Images

Diagram showing the epicenter and hypocenter. 

The epicenter is the point on the earth's surface vertically above the hypocenter (or focus), point in the crust where a seismic rupture begins.

Strike-slip, normal, and reverse faults. A reverse fault with a small dip angle is called a thrust fault.

Photo of fault gouge. Fault gouge is crushed and ground-up rock produced by friction between the two sides when a fault moves.

Fault plane diagram. (Image courtesy of Kian H. Chong, Univ. of California, Davis)

Fault scarp produced by the M7.1 Hector Mine, Calfornia earthquake. (Photo by Ken Hudnut, U.S. Geological Survey)

Focal mechanism examples. A fault plane solution is a way of showing the fault and the direction of slip on it from an earthquake, using circles with two intersecting curves that look like beach balls. Also called a focal-mechanism solution.

First motion mechanism. On a seismogram, the first motion is the direction of ground motion as the P wave arrives at the seismometer. Upward ground motion indicates an expansion in the source region; downward motion indicates a contraction.

Liquefaction and lateral spreading occurred along the west side of Sunset Lake trailer park in Tumwater.

Plot showing 440 Hertz and 880 Hertz. Hertz (Hz) is a unit of measurement named in honor of Heinrich Hertz, the German physicist who in 1887 first produced electromagnetic waves. Expresses the frequency in cycles per second; 1 Hz = 1 cycle of rise and fall of a wave per second .

Map showing intensity for the New Madrid earthquake. (Image courtesy of the Central U.S. Earthquake Consortium)

The earthquakes (colored dots) in the middle of the continent are intraplate events. Those near the ocean boundary are at the boundary between two plates (interplate).

Iceland and plate motions. Kinematic refers to the general movement patterns and directions of the earth's rocks that produce rock deformation.

Photo of a Kinemetrics FBA-23 accelerograph. The device is black and square with rounded edges on a green background.

This image of the Los Angeles region combines this information to predict the total amplification expected in future earthquakes from local geologic conditions or site effects.

A diagram depicting the tectonic components of a volcanic arc, including the back arc spreading center, back arc convection cell, zone of fractional melting, outer arc trough, outer arc ridge, subducting oceanic lithosphere, and asthenosphere.

An illustration depicting an asperity (pink blob) on fault surface (yellow parallelogram). 

A diagram showing a slice of the Earth's lithosphere, including continental crust, oceanic crust, asthenosphere, and the upper mantle.

An illustration showing two stick figures doing basement excavations, one with a frown that excavated into the labelled hard, stable bedrock on the left and the other with a smile that excavated above the labelled bedrock surface.  

Cross-section of the Benioff zone resulting from a by the interaction of a downgoing oceanic crustal plate with a continental plate.

A diagram of a blind thrust fault resulting in ductile rock layers folding over the fault and leaving the fault under the surface.

A sketch of the thinner crust and thicker mantle. The crust and top portion of the mantle are labelled "Lithosphere "strong'" and the bottom portion of the mantle (bottom) labelled "Asthenosphere "weak.'"