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A velocity structure is a generalized regional model of the earth's crust that represents crustal structure using layers having different assumed seismic velocities.

YBP is an abbreviation for "years before present".

Formation of Earth: 4.6x10^9 YBP

Dinosaur extinction: 6.5x10^7 YBP

First hominids: 2x10^6 YBP

Last great ice age: 1x10^4 YBP

Declaration of Independence: 2x10^2 YBP

Establishment of UWB: 1x10 YBP

High, medium, and low amplitude. The amplitude is the size of the wiggles on an earthquake recording.

Ripples on a pond are attenuated as they move away from the source. When you throw a pebble in a pond, it makes waves on the surface that move out from the place where the pebble entered the water. The waves are largest where they are formed and gradually get smaller as they move away. This decrease in size, or amplitude, of the waves is called attenuation.

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

If you were to stand on the fault and look along its length, this is a type of strike-slip fault where the right block moves toward you and the left block moves away.

Snapshots of a rupture front moving across a fault surface. 

An S wave, or shear wave, is a seismic body wave that shakes the ground back and forth perpendicular to the direction the wave is moving.

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.

The standard deviation is how much a set of data is different from the curve it should make when plotted on a graph. Or, the square root of the average of the squares of deviations about the mean of a set of data. Standard deviation is a statistical measure of spread or variability.

Station EMS in southern California.

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

When the force trying to make the block (m) slip becomes greater than the frictional force causing it to stick, the block will slip.

The dots on the left make a regular pattern, but the dots on the right make a random, or stochastic, pattern.

Strain is the small changes in length and volume associated with deformation of the earth by tectonic stresses or by the passage of seismic waves.

The strike is the trend or bearing, relative to north, of the line defined by the intersection of a planar geologic surface (for example, a fault or a bed) and a horizontal surface such as the ground.

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.

Subduction zone of the Juan de Fuca Plate and North America Plate, creating the Mt. St. Helens and Mt. Hood volcanoes.

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

A sand boil is sand and water that come out onto the ground surface during an earthquake as a result of liquefaction at shallow depth.

Secular refers to long-term changes that take place slowly and imperceptibly. Commonly used to describe changes in elevation, tilt, and stress or strain rates that are related to long-term tectonic deformation.