Seismic shadow zone (from USGS)

Seismic shadowing is a global effect of an earthquake. The seismic waves generated by an earthquake pass through the body of the Earth, but between 104° and 140° from the focus of an earthquake, little or no seismic waves can be detected. This is because primary waves (P-waves) are refracted by the Earth's core and secondary waves (S-waves) are stopped by the core. Image File history File links No higher resolution available. ... Image File history File links No higher resolution available. ... The United States Geological Survey (USGS) is a scientific agency of the United States government. ... This article is about the natural seismic phenomenon. ... Body waves and surface waves Earthquake wave paths p-wave and s-wave from seismograph A seismic wave is a wave that travels through the Earth, most often as the result of a tectonic earthquake, sometimes from an explosion. ... This article is about Earth as a planet. ... The hypocenter or hypocentre (literally: below the center from the Greek υπόκεντρον), may refer to the site of an earthquake or to that of a nuclear explosion. ... Plane P-wave Representation of the propagation of a P-wave on a 2d grid (empirical shape) One 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. ... The planetary core consists of the innermost layer(s) of a planet. ... 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. ...

When an earthquake occurs, seismic waves radiate out spherically from the earthquake's focus. When the waves reach the Earth's surface, a seismograph can detect the movement of the rock. The velocity of the waves is dependant on the density of the rock that the waves pass through. The density changes abruptly at the boundary between the Earth's solid mantle and liquid core, causing the P-wave wavefront to change direction and the S-waves to stop entirely. The hypocenter or hypocentre (literally: below the center from the Greek υπόκεντρον), may refer to the site of an earthquake or to that of a nuclear explosion. ... Seismographs (in Greek seismos = earthquake and graphein = write) are used by seismologists to record seismic waves. ... For other uses, see Density (disambiguation). ... Earth cutaway from core to exosphere. ... The planetary core consists of the innermost layer(s) of a planet. ...

P-waves are refracted by the Earth's core, but can still travel through the core to the other side of the Earth. The P-wave shadow zone extends from 104° away from the focus, to 140°.

S-waves are unable to pass through the Earth's core because it is a liquid. Therefore, the S-wave shadow zone covers the entire section of the Earth beyond 104°.