UC Riverside

Earth’s interior has increasingly been shown to be highly heterogeneous and complex. By utilizing four seismic different methods, we seek to better constrain this heterogeneity at multiple depth and areal scales. We begin with Sp receiver function analysis across the Australian continent, which uses direct seismic phases and those converted at boundaries to estimate velocity contrasts at boundaries below a seismometer. Then, using Ps receiver function analysis we expand beyond this to not only examine these velocity contrasts but also test for changes in seismic anisotropy across said boundaries. Next, we examine shear wave splitting both in Australia and at a smaller scale in the Wyoming Craton: this method relies on the fact that when a shear wave encounters anisotropic material, it is split into two orthogonal components, which can be retrieved at the receiver side. Finally, we cross correlate components of a single seismometer to estimate shallow subsurface velocity changes following the Ridgecrest earthquake sequence. Results from the Australian Sp receiver function analysis show a sharp, shallow seismic lithosphere-asthenosphere boundary on the Phanerozoic east coast, with multiple mid-lithospheric discontinuities in the central cratonic portion. Our Ps receiver functions do not match well with simple models of seismic anisotropy changes across boundaries, but do exhibit characteristic backazimuthal variation: this implies more diffuse zones of seismic anisotropy. This is confirmed by our Australian shear wave splitting results, which show fast directions that often cannot be explained through plate-motion-induced shear alone and may require multiple layers of seismic anisotropy. Shear wave splitting in Wyoming also shows complexity in fast direction and delay time, but there appears to be a more systematic change in parameters moving into the Powder River Basin. Finally, velocity perturbations following the Mw 7.1 Ridgecrest sequence generally recover within hours to days, suggesting a largely elastic response. Two stations do not show a recovery within the time period examined, implying a plastic response instead. All results bolster an argument for interior complexity mirroring Earth’s surface.