Waves to images - Jeroen Tromp is creating a map of the Earth’s interior, which is composed of layers of iron and nickel, flowing liquids, and tectonic plates that combined are nearly 4,000 miles thick. Scientists study the Earth’s interior by measuring ground motions on the planet’s surface, explains Tromp, a professor of geology and applied and computational mathematics.
Jeroen Tromp, Ebru Bozdag, James Smith, Wenjie Lei, and Shravan Hanasoge attended the CIG/QUEST/IRIS joint workshop on seismic imaging of structure and source from the 14th to 17th of July in Fairbanks, Alaska.
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.
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 region1, 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 area13, 14, or low in resolution, and thus miss the finer-scale details of mantle structure5, 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
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.
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Seismology Research Group attends Quest II Workshop in Hveragerdi, Iceland
Jeroen Tromp, Daniel Peter, Shravan Hanasoge, and Ebru Bozdag attended the 2nd QUEST (QUantitative Estimation of Earth's Seismic Sources and STructure) workshop from 12th to 19th of July in Hveragerdi, Iceland. The QUEST project is an Initial Training Network funded by European Commission (www.quest-itn.org). It is dedicated to the memory of Albert Tarantola with a focus on all aspects of computational seismology and source & structural inverse problems. During the one-week workshop there was also a one and a half day field trip to the Western and Eastern volcanic zones and to the south Icelandic seismic zone. During the field trips the following notable geological features were explored: Nesjavellir geothermal area, Hengill volcanic system, Þingvellir graben and fissure swarm, Geysir geothermal area, Gullfoss waterfall, Kerið crater, 1912 fault rupture at Selsund, Hekla volcano, Ljótipollur and Vatnaöldur Veiðivötn eruptive fissures, Landmannalaugar and Torfajökull volcano. More information can be found at www.quest-itn.org/events/2nd-quest-workshop. Photos by Ebru Bozdag