Can We Explain the D" Reflector with the Post-Perovskite Phase Transition?

Abstract:

Seismic observations from the lower Earth's mantle indicate a reflector that marks the top of the D" region. Many studies have imaged this reflector in previous years, many of them in high-velocity regions that could be due to slab graveyards, and many interpretations have been published previously. Since the discovery of the post-perovskite phase transition ten years ago, the D" reflector has often been interpreted as the place of the phase transition. Even looking at waveforms, polarities, deeper reflectors and amplitudes of the reflected waves has shown agreement with properties of post-perovskite and the confidence of it as the cause for the D" reflector has been increasing. Here we are looking at several new places and identify D" reflections in P and S-waves: we target especially low velocity regions and places, where we do not expect slab material in the lowermost mantle. We test waveforms, polarities, amplitudes, timing and frequency content of the reflected waves and compare these across many diverse regions in the mantle. It seems that post-perovskite can still explain many observations; however, a large number of assumptions has to be made to explain all observations in all regions simultaneously and leaves the question whether the reflector in D" can always be explained through a phase transition to post-perovskite or whether we have to consider other possibilities.