# Seismology Flashcards

What is seismology?

The study of seismic waves passing through the Earth (body wave) or along its surface (surface wave).

What is the Laplacian version of the wave equation?

d^2u/dt^2 = c^2 * ∇^2u

What is a general solution to the wave equation?

Plane waves: u(r,t) = u0*exp(i(kr-ωt))

What is the bulk modulus?

The ratio of hydrostatic pressure increase to resulting relative decrease in volume: K = -dP/(dV/V) [Pa]

What is the shear modulus?

Distorts the material without changing the volume (amount of distortion per unit stress: μ = (F/A)/(Δ

x/l) [Pa]

How does the bulk modulus compare to the shear modulus in normal materials?

K > μ > 0

What is the wave equation for compressional waves?

d^2Ф/dt^2 = α^2*∇^2Ф, where α = sqrt((K+4μ/3)/ρ)

What is the wave equation for shear waves?

d^2Ψ/dt^2 = β^2*∇^2Ψ, where β = sqrt(μ/ρ)

What can compressional waves travel in? What can shear waves travel in?

Compressional - solids and liquids

Shear - solids only

What can measuring the propagation speeds α and β give us?

Can tell us about properties of deeply buried layers and earthquake location (focus).

What is a compressional and shear wave?

Compressional is a longitudinal wave whereas shear is a transverse wave

What are the two main types of surface waves?

- Rayleigh waves: no transverse particle motion

- Love wave: only transverse motion

What is the epicentre and focus of an earthquake?

The focus is the centre of the earthquake. The epicentre is the position on the earths surface vertically above the focus.

How is energy distributed in a wave?

Equally distributed across wavefront.

What is the equation for energy of a 2D wave (surface wave)?

E ∝ 1/2πr