Seismic Waves Flashcards
What is a characteristic of seismic waves?
Seismic waves are elastic
What are the two types of earthquake waves?
Body waves and surface waves
which waves are body waves?
P waves and S waves
What are the characteristics of P waves?
P waves are compressional waves
Travel at speeds of 6-8 km/s through the earth’s interior (travel through rock, solids liquids and gases).
Particle motion is parallel to direction of propagation.
Also called primary waves (thus the P).
Similar to sound waves
What are the characteristics of S waves?
S waves are shear waves
Travel at speeds of 3-5 km/s through the earth’s interior.
Particle motion is perpendicular to direction of propagation.
Also called secondary waves (thus the S).
Do not pass through liquids
What are surface waves?
Travel at speeds less than 3-4 km/s. They consist of dispersed wave trains
(different frequencies travel at different velocities) that travel around the earth at
its surface.
Love Waves
Particle motion is horizontal and perpendicular to the direction of propagation.
SH waves trapped in a low velocity surface layer by total internal refraction
Rayleigh waves
Particle motion is retrograde elliptical in direction of propagation
(like water waves, but retrograde elliptical particle motion)
Dispersion
Because seismic velocities increase with depth, longer wavelength surface waves travel faster than shorter wavelength waves. This property of the dependence of velocity on wavelength is known as “dispersion”
What are the two different types of S waves?
SH and SV
Total Internal Reflection
Requires ray path from a lower velocity to higher velocity medium It is the mechanism by which SH waves are trapped in the crust to form Love Waves
Reflection and refraction behavior when entering a different medium
A beam of light, when it reaches the boundary between two different media such as water and air, partly reflects and partly refracts. In (a) the refracted beam bends down as it enters the water.
NOTE: the ray will always bend toward the slower moving medium after initial refraction
Also: The faster the ray the larger the angle of refraction
Refraction behavior (same medium): slow to fast
A wave that enters a slower medium from a faster one bends away from the boundary (like light entering water from air)
refraction behavior: fast to slow
A wave that enters a faster medium from a slower one,
bends toward the boundary
Snells Law
sini/v1 = sinR/v2
Snell’s law is a formula used to describe the relationship between the angles of incidence and refraction, when referring to light or other waves passing through a boundary between two different isotropic media, such as water, glass and air
