Images

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.

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

Moment = ? A D

? = shear modulus = 32 GPa in crust, 75 GPa in mantle

A = LW = area

D = average displacement during rupture

The New Madrid seismic zone in Central U.S.

A seismic zone is an area of seismicity probably sharing a common cause. 

A seismogram is a record written by a seismograph in response to ground motions produced by an earthquake, explosion, or other ground-motion sources.

A slab is the oceanic crustal plate that underthrusts the continental plate in a subduction zone and is consumed by the earth's mantle.

This turn-of-the-century wooden residence in Los Gatos sustained major damage when it moved off its foundation during the October 17, 1989, M7.1 Loma Prieta, California earthquake.

A surface wave is a seismic seismic wave that is trapped near the surface of the earth.

A tsunami is a sea wave of local or distant origin that results from large-scale seafloor displacements associated with large earthquakes, major submarine slides, or exploding volcanic islands.

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

Diagram of dip. Dip is the angle that a planar geologic surface (for example, a fault) is inclined from the horizontal.

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.

Alluvium visible in Salt River, Arizona (Photo by Sharon Reynolds, Arizona State University)

Cartoon of half-space model. A half space is a mathematical model used to approximate the earth when performing some calculations in seismology. The model is much simpler than the real earth.

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 .

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.

Sand ejected through a crack forming a series of sand boils along the railroad tracks adjacent to Deschutes Parkway in Olympia. 

Diagram of a locked fault showing the shortening and uplift at a coastline. A locked fault is a fault that is not slipping because frictional resistance on the fault is greater than the shear stress across the fault (it is stuck).

Refraction is (1) the deflection, or bending, of the ray path of a seismic wave caused by its passage from one material to another having different elastic properties. (2) bending of a tsunami wave front owing to variations in the water depth along a coastline.

The residual is the difference between the measured and predicted values of some quantity.