The big one lurking beneath LA

 作者:纪诱     |      日期:2019-03-08 05:01:19
By Jeff Hecht in Boston A LARGE and active fault is lurking beneath the centre of Los Angeles, geologists have discovered. The fault previously escaped detection because it is nearly horizontal, tilting at only about 25 degrees, and does not reach the surface. In Science (vol 283, p 1516), John Shaw of Harvard University and Peter Shearer of the Scripps Institution of Oceanography in La Jolla, California, blame a partial rupture of the fault for the magnitude 6.0 Whittier Narrows quake in 1987. Once every 500 to 2000 years, the fault, which is the first to be found directly under the city’s centre, could unleash a devastating quake of 7.0 magnitude. The fault could also explain a curious gap in the complex geology of the Los Angeles basin. Satellite measurements show the area is being compressed along a north-south axis by 7 to 8 millimetres a year,