Dan J. Bower

Dynamic origins of small-scale lateral wavespeed variation in the deep Earth with application to Central America mantle structure.

Collaborating with Michael Gurnis^a, Daoyuan Sun^ab, and Don V. Helmberger^a.

^aSeismological Laboratory, Caltech, Pasadena, CA, USA; ^bCarnegie Institution, Washington, DC, USA.

We explore the origins of D'' seismic waveform complexity using a velocity model derived from a 2-D compressible thermal convection model with the post-perovskite phase transition and self-consistent generation of slabs. Our study provides insight into the dynamic processes that may be responsible for D'' seismic complexity as identified through the analyses of dense broadband array data. The convection model includes depth-dependent material parameters and viscous, adiabatic, and latent heating. We utilize a viscoplastic rheology to model tectonic plate-like behavior and enable slabs to propagate to the core-mantle boundary region. Cold slab material strongly deflects the post-perovskite phase boundary and modulates plume formation. The temperature and phase field from the geodynamic simulation are mapped to seismic velocity perturbation using a mineral physics formulation, and we generate synthetic seismograms using a 2-D wave propagation code. The lateral juxtaposition of strong thermal and phase gradients from the simulation are manifest in waveform complexity observed in the synthetic seismic data, such as the generation of Scd phases. Thermochemical modeling and the inclusion of P-wave data may provide constraints on compositional effects.

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