Images

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

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

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).

A Love wave is a surface wave having a horizontal motion that is transverse (or perpendicular) to the direction the wave is traveling.

A magnetic polarity reversal is a change of the earth's magnetic field to the opposite polarity. This has occurred at irregular intervals during geologic time. Polarity reversals can be preserved in sequences of magnetized rocks and compared with standard polarity-change time scales to estimate geologic ages of the rocks.

Compare the fault area of the magnitude 7.3 (top) with that of the magnitude 5.6 (smallest one near the bottom).

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.

Liquefaction potential map of the San Francisco Bay Area, California. (Image courtesy of the Association of Bay Area Governments-ABAG)

The natural frequency is the frequency at which a particular object or system vibrates when pushed by a single force or impulse, and not influenced by other external forces or by damping. If you hold a slinky by one end and let it hang down and then give it one push up from the bottom, the rate of up-and-down motion is its natural frequency.

A diagram showing three stress types: tensional stress, compressional stress, and shear stress. 

Cross-section of the Earth with lithosphere, mantle, and the core divided into the metallic liquid core and the solid inner core.

En echelon shears crossing street, Hayward Hayward, California. The street shows en echelon shears crossing Foothill Boulevard in San Leandro, just to the north of Hayward. Here the shear zone is quite narrow.

A diagram showing the Earth's crust with continental and oceanic crust.

The crust is the outermost major layer of the earth, ranging from about 10 to 65 km in thickness worldwide. The uppermost 15-35 km of crust is brittle enough to produce earthquakes.

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

Acceleration, velocity, and displacement records. 

Displacement is the difference between the initial position of a reference point and any later position. The amount any point affected by an earthquake has moved from where it was before the earthquake.

When seismologists think of an earthquake, this image of a seismogram is what comes to their minds.

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)