P-wave is a kind of propulsive wave, which propagates at a speed of 5.5 ~ 7 km/s in the earth's crust and first reaches the epicenter, also known as P-wave, which makes the ground shake up and down, with weak destructiveness.
Shear waves are shear waves: the propagation speed in the earth's crust is 3.2 ~ 4.0 km/s, and the second kind reaches the epicenter, also called S waves, which makes the ground shake back and forth and left and right, which is more destructive.
Surface wave, also known as L wave, is a mixed wave excited when P wave and S wave meet on the surface. Its large wavelength and strong amplitude can only spread along the surface, which is the main factor causing strong damage to buildings.
The actual propagation speed of P-wave and S-wave depends on the density and inherent elasticity of rock. Granite: k is about 27× 10 10 dyne/cm2;
Water: k is about 2× 10 10 dyne /cm2.
μ is the shear modulus, indicating its stiffness.
Granite: μ is about1.6×1kloc-0/0 dyne/cm2;
Water: μ is 0.
Two kinds of elastic waves can propagate in an elastic solid with density ρ.
P wave, velocity vP =√(k+3/4μ)/ρ.
Granite: VP = 5.5 km/s;
Water: VP =1.5km/s.
S wave, velocity vS=√μ/ρ.
Granite: vs = 3.0km/s;
Water: vS=0 km/s.