* Two previously unknown faults in the Puget Sound region ruptured at about the same time 1,100 years ago, according to a new study, offering clues to a potentially double earthquake threat.

*The study, published in the journal _Science Advances_, found that the South Whidbey Island fault and the Seattle fault ruptured within a few decades of each other, generating combined shaking greater in magnitude than previously estimated for either fault alone.

*The findings suggest that the two faults could rupture together again, producing devastating consequences for the region including major damage to buildings and infrastructure, widespread power outages, and the potential for landslides and tsunamis.

*Scientists say the findings could help them better assess the earthquake risk in the Seattle area, which is home to more than 4.5 million people and is considered one of the most vulnerable regions to a large earthquake in the United States.