Images

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.

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

Illustration of Isaac Newton sitting under an apple tree, a reference to the well-known story of the epiphany Newton had when an apple fell on his head and lead to him discovering gravity.

Photo of Zion Canyon located in Zion National Park in Utah, United States. (Image courtesy of Justin Gould)

Photo of GPS site with instrument on a tripod and a solar panel. (Photo by John Galetzka, U.S. Geological Survey)

Photo of bridge.  Geotechnical means referring to the use of scientific methods and engineering principles to acquire, interpret, and apply knowledge of earth materials for solving engineering problems.  

Horst and graben diagram. A graben is a down-dropped block of the earth's crust resulting from extension, or pulling, of the crust. 

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

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.

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).

Plot showing least squares fit. When plotting data points on a graph, the least-squares-fit is the line or curve that comes closest to going through all the points.

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).

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).

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.

Ripples on a pond are attenuated as they move away from the source. Q is the inverse of attenuation. A high Q means a low attenuation.

Geologic time scale showing eras, periods, and notable events in terms of millions of years ago.