Dr. Rachel Bernard presented an excellent on how CPO type in olivine does (or actually doesn’t) depend on the tectonic setting or water content at low stresses – in stark contrast to experimental data the predict CPO type to cluster based on applied stress and water content.
Dr. Bernard also presented her analysis of ethnic and racial diversity published in Nature Geosciences – there is been no improvement in 40 years.
The CIG Community Workshop is being held online and will feature several keynote lectures, breakout groups and and discussion each day (see agenda). Talks will be recorded and posted on CIG’s youtube channel.
This summer I gave an online seminar as part of the Geophysics & Tectonics Seminar hosted by Keely O’Farrell at the University of Kentucky (seminar recording on youtube). In this seminar I present the hypothesis that strain-rate is an important factor in determining where earthquakes occur in subducting slabs, because strain-rate is a factor that affects the proposed triggering mechanisms for deep earthquakes.
Simulations of sinking tectonics plate provide new evidence that like earthquakes at the surface, deep earthquakes happen where the rate of deformation is the highest. The new results published in Sciences Advances show that in models with stiff (high viscosity) sinking plates, localized yielding occurs in regions of bending and buckling. The depth distribution of these fast deforming regions is very similar to the depth distributions of deep earthquakes.
A UC Davis new article by Becky Oskin provides a nice overview of the results.
I’m here in Washington, DC to attend the Finale meeting of the decade long science initiative funded by the Sloan Foundation to catalyze multi-disciplinary research into the cycling of carbon from the Earth’s surface into its interior. Subduction plays a key role in carrying carbon into the mantle. While most of that carbon comes back to the surface through arc volcanism, some of it may get subducted into the deep mantle (sometimes forming diamonds). Oliver Kreylos from UC Davis KeckCAVES has been collaborating with groups of DCO-related scientist to build tools to allow them to visualizae their unique data sets using head-mounted virtual reality hardware (e.g., VIVE). Oliver’s software infrastructure (VRUI) makes it possible for multiple scientists to simultaneously view and interact with a 3D digital data set (like a DEM of Montserratw with a volcanic gas cloud measured by drones). This VR tool enables scientists to intuitively explore the 3D structure, which facilitates more rapid understanding and building and testing of hypothesis.
Spent 2.5 days in Eugene, Oregon learning about data, experiments and numerical models of the subduction zone megathrust. The workshop was organized as part of the Modelling Collaboratory for Subduction. The key take-away for me was a “long-term” subduction modeler is that the long-term stress state in the subduction zone is a key parameter that is imposed in earthquake rupture dynamics simulations. So, carefully including the compositional and rheologic layers at the plate boundary interface in long term models will allow us to “hand” the stress state to models of earthquake rupture. The other key take away is that we really need to build basics models of small-scale process like porous media flow that are appropriate for asking questions related to the megathrust environment.
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.
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.
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.
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.