Paul VoosenMany of the world’s most dangerous earthquake faults are a silent menace: They have not ruptured in more than a century.
To gauge the hazard they pose to buildings and people, geologists cannot rely on the record of recent strikes, captured by seismometers.
Instead, they must figure out how the faults behaved in the past by looking for clues in the rocks themselves, including slickenlines, scour marks along the exposed rock face of a fault that can indicate how much it slipped in past earthquakes.Now, researchers in New Zealand say slickenlines, when curved, can also reveal which end of a fault slipped first. “This is important information to know,” says Jean Paul Ampuero, a seismologist at the California Institute of Technology.