Yakataga Gap, Alaska: Seismic History and Earthquake Potential

A 250-kilometer-long seismic gap in southern Alaska, which is situated along the boundary between the North American and Pacific plates, ruptured in two great earthquakes in 1899. Within the gap, earthquakes of moderate size form a ring of activity around a region of very low seismicity. The number of shocks of magnitude 6 or larger in this ring appears to have increased significantly since the 1958 earthquake, which occurred on the adjacent part of the plate boundary. This space-time pattern is similar to long-term patterns that preceded several large earthquakes in Japan. A shock of magnitude 7.7 on 28 February 1979 ruptured only a small part of the seismic gap. The remaining part, which already may have stored sufficient strain to generate a great shock, warrants intensive study to evaluate its potential for such an event.