PETER J. SMITH Department of Earth Sciences Open University Milton Keynes, U.K. The three largest earthquakes over the past 150 years in the San Francisco Bay area (1868, 1906, 1989) were all preceded by several decades of high activity in moderate (magnitude 5.0 to 5.9) earthquakes on surrounding faults, and followed by low levels of such activity. If the level of moderate earthquake activity is low over the next few years, another large shock is unlikely to occur for at least a decade. If

PETER J. SMITH Department of Earth Sciences Open University Milton Keynes, U.K. The most seismically active zone in the central/eastern United States is the New Madrid, Mo., area, where in 1811-12 the three largest known intraplate earthquakes occurred. Because a recurrence of such events would be a disaster, an understanding of the New Madrid zone is urgently needed. A new analysis shows that most earthquakes in the region correlate with the Blytheville and Pascola arches within the Reelfoo