I am actively seeking new graduate students, seeking either Masters or PhD degrees, for my research group. After spending my sabbatical enabling subduction modeling using the simulation code called Aspect, I have several research projects for graduate students to work on. Due to the nature of the research topics and tools used in our research potential graduate students should have a strong mathematics (including linear algebra and differential equations) and geophysics (or physics, fluid dynamics or continuum mechanics) background, with some experience in computer programming (e.g., matlab, python,…), and a strong interest in building on these skills extensively. Students with a Batchelors (BS) or Masters (MS) degree in engineering or physics looking to shift to geophysics for graduate school, as well students with a BS /MS degree in geophysics or geology with an emphasis in geophysics, are strongly encouraged to contact Dr. Billen for more information about potential research projects and how to apply.

# Author Archives: billen

# Fate of Slabs and Stirring – Magali’s Lecture at CIDER, 2018

The fate of slabs as they sink into the upper most lower mantle is a important question for understanding the history of our planet. Do slabs actually make it to the core-mantle-boundary? How can we interpret the fast seismic anomalies that we see in seismic tomography images?Can we make geologic-type reconstructions of slabs linking seismic tomography images to models of plate motions in time? This CIDER 2018 lecture provides an overview of observations, the basic physical principles that govern the dynamics of slabs as they sink through the upper mantle and into the lower mantle, and presents example cases that illustrate how slabs interact with changing viscosity structure and upwellings in the lower mantle. A major take-away from the examples is that the present-day geometry of a slab does not necessarily tell you the path the slab took to reach that point (a basic principle from structure geology… there are multiple strain path to reach a final state of deformation). A PDF of the talk can be found on the CIDER wiki page as well as a video of the actual lecture.

# Decoupling Plate-Asthenosphere Motion with Non-linear Rheology

In a new paper to appear in* Physics of the Earth and Planetary Interiors* , Magali Billen and Katrina Arredondo (PhD 2016) show that during episodes of slab folding in the transition zone the overriding plate and the underlying asthenosphere can flow in opposite directions. This occurs as rapid sinking of the slab in the transition zone causes the viscosity to drop to less than 10^19 Pa-s around the slab and beneath the overriding plate. Such low viscosity allows the asthenosphere to be pulled toward the slab, while the overriding plate is pushed by the advancing motion of the subducting plate and shallow slab.

# Jupyter Notebooks for Geodynamics

One of the projects for my sabbatical is to learn Python. Luckily its easier than I had thought it would be, at least so far. I have started making some jupyter notebooks with useful geodynamics-related calculations, especially related to subduction. For example, the sinking velocity for a Stokes ellipsoid (rather than a sphere), corner flow and plate bending forces. I am posting these jupyter notebooks on my web-page so others can download them and use them in their research or teaching. For me, I’ve found that the notebooks are a great way combine my thinking, derivation of equations, the actual calculation and figures.

# Biology meets Subduction

Subduction is not just about mountain building, volcanoes and driving the plate tectonics systems, its also about biology. Check out this video following an expedition of young geo-biologist, geo-chemist, and geologists exploring how and where biology thrives in the Costa Rica Subduction Zone.

# Research Presentation at Universität Münster, Geophysik

Dr. Billen will be giving a research presentation, “Spontaneous Arc Rifting” on Monday, November 13th at 4 pm in the Geophysics Department at the University of Muenster. The talk will present background on how rifting of arcs evolves to form back arc spreading centers, previous models for how this occurs, numerical models of subduction with a new mode of arc rifting and the implications for thermal structure and melting during rifting, and changes in plate motions. This talk is based on a paper that is in press at Geophysical Research Letters.

# Subduction Modeling Videos

I’ve added a new page to the website making videos of many of our published subduction models available for use in teaching or research talks. Check it out!

# Presentations at GSA 2017

Strangely, I have never been to GSA before, but this year I am making up for this and presenting 3 talks and 1 poster at GSA.

Talks:

A SYNTHESIS OF RECENT RESULTS FROM GEODYNAMIC MODELS OF SUBDUCTION INITIATION AND TERMINATION

THE EFFECT OF SPREADING RIDGES AND BUOYANT CRUST ON THE DYNAMICS OF SUBDUCTION

Poster

EVOLUTION OF SLAB AND WEDGE THERMAL STRUCTURE IN TIME-DEPENDENT DYNAMIC MODELS OF SUBDUCTION

# New Mode of Arc/Forearc Rifting

Numerical models of subduction show that spontaneous rifting of the arc or forearc may occur due to an in situ instability in the mantle wedge corner. This new mode of arc/forearc rifting is explained in a journal article by Dr. Billen, that is now in press at *Geophysical Research Letters.*

# Sabbatical in Munich 2017-2018

I am on sabbatical at Ludwig Maximiliian University in Munich, Germany for the 2017-2018 academic year. I’m being hosted by Prof. Heiner Igel, head of the seismology group.