seismo-, seism-, -seism, -seisms, -seisma, -seismically, -seismical, -seismal, -seismic
(Greek: to move back and forth; to shake, to move violently; earthquake)
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.).
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 "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.
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.
"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."
2. The geographic and historical distribution of earthquakes.
3. The likelihood of an area being subject to natural earthquakes.
2. The base of the seismogenic zone is the top of the more ductile asthenosphere (the ductile part of the earth just below the lithosphere, including the lower mantle which is about 180 km thick).
3. Capable of generating earthquakes.
Many of the world’s most disastrous earthquakes and volcanic eruptions take place at subduction zones, or areas under the ocean where one tectonic plate collides with another, sending sections of Earth’s crust down into the mantle.
The deep layers of seismic activity in these areas are called Wadati-Benioff zones and can be found as deep as 700 km.
Some areas are known to host parallel planes of seismicity referred to as double Benoiff zones, or DBZs, but these have been thought to be rare.
Analysis of global seismicity catalogs and characterization of the layer separation at 16 subduction zones revealed two parallel seismic strips, rather than a single broad zone, in most cases.
2. A record written by a seismograph in response to ground motions produced by an earthquake, explosion, or other ground-motion sources.
2. Any of various devices for measuring and recording the vibrations and intensities of earthquakes.
3. An instrument for recording automatically the phenomena of earthquakes.
A seismograph, or seismometer, is an instrument used to detect and record earthquakes. Generally, it consists of a mass attached to a fixed base. During an earthquake, the base moves and the mass does not. The motion of the base with respect to the mass is commonly transformed into an electrical voltage. The electrical voltage is recorded on paper, magnetic tape, or another recording medium.
This record is proportional to the motion of the seismometer mass relative to the earth, but it can be mathematically converted to a record of the absolute motion of the ground.
The term seismograph generally refers to the seismometer and its recording device as a single unit.