[S16-1] Large low shear velocity provinces and deep mantle structure

[S16-1-03] Waveform inversion for localized three-dimensional shear wave velocity structure within the lowermost mantle

^○Kenji Kawai¹, Anselme Borgeaud¹, Yuki Suzuki¹, Kensuke Konishi², Robert Geller¹ (1.The University of Tokyo, Tokyo, Japan, 2.Institute of Earth Sciences, Academia Sinica, Taiwan)

We formulate the inverse problem of waveform inversion for localized 3-D seismic structure, computing partial derivatives of waveforms with respect to the elastic moduli at arbitrary points in space for anisotropic and anelastic media. In this study we minimize computational requirements by using the Born approximation with respect to a laterally homogeneous model, but this is not an inherent limitation of our approach. We solve the inverse problem using the conjugate gradient (CG) method, using Akaike's Information Criterion (AIC) to truncate the CG expansion. We apply our method to invert for 3-D shear wave structure in the lowermost mantle beneath Central America, the western and northern Pacific using waveforms at periods from 12.5 to 200 s recorded at stations of USArray and F-net for deep and intermediate-depth events. Various tests show that our model is robust.