Infos scientifiques
C'est quoi l'échelle de Richter ?
22 February 2011 Last updated at 12:44 ET There are thousands of earthquakes around the world each year, but only a few cause serious damage. The figures above seek to measure an earthquake in terms of the energy it releases. The scale used to measure earthquakes is unusual. For example, the difference in strength between an earthquake of magnitude 5 and magnitude 6 earthquake is much more dramatic than a rise of just one unit would suggest.
Pourquoi ce séïsme
Seisme-au-japon épicentre Le séisme qui vient de survenir au Japon - lire ici une note avec les premières informations - s'explique par la tectonique des plaques. Le Japon fait face à une menace sismique (et volcanique) importante et quasi permanente à l'échelle des temps géologiques. La cause en est connue, l'archipel japonais se situe à la frontière de trois plaques tectoniques : les plaques Pacifique, eurasienne et des Philippines dont les interactions en font l'une des zones les plus actives de la planète. Surtout « la plaque Pacifique glisse sous le Japon à une vitesse de 8 cm par an », m'explique au téléphone Xavier Le Pichon , Professeur honoraire au Collège de France qui a conduit des études dès les années 1980, avec le sous marin de l'Ifremer le Nautile , sur les zones de failles. Depuis leur laboratoire du CEREGE , à Aix en Provence, Pierre Henry poursuit les explications.8 vidéos en ce moment Toutes les vidéos info (11094) Baptême pour adultes : témoignages EXTRAIT - 2min 03s
Les explications d'un sismologue
COMET - Centre for the Observation and Modelling of Earthquakes and Tectonics | Homepage
John Elliott, Zhenhong Li, Richard Walters, Barry Parsons COMET+ researchers are investigating the ground deformation associated with the recent Yushu earthquake using satellite radar measurements. They intend to model the distribution of subsurface slip in order to improve our understanding of faulting and seismic hazard Background On the 13th April 2010, a magnitude 6.9 earthquake struck the relatively remote region of Western China, in the county of Yushu at the eastern end of the Tibetan Plateau at about 4000 m elevation. Despite the low population density, approximately 2200 are thought to have died in this event, with over 10,000 injured.The magnitude 8.9 earthquake that struck Friday off the coast of Japan "is going to be among the top 10 earthquakes recorded since we have had seismographs," said seismologist Susan Hough of the U.S. Geological Survey in Pasadena. "It's bigger than any known historic earthquake in Japan, and bigger than expectations for that area." Geologists had expected the portion of the Pacific "Ring of Fire" that produced this quake to yield a temblor on the order of magnitude 8 or perhaps 8.5, she said. "Something as big as an 8.9 is a bit of a surprise," she said. A quake that big usually requires a long, relatively straight fault line that can rupture, such as those found in Peru and along the eastern coast of South America.
