Images

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.

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.

Diagram of dipping slab with different focal depth events. The focal depth refers to the depth of an earthquake hypocenter.

Small foreshocks on a seismic record. Foreshocks are relatively smaller earthquakes that precede the largest earthquake in a series, which is termed the mainshock. Not all mainshocks have foreshocks.

Diagram of frequency. The frequency is the number of times something happens in a certain period of time, such as the ground shaking up and down or back and forth during an earthquake.

Geodesy is the science of determining the size and shape of the earth and the precise location of points on its surface.

The geologic time scale showing each eon, era, period, epoch, and their associated ages.

Photo of the Grand Canyon located in Grand Canyon National Park, Arizona, Untied States.

Diagram of great circle. The shortest path between two points on the surface of a sphere lies along a great circle.

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)

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

Diagram of left-lateral motion on fault. If you were to stand on the fault and look along its length, this is a type of strike-slip fault where the left block moves toward you and the right block moves away. See also right-lateral. 

Photo of a leaning transmission tower being held up by lifelines. Lifelines are structures that are important or critical for a community to function, such as roadways, pipelines, powerlines, sewers, communications, and port facilities.

Lithologic cross-section example with descriptions of lithology at different depths. 

The Landers fault (red lines at left) and the Hector Mine fault and its aftershocks (red lines and circles at right). The Hector Mine earthquake was a magnitude 7.1, and it produced thousands of aftershocks.

A P wave, or compressional wave, is a seismic body wave that shakes the ground back and forth in the same direction and the opposite direction as the direction the wave is moving.

Person sitting and overlooking valley of snow-topped mountains with clouds in between mountains 

Diagram of period.  The period is the time interval required for one full cycle of a wave.

Plate Tectonics is the theory supported by a wide range of evidence that considers the earth's crust and upper mantle to be composed of several large, thin, relatively rigid plates that move relative to one another. Slip on faults that define the plate boundaries commonly results in earthquakes.