S-wave

An S-wave is a seismic shear wave that moves material perpendicular to its direction of travel. It travels through solids, not liquids, and typically arrives after the P-wave.

Shear wave: A wave in which particles oscillate perpendicular to the direction the wave travels. S-waves are the seismic form of this broader wave type.
S–P time method: An earthquake-location method that estimates distance from the difference between S-wave and P-wave arrival times. The delay between these arrivals provides the method’s distance estimate.
Elasticity: The property of a material that allows it to return to its original shape after deformation. Elastic restoring forces let solids transmit shear disturbances.
SKS phase: A seismic phase that travels as an S-wave in the mantle, converts to a P-wave in the outer core, then returns as an S-wave. Its path through the core makes it useful for studying mantle anisotropy.
Shear modulus: A measure of a material’s resistance to deformation by shear stress. It determines whether a material can support S-waves and helps set their speed.
Seismic shadow zone: A region on Earth’s surface where seismic waves from an earthquake are not directly detected. The absence of direct S-waves on the far side of Earth indicates a liquid outer core.
Elastic wave: A disturbance that propagates through a material by its elastic deformation. S-waves belong to this broad family of waves.
ScS phase: A seismic phase that travels as an S-wave through the mantle, reflects from the core–mantle boundary, and returns through the mantle. Its reflection samples the boundary between the solid mantle and liquid outer core.
P-wave: A compressional seismic wave that typically travels faster than an S-wave and can pass through solids, liquids, and gases. Its faster arrival and compressional motion distinguish it from S-waves.
Earth's outer core: Earth’s liquid layer of iron-rich metal between the mantle and inner core. Its liquid state cannot support the shear motion of S-waves.

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