PASADENA, Calif. — Shattered cave formations in the central United States may preserve one of the longest records of powerful earthquakes in this region. Historical records from European settlers provide vivid accounts of deadly earthquakes in states such as Missouri, Tennessee and Illinois. For instance, in 1811 and 1812, people saw the ground ripple like ocean waves when the New Madrid Fault Zone unleashed earthquakes thought to be greater than magnitude 8. However, no written accounts exist from before Europeans arrived. And most earthquake faults in the Midwest are hidden deep beneath the surface, so scientists can't dig into the...