"Provocative analysis of sea-floor cores suggests that quakes on the Cascadia fault off California can trigger tremors on the San Andreas." A controversial study argues that at least eight times in the past 3,000 years, quakes made a one-two punch off the west coast of the United States. A quake hit the Cascadia fault off the coast of northern California, triggering a second quake on the San Andreas fault just to the south. In some cases, the delay between the quakes may have been decades long. The study suggests that Cascadia, which scientists think is capable of unleashing a magnitude-9 earthquake at any time, could set off quakes on the northern San Andreas, which runs under the San Francisco Bay Area. Several earthquake scientists told Nature that more work is needed to confirm the provocative idea. Researchers have long considered the two faults seismically separate. Chris Goldfinger, a geologist and palaeoseismologist at Oregon State University in Corvallis, will present the