Rayleighaaltoja

Rayleighaaltoja, the Finnish term for Rayleigh waves, refer to a type of seismic surface wave that travels along the interface between two media, typically the Earth's crust and its underlying mantle. The waves were first described in 1885 by Lord Rayleigh, who demonstrated that such waves result from the combined effects of shear and compressional motion within a homogenous elastic medium.

These waves are characterized by elliptical particle motion at the surface, with both vertical and horizontal components. The horizontal motion is directed along the direction of wave propagation, while the vertical motion occurs in the same plane, creating a forward–backward loop in the particles. The speed of Rayleigh waves is typically lower than that of bulk P (compressional) and S (shear) waves, and depends on the elastic properties of the near-surface layers. Because of their surface confinement, Rayleigh waves are especially sensitive to the mechanical properties of shallow layers, and are thus commonly used in engineering seismology and subsurface imaging.

In the field of earthquake engineering, Rayleighaaltoja are a major contributor to ground motion that promotes damage to structures. Their amplified amplitudes in soft soils and coastlines are well-documented, and they play a crucial role in the design of seismic isolation systems. In medical ultrasound, which employs analogous Rayleigh-type vibrations, the principle of surface wave propagation enables high-resolution imaging of superficial tissues, thus enabling diagnostic applications such as elastography.

Overall, Rayleighaaltoja remain a foundational concept in both natural hazard assessment and applied physical sciences, bridging theoretical seismology and practical engineering applications.