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2021-2022

2021–2022 Webinar Schedule

October 14. SMOREs Showcase
January 13. Raj Moulik, Princeton UniversityIntroduction to reference Earth models and datasets using AVNI
February 17Takumi Kera, Tohoku UniversityEnergy transfer among flow and magnetic fields with different equatorial symmetry during the dipole reversal in a geodynamo simulation
March 10Ryan Orvedahl, UC DavisDynamo Simulations of Planetary Cores
April 14. Kali Allison, UC DavisInteraction Between Earthquakes and Interseismic Deformation
May 12. Robert Walker, University of BuffaloPoroelastic Implementation in PyLith: Gateway to Multiphysics


THURSDAY OCTOBER 14

Bayesian Uncertainty Quantification of Subduction Zone Rheology from the Geoid
Elena Ehrlich, North Carolina State University

Early Earth Influence of Radiogenic Heating on Mid-Ocean Ridge Depths and Seafloor Subsidence
Keneni Godana, University of Illinois at Chicago

As Above So Below: A Simulation of the Continental Lithosphere and LLSVPS as Thermal Insulators using ASPECT
Dante Hickey, Reed College

Interactions between Lithospheric Instabilities and Formation of Mantle Plumes in Venus
Hiva Mohammadzadeh, Los Angeles Pierce College

Members of the geodynamics community come from a broad range of fields. Many of these fields are among the least diverse in STEM. The challenges for computational geodynamics are not only to increase competency in earth and computational science but also in recruiting from an undergraduate student pool that in itself lacks diversity. The CIG 2021 Summer MOdeling Research Experiences (SMOREs) pilot program focused on addressing these issues by providing underrepresented groups funded training and research opportunities. In total, 4 applicants from a broad range of backgrounds and expertise were selected for the program out of 35 highly qualified applications. Following 2 weeks of virtual tutorials, the applicants worked with mentor pairs at different CIG-member institutions on projects ranging from mantle dynamics to magmatism within the lithosphere. This webinar will contain a short, AGU-style presentation from each SMOREs participants on the results of their summer research and plans going forward. We welcome all members of the community to join for the conclusion of the pilot CIG program! [intro] [Ehrlich] [Godana][Hickey][Mohammadzadeh]

THURSDAY JANUARY 13

Introduction to reference Earth models and datasets using AVNI
Pritwiraj ‘Raj’ Moulik, Princeton University

• Open-source Python package with APIs to handle data and compute intensive queries

• Introduce storage formats or classes for models and processed seismic data 

• Interactive web-based visualization tools for data and model exploration 

• Formulate and benchmark forward solvers for rapid data validation of models 

Modeling the interior structure of terrestrial planets has become one of the most computationally-intensive, big-data problems in the physical sciences with demonstrated utility in assessing hazard, locating explosions and characterizing plate tectonics. Multi-disciplinary advancements have led to a proliferation of dynamical simulations and model snapshots from seismic tomography. Reconciling seismic models and data with simulations from geodynamics, mineral physics and geochemistry is crucial for robust thermo-chemical interpretations. Such cross-disciplinary initiatives have been impeded by discrepant spatial scales, observational or theoretical assumptions, and lack of data validation algorithms. AVNI is an Analysis and Visualization toolkit for plaNetary Inferences that will handle model and data queries from the 3D reference Earth model (REM3D) project.

We present methods and data formats that facilitate rapid prototyping of multi-scale models by reconciling and assimilating features ranging from reservoir (~0.1 - 10 km) to global scales (~500 - 5000 km). Our approach involves three complementary aspects: (1) Code repositories comprising modular libraries with model classes and scalable HDF5 formats for archival, (2) API (Application Programming Interface) calls for querying model and data evaluations with fast, benchmarked forward solvers, (3) Web-based applets for visualization and outlier analyses. Both (1) and (2) are utilized by (3) and can be accessed on the client side with Jupyter notebooks and command-line tools.

AVNI aids reconciliation of measurements made using different techniques by identifying (in)consistent features and subsequently models them using a flexible scheme that permits almost instantaneous forward calculations of data. The methodology employs in-memory and filesystem data storage, providing rapid and scalable filtering of Earth models and calculation of seismic observations. By coupling existing, reconciled observations with predictions for arbitrary locations, this application will be a useful tool for identifying regions of scientific interest, validating new techniques, planning future seismic deployments, and testing hypotheses about the Earth's deep interior.

THURSDAY FEBRUARY 17

Energy transfer among flow and magnetic fields with different equatorial symmetry during the dipole reversal in a geodynamo simulation
Takumi Kera, Tohoku University

[movie]

The geomagnetic field has reversed its polarity, and some numerical dynamos have suggested that anti-symmetric flow with respect to the equator plays a role in reversals. Olson et al., (2004) suggested that the equatorial antisymmetric flow is temporarily strengthened, and transports a locally generated reversal magnetic field. Nishikawa and Kusano (2008) explained this asymmetric velocity field enhancement by the increase of energy transfer from magnetic field to asymmetric velocity field in polarity reversal phase by the Lorentz force by simulation with the large magnetic Prandtl number (Pm = 15). In the present research, we investigate how anti-symmetric flow merges and is sustained in the dynamo in which reversals occur with Pm = 5 and Ekman number E = 6e-3.

We perform dynamo simulations using Calypso (Matsui et al., 2014) to represent dipole dominant dynamo with reversals. We investigate the buoyancy flux and work of the Lorentz force in terms of the equatorial symmetry in the stable polarity phase and in the polarity reversal phase, respectively.

The results show that strong upwelling plumes emerge during the reversal (see Movie). This temperature field suggests that this plumes cause the high amplitude of asymmetric buoyancy flux. However, looking at the kinetic energy spectra, the amplitude of the axisymmetric and antisymmetric poloidal flow has small changes, while a characteristic increase in the toroidal component of the axisymmetric and antisymmetric flow is observed. This result suggests that the toroidal component may play a more important role in reversals. Consequentially, more investigation is required if meridional circulation has an important role for a dipole reversal.

Looking at the energy transfers for the flows during the reversal, the buoyancy flux and work of the advection term to the antisymmetric velocity field increase from the time average in the stable phase. On the other hand, the work of the Lorentz force for the antisymmetric flow has smaller change from the time average than that for the buoyancy flux and work of the advection term. [pdf]

THURSDAY MARCH 10

Dynamo Simulations of Planetary Cores
Ryan Orvedahl, UC Davis

The majority of solar system planets possess global, or large-scale, magnetic fields. These magnetic fields are all thought to be generated by the dynamo mechanism, whereby kinetic energy associated with a convectively stirred plasma is converted into electromagnetic energy. Most planets have a large-scale magnetic field that is aligned with its rotation axis and often are characterized by a relatively strong dipolar component. In this work, large-scale magnetic field properties are investigated using rapidly rotating numerical simulations in a sphere. The large-scale magnetic field saturates as the intensity of convective motions is increased. The saturation is explored over a wide range of system parameters and is found to be a robust feature of rapidly rotating dynamo simulations. These results are described using a semi-magnetostrophic force balance, where the Lorentz force enters the leading-order mean force balance in only a single component direction. These simulations are generated using the Rayleigh pseudo-spectral code and current software development plans for its improvement will also be discussed.

THURSDAY APRIL 14

Interaction Between Earthquakes and Interseismic Deformation
Kali Allison, UC Davis

Earthquake cycle models can be used to understand the processes that govern fault and shear zone structure and to link these processes to earthquake cycle characteristics, such as earthquake size and recurrence interval. These models connect such disparate data types as: laboratory data on rock deformation mechanisms, geodetic measurements of surface deformation, and microstructural observations of exhumed faults. In this talk, I review the current state of earthquake cycle modeling, placing it in the context of other approaches to modeling earthquakes. Then, using the simplest earthquake cycle model which includes both spontaneous earthquakes and viscoelastic deformation, I explore the interaction between coseismic and aseismic fault slip and viscoelastic deformation. Finally, I will discuss the effects of incorporating two mechanisms, shear heating and grain size reduction, both of which weaken the root of the fault and alter the structure of the shear zone. 

THURSDAY MAY 12

Poroelastic Implementation in PyLith: Gateway to Multiphysics
Robert Walker, SUNY Buffalo

PyLith, a community, open-source code (https://geodynamics.org/resources/pylith) for modeling quasi-static and dynamic crustal deformation with an emphasis on earthquake faulting, has recently been updated with a flexible multiphysics implementation. We demonstrate the versatility of the multiphysics implementation by extending the code to model fully coupled continuum poromechanics.

We verify the newly incorporated physics using standard benchmarks for a porous medium saturated with a slightly compressible fluid. The benchmarks include Terzaghi’s consolidation problem for the one-dimensional case, Mandel’s problem for the two-dimensional case, and Cryer’s problem for the three-dimensional case; all three benchmarks have been added to the PyLith continuous integration test suite. We compare the closed form analytical solution for each benchmark against solutions generated by our updated code.