Seismo Lab Seminar

Structure in the Earth is often investigated using seismic reflections. Especially for the mantle transition zone, precursors to PP and SS waves provide information of the depth of the discontinuity, which then allows to constrain the temperature and/or mineralogy of the region. Since the precursors are usually small, and often arrive near other waves, array seismology helps to detect the precursors. Generally, the arrival direction of the precursor is confirmed with array methods and only those waves that travel on the great circle path are retained. But out-of-plane waves have also been used to detect seismic structure in the mantle in areas where no source-receiver combinations are available. Using the slowness, backazimuth and travel time, we can back-project out-of-plane arrivals to subduction zones and to the LLSVP beneath the Pacific that are otherwise not accessible. ON the other hand, when ignoring the path deviations of waves that are usually assumed to be in plane, we find that even small slowness/backazimuth variations can generate travel time variations that, when back projected, reveal strongly different places and depth of the reflector. This could explain the variation in mantle reflector depths found in the literature. Our study shows the importance of knowing the travel path of waves for a better understanding of Earth structure.