earthquakes shake water out of wet soil, new research suggests. Since the San Francisco earthquake of 1906, the observation that streams carry more water following a quake has baffled geologists. Some experts propose that earthquakes compress the water-bearing rocks that naturally feed streams, wringing more water from them. Others maintain that quake movements expand these aquifers, riddling them with cracks through which water seeps out. Neither explanation is true, assert Michael Manga and colleagues from the University of California, the us.

Their study of the Sespe Creek in the us indicates that surface soil, not rocks, gives up its water and that it does so in response to shaking, rather than squashing or stretching. "When you shake soil, pores containing water become compact and you squeeze out a little bit of water,' explains Emily Brodsky, one of the researchers.