Longitudinal wave.

Seismic waves are divided into three types according to their propagation modes: longitudinal waves, transverse waves and surface waves. Longitudinal waves are propulsive waves with a propagation speed of 5.5 to 7 kilometers/second in the earth's crust. They are the first to arrive at the epicenter. They are also called P waves. They cause the ground to vibrate up and down and are less destructive.

Transverse waves are shear waves: they propagate in the earth’s crust at a speed of 3.2 to 4.0 kilometers/second, and are the second to reach the epicenter. They are also called S waves. They cause the ground to shake back and forth, left and right, and are destructive. Stronger. Surface waves, also known as L waves, are mixed waves excited by longitudinal waves and transverse waves when they meet on the surface. Its wavelength is long and its amplitude is strong, and it can only propagate along the ground surface. It is the main factor causing strong damage to buildings.

Extended information

When an earthquake source releases energy, the earth's primary vibration continues without force. At this time, its vibration frequency only depends on elasticity. The nature of the earth itself.

The exact basic principles of mathematical simulation are still similar to the analysis of plucked string instruments. The Greeks realized more than 2,000 years ago that the harmonics of music depend only on the length, density and tightness of the strings. This free vibration is called eigenvibration. Likewise, the intrinsic vibrations within the dialed Earth depend on the size and density of its geological formations and the elastic modulus of the entire interior.

An elastic sphere has only two different types of intrinsic vibrations. One type, called T-shaped or toroidal oscillations, involves only horizontal movement of the Earth's rocks; the particles of the rock reciprocate on a spherical surface - the Earth's surface or some internal interface. The second type is called S-shaped or spherical oscillation. The motion components of spherical oscillation are both along the radius and in the horizontal direction.

Baidu Encyclopedia-Seismic Waves