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AGU Fall Meeting 2018


The largest geophysics conference in the world will be held in Washington DC this year. I'll be there presenting some new results on North American lithospheric structure - see abstract below. 

If you are a prospective student or post-doc (or simply interested in chatting about fun science) attending AGU then I encourage you to get in touch with me; I would be happy to make time to meet with you. 

In case you're interested, here are some sessions that I will be following with alert interest and great concern (in no particular order):

DI003 Advances in Understanding Earth's Dynamic Processes using Seismic Anisotropy 

DI005: A Unified View on the Composition, Structure and Dynamics of the Lithosphere

DI015: Interdisciplinary Perspectives on Silicate Melting from Source to Surface

DI021: The Physical Origin of Geophysical Anomalies

T012: (De-)Cratonization Dynamics

T040: Structure and dynamics of the upper mantle: characterizing the lithosphere-asthenosphere system from crust to transition zone

T031 Observations and models of multiphase deformation in rifts and rifted margins

T032 Oceanic Lithosphere: Structure and Evolution from Creation to Destruction

T044 Synthesis: Knowns and Unknowns of the Cascadia Subduction Zone

T055: Wyoming Craton: From Precambrian core of Laurentia to current state within North America

S007: Emerging Science from the EarthScope Transportable Array in Alaska and Canada

- S011: Frontiers of Uncertainty Quantification in Geoscientific Inversion

 


The deep structure of North American lithosphere illuminated by complementary seismic data types
Zachary Eilon, Karen M. Fischer, Colleen A. Dalton

The internal structure of continental lithosphere holds the key to our understanding of plate tectonic cycles and the long-term stability of cratons. Detailed imaging of the upper mantle has the potential to reveal chemical alteration, deformation fabric, thermal structure, and melt distribution, providing not only a contemporary snapshot but also an integrated history of the interactions between the Earth’s surface and its deep interior. We apply a transdimensional, hierarchical Bayesian inversion parameterised using piecewise discontinuous splines to solve for 1-D radially anisotropic shear velocity models of crust and upper mantle beneath long-lived stations across North America. The advantages of a Bayesian approach include quantitative uncertainty estimation and the ability to modularly incorporate multiple data types; we use Rayleigh wave and Love wave phase velocities from earthquakes and ambient noise, Rayleigh wave ellipticity ratios, and both P-sandS-pconverted phases. Taken jointly, this combination of data types provides excellent constraints on absolute velocities, crustal structure, and sharp gradients in velocity within or at the base of the lithosphere. We find that S-pphases are essential to capture accurately the characteristics of deep velocity gradients, such as those seen widely but discontinuously in the cratonic mid-lithosphere. Observed structures include shallow melt and adiabatic geotherms immediately beneath thin lithosphere in portions of the western US, as well as intra-lithospheric low-velocity zones beneath the cratons that have amplitude and depth consistent with new data on exotic lithologies associated with subduction-derived fluid reaction products. 

Non-specialist/jargon version:  At the heart of many continents lie large regions of the Earth’s tectonic plates that appear to be much older than their surroundings. We don’t yet understand how these stable regions were formed billions of years ago, or exactly why they are so resistant to being broken up or squished into mountains as vast forces act upon them. Here we use a new combination of types of seismic waves – Earth vibrations set off by distant earthquakes – to assess the properties of these ancient continental regions and the younger, weaker material that surrounds them. Different types of seismic waves are good for pinpointing certain individual properties of the Earth; by taking into account the information from multiple data types simultaneously, we can get a much better understanding of the internal structure of the tectonic plates and try to answer questions about how they were produced and how they have evolved – or not – over time.

 

 

 

Earlier Event: November 9
Invited talk at CalTech department seminar