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June 2017 John Chen organised the first meeting of the EarthScope Oceans Steering Comittee at the beautiful campus of SUSTech (China's upcoming rival of MIT, see also below) in Shenzhen, an hour north of Hongkong. See here for a brief report on the meeting.
June 2017 I have been appointed adjunct professor at the Southern University of Science and Technology in Shenzhen (China) for the next five years and will spend some time in their brand new Oceanography department, which is led by Yongshun (John) Chen, every year.
November 2016 The last of the nine Mermaids that we launched in 2014 around the Galapagos islands has transmitted its final seismogram. These Mermaids were based on the classical Argo floats that have limited battery capacity, the average lifespan of our floats was one and a half years. But they have clearly shown that the concept of floating seismometers works. The second generation Mermaids, with a lifespan of five or more years has now been developed with our industrial partner OSEAN in Le Pradet (France) and is being tested by us. The figure shows the locations of the Mermaids transmitting seismograms of P, pP and PKP waves (PKP goes deep enough that it traverses the Earth's core). We have started to analyze the data and expect to show first images of the mantle beneath Galapagos at the AGU Meeting in New Orleans, December 2017.
April 2015: Geoazur and Princeton celebrated my career, and it was heartwarming to see so many old faces back in my (relatively) new environment at the Cote d'Azur. Click here for some photos and to read my views on the future of the geosciences and what that means for the way we educate students.
September 2014: Retirement... I must have broken some records, since I turn 69 this month and French law stipulates retirement at the age of 65, with the possibility to extend this three times for a year. However, even if I stop teaching, I'll keep my office as emeritus, and my door is open if you want to talk to me. I am also looking forward to spend again more time at Princeton, where I have been emeritus since 2008...
June 2014: With Sergei Voronin we worked at methods to reduce the size of the the massive tomographic matrices used in finite-frequency tomography, such as to avoid adjoint methods that are much more expensive computationally. By chance we stumbled upon a way to estimate the errors in the data in an objective way, using the fact that at least part of the data used in tomography are highly redundant, even if the system itself is underdetermined. Click here to request an offprint.
With Diego Mercerat we show that cross-correlation travel times vary linearly with variations in the Earth's elastic parameters for changes of up to +/-10%. There is thus no need for nonlinear iterations for much of the mantle. Click to request an offprint.
LECTURE: At a Meeting of the European Seismological Commission n Montpellier (France) I gave my view on where global seismic tomography is heading. Click here for a video and/or a PDF version of my talk.
By now the debate on Banana-doughnut kernels for seismic tomography is a little old, most seismologists accept that we have to use finite frequency methods if we wish to make any progress. But I keep the link because it is still a much-requested item.
Want to learn about finite-frequency tomography? If you do not wish to spend fifty pounds on the book, but also lack the courage to digest all 194 equations in Dahlen, Hung and Nolet (2000), then try this tutorial paper (click on the image).