Towards "Box Tomography" of Ultra-Low Velocity Zones at the Earth’s Core-Mantle Boundary
Description:
The earth’s core-mantle boundary (CMB) is a significant boundary for the exchange of energy and material between the liquid outer core and the silicate mantle. Ultralow-velocity zones (ULVZ) with extreme material properties have been detected at the base of Earth’s mantle through waveform modeling. The fine imaging of these small-scale objects requires seismic wave data with a period of 10 s or less and illumination from different directions. However, the computational time of global seismic simulations which increases as the 4th power of frequency makes the global waveform inversion of ULVZs challenging. Thus, “Box tomography” is being developed to improve image resolution of such kinds of target small-scale objects buried in the deep mantle. The computation of the wavefield consists of three parts: 1) from the sources to the boundary of the target region including the CMB, then inside the target region, and then from the boundary to the remote stations. The first and last parts are calculated using a global solver once and for all (here SPECFEM3D_globe), while the propagation inside the box is computed using a regional solver. At each iteration of the box tomography, the forward simulation is repeatedly performed only within the box, and the computational cost is proportional to the 3rd power of the size ratio between the box and the global Earth, making the higher resolution imaging possible (Adourian et al., 2022). In this study, after the implementation of the hybrid simulation, both for elastic and acoustic wave equations, and the absorbing boundary condition, we have designed a flexible way to combine two distinct solvers with different spatial meshes, including solid-fluid coupling across the CMB. Details of our approach and initial steps towards the imaging of the ULVZ at the root of the Iceland Plume are presented.
References
Adourian, S., Lyu, C.*, Masson, Y., Munch, F., and B. Romanowicz*. Combining different 3-D global and regional seismic wave propagation solvers towards box tomography in the deep Earth. GJI., 232(2):1340–1356, 10 2022. ISSN 0956-540X. doi: 10.1093/gji/ggac394.
Session: Numerical Modeling in Seismology: Developments and Applications
Type: Oral
Date: 4/20/2023
Presentation Time: 05:15 PM (local time)
Presenting Author: Chao Lyu
Student Presenter: No
Invited Presentation:
Authors
Chao Lyu Presenting Author lyuchao1988@gmail.com University of California, Berkeley |
Yder Masson yder_masson@berkeley.edu LMAP/LFCR/CNRS, Université de Pau et des Pays de l’Adour |
Liang Zhao zhaoliang@mail.iggcas.ac.cn Chinese Academy of Science |
Barbara Romanowicz Corresponding Author barbarar@berkeley.edu University of California, Berkeley |
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Towards "Box Tomography" of Ultra-Low Velocity Zones at the Earth’s Core-Mantle Boundary
Category
Numerical Modeling in Seismology: Developments and Applications