S018-0004
Radial anisotropy of the Alaskan lithosphere revealed by multi-component ambient-noise adjoint tomography

Wednesday, 9 December 2020
Poster
Tianshi Liu1, Kai Wang2, Carl Tape3, Bin He4, Yingjie Yang2, Ping Tong5 and Qinya Liu4, (1)University of Toronto, Department of Earth Sciences, Toronto, ON, Canada, (2)Macquarie University, ARC Centre of Excellence for Core to Crust Fluid Systems and GEMOC, Sydney, NSW, Australia, (3)University of Alaska Fairbanks, Geophysical Institute, Fairbanks, AK, United States, (4)University of Toronto, Department of Physics, Toronto, ON, Canada, (5)Nanyang Technological University, Singapore, Singapore
Abstract:
Multiple episodes of tectonic events have shaped the unique and complex geological structures in Alaska. Seismic imaging allows us to map the subsurface structures, providing constraints on the tectonic evolution of the region. In particular, seismic radial anisotropy is considered to be related to both lithology and deformation history of the lithosphere, and therefore plays an important role in understanding past tectonic processes.

In this study, we use high-quality broadband seismic records over the entire Alaska from the recent deployment of USArray (IRIS DMC 2010) to image the radial anisotropy of the crust and uppermost mantle beneath Alaska. We collect all available continuous seismic data recorded from 2014 to 2019 at the broadband stations in Alaska, and follow the standard ambient noise data processing procedures of Bensen et al. (2007) to extract the vertical-vertical (Z-Z), radial-radial (R-R) and transverse-transverse (T-T) components of the empirical Green’s functions (EGF) between all available station pairs. Based on the adjoint method of Tape et al. (2007), we measure and minimize the frequency-dependent travel-time misfits between EGFs and simulated Green’s functions of all the three components at 12-50s to update the velocity model iteratively on top of an isotropic initial 3D model recently obtained by ambient-noise adjoint tomography.

We follow Wang et al. (2019) to carry out forward and adjoint simulations for the three components efficiently. We also apply the mini-batch technique (e.g., van Herwaarden et al. 2020) in order to further accelerate the inversion. The use of all three components of EGFs enables us to map both vertically (Vsv) and horizontally (Vsh) polarized S-velocities from the surface down to ~70km depth, based on which we construct a radial anisotropy model of the Alaskan lithosphere. Our radial anisotropy model along with the isotropic Vs model helps to better understand the deformation history of the lithosphere beneath Alaska.

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