In elastodynamics, Love waves are essentially horizontally polarized shear waves (SH waves) guided by an elastic layer, which is "welded" to an elastic half space on one side and borders vacuum on the other side. In seismology, Love waves (also named Q waves) are surface seismic waves that cause horizontal shifting of the earth during an earthquake. A.E.H. Love predicted the existence of Love waves mathematically in 1911; the name comes from him (Chapter 11 from Love's book "Some problems of geodynamics", first published in 1911). They form a distinct class, different from other types of seismic waves, such as P-waves and S-waves (both body waves), or Rayleigh waves (another type of surface wave). Love waves travel with a slower velocity than P- or S- waves, but faster than Rayleigh waves.