Planet-scale MRI
High resolution illumination of Earth's interior down to the planet's
core with 3D global numerical simulations

Date:
March 29, 2022
Source:
University of Texas at Austin, Texas Advanced Computing Center
Summary:
Researchers presented the results of efforts to perform
global full waveform inversions of the Earth using the Frontera
supercomputer. They used data from 300 earthquakes to construct the
new global full wave inversion models that include attenuation and
azimuthal anisotropy and approach continental-scale resolution. The
researchers also recently released a visualization toolbox for
large seismic model files and are building a platform for seismic
analysis.



FULL STORY ========================================================================== Earthquakes do more than buckle streets and topple buildings. Seismic
waves generated by earthquakes pass through the Earth, acting like a
giant MRI machine and providing clues to what lies inside the planet.


========================================================================== Seismologists have developed methods to take wave signals from the
networks of seismometers at the Earth's surface and reverse engineer
features and characteristics of the medium they pass through, a process
known as seismic tomography.

For decades, seismic tomography was based on ray theory, and seismic waves
were treated like light rays. This served as a pretty good approximation
and led to major discoveries about the Earth's interior. But to improve
the resolution of current seismic tomographic models, seismologists
need to take into account the full complexity of wave propagation using numerical simulations, known as full- waveform inversion, says Ebru
Bozdag, assistant professor in the Geophysics Department at the Colorado
School of Mines.

"We are at a stage where we need to avoid approximations and corrections
in our imaging techniques to construct these models of the Earth's
interior," she said.

Bozdag was the lead author of the first full-waveform inversion model,
GLAD-M15 in 2016, based on full 3D wave simulations and 3D data
sensitivities at the global scale. The model used the open-source
3D global wave propagation solver SPECFEM3D_GLOBE (freely available
from Computational Infrastructure for Geodynamics) and was created in collaboration with researchers from Princeton University, University of Marseille, King Abdullah University of Science and Technology (KAUST)
and Oak Ridge National Laboratory (ORNL). The work was lauded in the
press. Its successor, GLAD-M25 (Lei et al. 2020), came out in 2020
and brought prominent features like subduction zones, mantle plumes,
and hotspots into view for further discussions on mantle dynamics.

"We showed the feasibility of using full 3D wave simulations and data sensitivities to seismic parameters at the global scale in our 2016 and
2020 papers. Now, it's time to use better parameterization to describe
the physics of the Earth's interior in the inverse problem," she said.



==========================================================================
At the American Geophysical Union Fall meeting in December 2021,
Bozdag, post- doctoral researcher Ridvan O"rsvuran, PhD student Armando Espindola-Carmona and computational seismologist Daniel Peter from KAUST,
and collaborators presented the results of their efforts to perform
global full waveform inversion to model attenuation -- a measure of
the loss of energy as seismic waves propagate within the Earth -- and
azimuthal anisotropy -- including the way wave speeds vary as a function
of propagation direction azimuthally in addition to radial anisotropy
taken into account in the first-generation GLAD models.

They uses data from 300 earthquakes to construct the new global full
wave inversion models. "We update these Earth models such that the
difference from observation and simulated data is minimized iteratively,"
she said. "And we seek to understand how our model parameters, elastic
and anelastic, trade-off with each other, which is a challenging task."
The research is supported by a National Science Foundation (NSF) CAREER
award, and enabled by the Frontera supercomputer at the Texas Advanced Computing Center -- the fastest as any university and the 13th fastest
overall in the world -- as well as the Marconi100 system at Cineca,
the largest Italian computing center.

"With access to Frontera, publicly available data from all around the
world, and the power of our modeling tools, we've started approaching the continental- scale resolution in our global full wave inversion models,"
she said.

Bozdag hopes to provide better constraints on the origin of mantle
plumes and the water content of the upper mantle. Furthermore, "to
accurately locate earthquakes and other seismic sources, determine
earthquake mechanisms and correlate them to plate tectonics better,
you need to have high-resolution crustal and mantle models," she said.



==========================================================================
From the Deepest Oceans to Outer Space Bozdag's work isn't only relevant
on Earth. She also shares her expertise in numerical simulations with
the NASA's InSight mission as part of the science team to model the
interior of Mars.

Preliminary details of the Martian crust, constrained by seismic data
for the first time, were published in Science in September 2021. Bozdag, together with the InSight team, is continuing to analyze the marsquake
data and resolve details of the planet's interior from the crust to the
core with the help of 3D wave simulations performed on Frontera.

The Mars work put in perspective the dearth of data in some parts of the
Earth, specifically beneath oceans. "We now have data from other planets,
but it is still challenging to have high-resolution images beneath the
oceans due to lack of instruments," Bozdag said.

To address that, she is working on integrating data from emerging
instruments into her models as part of her NSF CAREER award, such as
those from floating acoustic robots known as MERMAIDs (Mobile Earthquake Recording in Marine Areas by Independent Divers). These autonomous
submarines can capture seismic activity within the ocean and rise to
the surface to deliver that data to scientists.

Seismic Community Access In September 2021, Bozdag was part of a team
awarded a $3.2 million NSF award to create a computational platform for
the seismology community, known as SCOPED (Seismic COmputational Platform
for Empowering Discovery), in collaboration with Carl Tape (University
of Alaska-Fairbanks), Marine Denolle (University of Washington), Felix Waldhauser (Columbia University), and Ian Wang (TACC).

"The SCOPED project will establish a computing platform, supported
by Frontera, that delivers data, computation, and services to the
seismological community to promote education, innovation, and discovery,"
said Wang, TACC research associate and co-principal investigator on the project. "TACC will be focusing on developing the core cyberinfrastructure
that serves both compute- and data- intensive research, including seismic imaging, waveform modeling, ambient noise seismology, and precision
seismic monitoring." Another community-oriented project from Bozdag's
group is PhD student Caio Ciardelli's recently released SphGLLTools:
a visualization toolbox for large seismic model files. The toolbox
based facilitates easy plotting and sharing of global adjoint tomography
models with the community. The team described the toolbox in Computers & Geosciences in February 2022.

"We provide a full set of computational tools to visualize our global
adjoint models," Bozdag said. "Someone can take our models based on
HPC simulations and convert them into a format to make it possible to
visualize them on personal computers and use collaborative notebooks
to understand each step." Said Robin Reichlin, Director of the
Geophysics Program at NSF: "With new, improved full-waveform models;
tools to lower the bar for community data access and analysis; and a supercomputing-powered platform to enable seismologists to discover
the mysteries of the Earth's and other planetary deep interior, Bozdag
is pushing the field into more precise, and open, territory." Video: https://youtu.be/ilna9RAX6r8

========================================================================== Story Source: Materials provided by University_of_Texas_at_Austin,_Texas_Advanced_Computing Center. Original written by Aaron Dubrow. Note: Content may be edited for style and length.


========================================================================== Journal Reference:
1. Caio Ciardelli, Ebru Bozdağ, Daniel Peter, Suzan van der Lee.

SphGLLTools: A toolbox for visualization of large seismic model
files based on 3D spectral-element meshes. Computers & Geosciences,
2022; 159: 105007 DOI: 10.1016/j.cageo.2021.105007 ==========================================================================

Link to news story: https://www.sciencedaily.com/releases/2022/03/220329142533.htm

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