Page 50

RA2012_en

Probing the Earth The seismic noise generated by ocean swell and other novel research methods shed light on the internal dynamics of our planet and its turbulent past. New geosciences facility on the French Riviera CNRS’s strategy consists as much as possible in bringing together, in one location, all units dedicated to the same discipline that were previously dispersed or isolated. In 2012, in the Provence-Alpes-Côte d’Azur region, the Center for Prehistory, Antiquity and Middle-Ages Studies (CEPAM) was integrated into the Institute for Human Sciences in Nice. The vacant facility was then restructured to house the metropolitan teams of the Géoazur research unit, which were spread across four sites. Following asbestos removal, 4,217 m2 were rehabilitated in 2012 at a total cost of about €5 million and delivered in early 2013. 48 One quake can trigger another On April 11, 2012, a magnitude 8.7 earthquake ruptured the seafloor beneath the Indian Ocean. Two hours later, a second quake with a magnitude of 8.2 followed. Geophysicists have shown that these quakes were the result of the 2004 Banda Aceh megathrust earthquake. Using a post-seismic relaxation model that takes into account the viscosity of the mantle, they were able to show that the stresses caused by the megathrust earthquake continued to grow for several years before triggering the 2012 quakes. Nature September 2012 online A study has shown that between 100 and 200 million years after its formation, the Earth was made up of an ocean of molten magma. SUNDA ISLANDS INDIA SOMALIA ARABIA AUSTRALIA EURASIA Central Indian Basin Wharton Basin Traces of the primordial magma ocean discovered The presence of 3.4 billion-year-old rocks in Greenland support the hypothesis that between 100 and 200 million years after its formation, the Earth was made up of an ocean of molten magma which gradually cooled, forming the crust and the continents. Now, a French-Danish team of geochemists has measured in these rocks a deficit of neodymium-142, a key chemical element for the study of the Earth’s formation, revealing the existence of primordial inhomogeneities consistent with the crystallization of a magma ocean. Nature October 2012 online Simplified tectonic map of the April 2012 quake area. The April earthquakes (yellow stars) occurred near the site of the 2004 Banda-Aceh earthquake (red star). The arrows show the motion of the plates in relation to Eurasia (approximately 5 centimeters per year off the coast of Sumatra). A year at CNRS 2012


RA2012_en
To see the actual publication please follow the link above