Ground shaking caused by the sudden release of accumulated strain by an abrupt shift of rock along a fracture in the earth or by volcanic or magmatic activity, or other sudden stress changes in the earth.
A program of studies with instruments to provide accurate and timely data and information on seismic events, including their effects on buildings and structures, employing modern monitoring methods and technologies.
The USGS Seismological Laboratory in Albuquerque installs and maintains a world network of seismograph stations, collects the seismic data, and evaluates seismic instruments. Site includes links to ASL publications, earthquake maps and seismic data.
Information on earthquakes in central California and the San Francisco region with links to four types of field studies, deep seismic investigations, geotechnical investigations, shallow seismic imaging, and airborne geophysical surveys.
Photographic archive collection from the USGS Photo Library. Photos dated 1868-1992 are of geology, earthquake damage, national parks, pioneer photographers, St. Helens eruption and mining and available at 100, 700 and 1400 dots/inch resolution.