Two important local geologic factors that affect the level of shaking experienced in earthquakes are (1) the softness of the surface rocks and sediments and (2) the thickness of surface sediments. This image of the Los Angeles region shows the softness of near-surface rocks and sediments. By "softness" we really mean the speed at which shear waves travel in the upper 100 feet of a site.

Data for image courtesy of Chris Wills, California Division of Mines and Geology. Map created by Ned Field.

Cooperating Organizations