Princeton University

Hosted by the Princeton Plasma Physics Laboratory

Official Website: http://www.pppl.gov/events/colloquium-seismic-imaging-and-inversion-based-spectral-element-and-adjoint-methods

Professor Jeroen Tromp, The Department of Geosciences, Princeton University

TIME and LOCATION: February 6, 2013, 4:15pm to 5:30pm, Princeton Plasma Physics Laboratory, MBG Auditorium

Harnessing high-performance computers and accurate numerical methods to better constrain physical properties of Earth's interior is rapidly becoming one of the most important research topics in exploration and global seismology. We use spectral-element and adjoint methods to iteratively improve 3D subsurface images ranging from exploration to global scales. The spectral-element method, a high-order finite-element method with the advantage of a diagonal mass matrix, is used to accurately calculate three-component synthetic seismograms in complex 3D Earth models.

Three miles from the main campus, Princeton’s high-performance computers hum undisturbed, cranking out projections of what happens when a neutron star encounters a black hole — things don’t go well for the neutron star — working out how trees know when it is safe to put out their spring leaves, and designing drug candidates for treating inflammatory diseases.

The researchers — based in the laboratory of Jeroen Tromp, the Blair Professor of Geology in Princeton’s Department of Geosciences — simulated the meteorite strike that caused the Chicxulub crater in Mexico, an impact 2 million times more powerful than a hydrogen bomb and widely thought to have triggered the mass extinction of the dinosaurs 65 million years ago. The team’s rendering of the planet showed that the impact’s seismic waves would be scattered and unfocused, resulting in less severe ground displacement, tsunamis, and seismic and volcanic activity than previously theorized.

Photo: The Princeton model (Image courtesy of Conor Myhrvold)

Princeton University and Princeton Plasma Physics Laboratory researchers Jeroen Tromp (Geosciences), Emily Carter, Choong-Seock Chang, and William Tang are among the recipients of the Department of Energy’s 2013 Innovative and Novel Computational Impact of Theory and Experiment (INCITE) multi-year awards totaling 265 million core hours on Oak Ridge National Laboratory’s Cray XK7 “Titan” and Argonne National Laboratory’s IBM Blue Gene/Q “Mira.”

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The goal here is to bridge the gap between these two types of inversion by simultaneously fitting frequency-dependent phase anomalies of numerous body and surface waveforms in complete three-component seismograms, thereby effectively using entire seismographic records.

Authors: Hejun Zhu, Ebru Bozdağ, Daniel Peter, & Jeroen Tromp

Abstract: Images of the European crust and upper mantle, created using seismic tomography, identify the Cenozoic Rift System and related volcanism in central and western Europe. They also reveal subduction and slab roll back in the Mediterranean–Carpathian region^{1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12}. However, existing tomographic models are either high in resolution, but cover only a limited area^{13, 14}, or low in resolution, and thus miss the finer-scale details of mantle structure^{5, 12}. Here we simultaneously fit frequency-dependent phase anomalies of body and surface waveforms in complete three-component seismograms with an iterative inversion strategy involving adjoint methods, to create a tomographic model of the European upper mantle. We find that many of the smaller-scale structures such as slabs, upwellings and delaminations that emerge naturally in our model are consistent with existing images. However, we also derive some hitherto unidentified structures. Specifically, we interpret fast seismic-wave speeds beneath the Dinarides Mountains, southern Europe, as a signature of northeastward subduction of the Adria plate; slow seismic-wave speeds beneath the northern part of the Rhine Graben as a reservoir connected to the Eifel hotspot; and fast wave-speed anomalies beneath Scandinavia as a lithospheric drip, where the lithosphere is delaminating and breaking away. Our model sheds new light on the enigmatic palaeotectonic history of Europe.

Nature Geoscience 5, 493–498 (2012) doi:10.1038/ngeo1501 Received: 16 November 2011 | Accepted: 21 May 2012 | Published online: 24 June 2012. URL: http://www.nature.com/ngeo/journal/v5/n7/full/ngeo1501.html

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Printable version as it appeared in the Princeton Plasma Physics Laboratory Weekly

Photo caption: Princeton scientists (from left) Venkatramani Balaji, Jeroen Tromp and William Tang — shown at the Visualization Laboratory created by the Princeton Institute for Computational Science and Engineering — have received funding from the Group of Eight's Research Councils Initiative on Multilateral Research Funding to support their work using exascale supercomputing technology. (Photo by Elle Starkman)

Postdoctoral researchers Shravan Hanasoge of Princeton's Department of Geosciences and Michael Kesden of NYU's Center for Cosmology and Particle Physics simulated the visible result of a primordial black hole passing through a star. Theoretical remnants of the Big Bang, primordial black holes possess the properties of dark matter and are one of various cosmic objects thought to be the source of the mysterious substance, but they have yet to be observed.