S-wave
Introduction
S-waves, also known as shear waves, are a type of elastic wave that move along the Earth's interior during an earthquake. Unlike P-waves, which are compressional and move in the direction of the wave propagation, S-waves move perpendicular to the wave direction and are responsible for the shaking felt during an earthquake.
Characteristics
S-waves are slower than P-waves, with a typical velocity of 3.5 km/s in the Earth's crust. They are transverse waves, meaning they vibrate perpendicular to the direction of wave propagation. This results in a shearing or twisting motion, which can cause significant damage during an earthquake.
S-waves can only travel through solid materials and are blocked by liquids and gases. This property is used in seismology to determine the structure of the Earth's interior. The absence of S-waves in certain areas of the Earth's interior indicates the presence of liquid or gas.
Propagation
The propagation of S-waves is governed by the elastic properties of the medium. The speed of an S-wave depends on the shear modulus and density of the medium. In general, S-waves travel slower in less rigid materials and faster in more rigid materials.
S-waves can be polarized, meaning they can vibrate in more than one direction. The direction of polarization can provide information about the source of the earthquake and the structure of the Earth's interior.
Detection and Measurement
S-waves are detected and measured using seismometers. The arrival of S-waves at a seismometer station is used to determine the distance to the earthquake epicenter. By comparing the arrival times of P-waves and S-waves at different seismometer stations, seismologists can triangulate the location of the earthquake.
Role in Earthquake Damage
The shaking associated with S-waves can cause significant damage during an earthquake. The shearing motion can cause buildings and other structures to collapse, and can trigger landslides in hilly or mountainous areas.
Use in Seismology
In seismology, S-waves are used to probe the structure of the Earth's interior. The way S-waves reflect and refract at interfaces within the Earth provides information about the composition and state of the material. The absence of S-waves beneath the Earth's outer core suggests that it is liquid.