Sharp Boundary Between Lithosphere and Asthenosphere

Friday, July 29, 2005 in Earthquakes, Seismology and Geophysics by Dave Schumaker | 1 comment

A graduate student at Brown University has published a paper showing that there is a sharp divide between the lithosphere (the rigid upper crust that we live on) and the asthenosphere (a pliable layer), according to data gathered from various seismic networks. Catherine Rychert and colleagues discovered that sound waves recorded by the sensors slow considerably about 90 to 110 kilometers below ground – a sign that the rock is getting weaker and that the lithosphere is giving way to the asthenosphere. Within in a distance of a mere 11 kilometers – roughly 7 miles or less – the transition is complete. This evidence runs contrary to the prevailing notion that the lithosphere-asthenosphere transition is a gradual one. It also points up the fact that temperature alone cannot define the boundary.