Images

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.

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.

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.

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

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.'" 

A diagram with 3 yellow squares with arrows pointing to indicate steps. The first step is labelled "Time 1: pure parent isotope," the second step is labelled "After 1 half life: 1/2 parent and 1/2 daughter isotope," and the third step is labelled "After 2 half lives: 1/4 parent and 3/4 daughter isotopes." 

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