S-waves do not pass through the earth's core, forming a Shadow Zone on the earth's side opposite from the epicenter.
A shadow zone is an area in which an S-Wave (secondary seismic wave) is not detected due to it not being able to pass through the core of the earth. When an earthquake occurs, seismographs near the epicenter, out to about 90° distance, are able to record both Primary and Secondary waves, but those at a greater distance no longer detect the S-wave. This is due to the fact that shear waves cannot pass through liquids. This was how Oldham proved that the Earth had a liquid outer core. The Moon has been proven by seismic testing to have a solid core, because it conducts shear waves. Shadowzone may refer to: Shadow zone, a secondary seismic wave Shadow Zone, the third album from the industrial metal band Static-X Shadow Zone (Axel Rudi Pell album) The oceanic oxygen minimum zone is sometimes referred to as a shadow zone. ... Cross section of the whole Earth, showing the complexity of paths of earthquake waves. ... Cross section of the whole Earth, showing the complexity of paths of earthquake waves. ... A type of seismic wave, the S-wave moves in a shear or transverse wave, so motion is perpendicular to the direction of wave propagation. ... Richard Dixon Oldham (July 31, 1858 – July 15, 1936) was a British geologist who, in 1906, argued that the Earth must have a molten interior as S waves were not able to travel through liquids nor through the Earths interior. ...
The S wave shadow zone occurs between 105 degrees and 180 degrees latitude (with the point of origin as zero and due south of origin as 180 degrees).
P-Waves (primary seismic waves) also have a shadow zone as they are refracted downwards on entering the Earth's core as the liquid outer core lowers their speed. This shadow zone occurs between 105 and 142 degrees. Plane P-wave Representation of the propagation of a P-wave on a 2d grid (empirical shape) Of the two types of elastic body waves (named because they travel through the body of the Earth) that are produced by earthquakes and recorded by seismometers. ...
"shadowzone," allowing any submarine positioned just beneath the dividing line between the warmer and cooler layers of water, to become invisible to sonar signals.
Columbus Iselin immediately recognized the significance of the acoustic shadowzone and the BT to submarine warfare.
A submarine equipped with a BT could use it to determine where the shadowzone lay in relation to the pursuing ship, thus becoming nearly invisible to an enemy sonar.
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