Seismic wave

When recorded by a seismic observatory, their different travel times help scientists locate the quake's hypocenter.

In geophysics, the refraction or reflection of seismic waves is used for research into Earth's internal structure.

Body waves travel through the interior of the Earth along paths controlled by the material properties in terms of density and modulus (stiffness).

S waves can travel only through solids, as fluids (liquids and gases) do not support shear stresses.

Surface waves from very large earthquakes can have globally observable amplitude of several centimeters.

The existence of these waves was predicted by John William Strutt, Lord Rayleigh, in 1885.

In a layered medium (e.g., the crust and upper mantle) the velocity of the Rayleigh waves depends on their frequency and wavelength.

[9] They are named after Augustus Edward Hough Love, a British mathematician who created a mathematical model of the waves in 1911.

These waves can also be generated along the walls of a fluid-filled borehole, being an important source of coherent noise in vertical seismic profiles (VSP) and making up the low frequency component of the source in sonic logging.

[3] Of the fundamental toroidal modes, 0T1 represents changes in Earth's rotation rate; although this occurs, it is much too slow to be useful in seismology.

The mode 0T2 describes a twisting of the northern and southern hemispheres relative to each other; it has a period of about 44 minutes.

The naming of seismic waves is usually based on the wave type and its path; due to the theoretically infinite possibilities of travel paths and the different areas of application, a wide variety of nomenclatures have emerged historically, the standardization of which – for example in the IASPEI Standard Seismic Phase List – is still an ongoing process.

[14] The path that a wave takes between the focus and the observation point is often drawn as a ray diagram.

[14][15] For example: In the case of local or nearby earthquakes, the difference in the arrival times of the P and S waves can be used to determine the distance to the event.

In the case of earthquakes that have occurred at global distances, three or more geographically diverse observing stations (using a common clock) recording P wave arrivals permits the computation of a unique time and location on the planet for the event.

In practice, P arrivals from many stations are used and the errors cancel out, so the computed epicenter is likely to be quite accurate, on the order of 10–50 km or so around the world.

P wave and S wave from seismograph
Velocity of seismic waves in Earth versus depth. [ 1 ] The negligible S -wave velocity in the outer core occurs because it is liquid, while in the solid inner core the S -wave velocity is non-zero
Body waves and surface waves
Patterns of seismic wave travel through Earth's mantle and core. S waves can not travel through the liquid outer core, so they leave a shadow on Earth's far side. P waves do travel through the core, but P wave refraction bends seismic waves away from P wave shadow zones.
The sense of motion for toroidal 0 T 1 oscillation for two moments of time.
The scheme of motion for spheroidal 0 S 2 oscillation. Dashed lines give nodal (zero) lines. Arrows give the sense of motion.
Earthquake wave paths
The hypocenter/epicenter of an earthquake is calculated by using the seismic data of that earthquake from at least three different locations. The hypocenter/epicenter is found at the intersection of three circles centered on three observation stations, here shown in Japan, Australia and the United States. The radius of each circle is calculated from the difference in the arrival times of P and S waves at the corresponding station.
P and S waves separating with time