Images

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 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.

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.

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

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

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

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

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

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 spectrum is a curve showing amplitude and phase as a function of frequency or period, or how much of each type of shaking there is from an earthquake.

Station EMS in southern California.

The station refers to the place where a geophysical instrument is located.

A traveltime curve is a graph of arrival times, commonly P or S waves, recorded at different points as a function of distance from the seismic source. Seismic velocities within the earth can be computed from the slopes of the resulting curves. 

Turbidites (interbedded with mudstones/siltstones) from the Ross Sandstone Formation Turbidite system of Namurian age in County Clare, Western Ireland. The sandstone beds were formed in a deep basin by turbidites coming from a delta area.

A seismic refraction or seismic reflection line is a set of seismographs usually lined up along the earth's surface to record seismic waves generated by an explosion for the purpose of recording reflections and refractions of these waves from velocity discontinuities within the earth. The data collected can be used to infer the internal structure of the earth.

The reflection is the energy or wave from an earthquake that has been returned (reflected) from an boundary between two different materials within the earth, just as a mirror reflects light.

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.

The slip rate is how fast the two sides of a fault are slipping relative to one another, as determined from geodetic measurements, from offset man-made structures, or from offset geologic features whose age can be estimated. It is measured parallel to the predominant slip direction or estimated from the vertical or horizontal offset of geologic markers.