# Earthquakes Flashcards

What is an earthquake?

A release of elastic energy stored in the lithosphere, built up from gradual deformations.

Where do earthquakes normally happen?

Near fault lines.

What are earthquakes at faults parameterised by?

The slip vector, the slip angle and the area of the fault plane.

What is the focus?

Point from which slip begins and from which the slip propagates.

What is epicentre?

Closest point on the Earth’s surface to the focus point.

What are 3 things we can observe from an earthquake?

- Damage afterwards
- Movement along fault
- Seismic waves

What are the 4 types of fault?

- Thrust fault (compression)
- Normal fault (expansion)
- Strike-slip (horizontal movement)
- Oblique fault

What is the modified mercalli scale?

Qualitative scale indicating damage to buildings and infrastructure.

What is the equation or the seismic moment M0?

M0 = μ*A*|u| [Nm]

What is the magnitude scale?

Logarithmic scale to show size of the earthquake.

What is the equation for the magnitude Mi?

Mi = (log(base 10) of E) + corrections, where E is some measurement such as the seismic moment etc

What do we need to estimate the energy of the earthquake?

Measurement of the seismic waves and the location of the focus.

How would you get the energy if you had the equation of a wave displacement, A = A(max)*cos(kx-ωt)?

- KE 1/2
*m*v^2

- So = 1/2 * ρ*(dA/dt)^2

What is the equation for the surface wave magnitude, M(s)? What are the letters?

M(s) = log(base 10) of (A(max)/T)+1.66*log(base 10) of Δ + 3.3

Δ = angular distance in degrees from epicentre A = magnitude T = seismic wave period

What is the equation for body wave magnitude M(B)? What are the letters?

M(B) = log(base 10) of (A(max)/T) + Q(D,h), where Q is the correction term as a function of distance D from the epicentre, h the depth of focus