Earthquakes off the north Pacific Coast of the United States*

Epicenters of most of the larger earthquakes occurring off the coast of northern California and Oregon lie in two zones. One zone includes the north-facing submarine Gorda Escarpment, which extends nearly due west from Punta Gorda, and the south-facing Mendocino Escarpment as far offshore as long. 127° W. The other zone extends northwestward from the region of Cape Mendocino, indicating a linear extension of the San Andreas Rift zone as far as lat. 44° or 45° N.