for generating the observed reflector(s), with the post-perovskite phase transition in combination with a cold slab being the preferred explanation.