A reference to earthquakes or surface waves produced with acoustic or sonic energy for geophysical explorations of minerals, oil, etc.: "New seismic methods have become lucrative for oil companies."

"The seismic method was observed by a group of physicists who noticed that whenever an earthquake took place in Alaska then oil production in the Western Canadian Sedimentary Basin significantly increased because of the great waves of energy that moved at hundreds of meters a second were breaking apart rock formations that contained oil."

A section of a fault that has produced earthquakes in the past but is now quiet.

For some seismic gaps, no earthquakes have been observed historically, but it is believed that the fault segment is capable of producing earthquakes on some other basis; such as, plate-motion information or strain measurements.

An earthquake hazard which refers to anything associated with an earthquake that may affect the normal activities of people.

This includes surface faulting, ground shaking, landslides, liquefaction, tectonic deformation, tsunamis, and seiches (the sloshing of a closed body of water from earthquake shaking; including, swimming pools, ponds, lakes, etc.).

Seismic imaging directs an intense sound source into the ground to evaluate subsurface conditions and to detect high concentrations of contamination.

Receivers called geophones, analogous to microphones, pick up “echoes” that come back up through the ground and record the intensity and time of the “echo” on computers.

Data processing turns these signals into images of the geologic structure. This technology is similar in principle to active electromagnetic survey technology.

Here are more etails about seismic imaging.

A measure of the size of an earthquake based on the area of fault rupture, the average amount of slip, and the force that was required to overcome the friction sticking the rocks together that were offset by faulting. Seismic moment can also be calculated from the amplitude spectra of seismic waves.

A "slip" is the relative displacement of formerly adjacent points on opposite sides of a fault, measured on the fault surface.

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.

A reference to symmetrical fluctuations where the water-level rise is exactly equal to the water-level decline which is typical of standing waves set up on rivers, reservoirs, ponds, and lakes at a time that corresponds with the passage of seismic waves in other parts of the world.

An elastic wave generated by an impulse such as an earthquake or an explosion. Seismic waves may travel either along or near the earth's surface ("Rayleigh" and "Love" waves) or through the earth's interior ("P" and "S" waves).

Waves of Destruction

Earthquakes are said to radiate destruction much like bomb blasts in that seismic waves burst from the underground hypocenter (the point within the earth where an earthquake rupture starts; also known as the focus).

Surface waves consist of heaving waves produced by P and S waves. The P wave is the fastest wave which is generated by the fault rupture and it compresses and stretches the rock area. The S wave is slower but often the more destructive wave as it shakes rock from side to side.

• P waves, which compress and stretch rock, deliver the quake's initial thrust.
• Slower and often more destructive S waves follow, slithering side to side.
• S waves tear buildings off foundations and can churn wet soils into a mixture that acts like quicksand, causing buildings to tilt.
• At ground level, P and S waves produce surface waves that can flatten bridges, crack windows, or simply pass unnoticed.
• Eventually the waves weaken as they roll away from the hypocenter; but the seismic echoes of powerful quakes can resonate across and around the globe

A "Rayleigh wave" is a seismic surface wave causing the ground to shake in an elliptical motion, with no transverse, or perpendicular, motion.

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