Congratulations to Samuel Haugland who defended his dissertation on March 15, 2019

Advisor: Jeroen Ritsema

Plate tectonics is the surface expression of mantle convection and is driven by subducting oceaniclithosphere. Despite decades of research, the fate of subducted material remains uncertain. Methods of global seismology provide the means to determine how subducted material is distributed and to measure its elastic properties. I will discuss two seismic observations and what they can tell us about the nature, scale, and distribution of subducted material in the mantle. In the first study, broadband US Array recordings of an earthquake beneath Western Brazil reveal a fragment of oceanic crust entrained at 1750 km depth. With spectral element waveform modeling I measure its elasticity and compare to mineral physics estimates of eclogite elasticity at deep mantle conditions. In the second study, I show how high-frequency global stacks of scattered energy from the core-mantle boundary are consistent with structures calculated with geodynamic mantle convection models.