Issues

A small river snakes its way through the local landscape, documenting geologic processes at work. This aerial view of the San Andreas Fault in the Carizzo Plain (California) illustrates localized long-term deformation and short-term erosion at the plate-boundary between the North American and Pacific plate. The linear trace of the San Andreas Fault is flanked by small hills (called pressure ridges) created by the fault’s movement over millions of years. The power of water even in small creeks creates these deflected river channels crossing the fault. Geoscientists use measurements of river bed offsets to infer fault motion. The article “New Insights on Subsurface Geology and the San Andreas Fault at Loma Prieta, Central California” (this issue) examines the deep geologic structure of the San Andreas Fault about 250 km north of the Carizzo Plain in context of the 1989 magnitude M 6.9 Loma Prieta earthquake.

Image credit: Kip Evans/Alamy Stock Photo