Causes of Earthquakes

Types and Behavior of Seismic Waves• Body Waves

– Primary or Compressional– Secondary or Shear

• Surface Waves– Raleigh (large vertical displacements)– Love (shear)

Elastic Rebound Theory

3 m offset

Earthquake Focus and Hypocenter

Seismic Wave Types

Body Waves Surface Waves

Vp = k + 4/3µ

1/2

equations for velocities

density

µ shear modulus (rigidity)

k bulk modulus (rigidity)

Vs = µ

1/2

because shear modulus (rigidity) for fluid is zero,S waves cannot propagate through a fluid

consequence of equations is that P waves are 1.7x faster than S

can infer physical properties from P and S waves

Locating and Measuring Earthquakes

• Determining the Location of an Earthquake

• Measuring the Size of an Earthquake

• Location and Size of Earthquakes in the United States

Vertical Component Seismometer

Horizontal Component Seismomter

Distance - Time Relations

Earthquake Location by Range

Effects of Earthquakes

• Tsunamis• World Distribution of Earthquakes

• First-Motion Studies of Earthquakes

Modified Mercalli Intensity Index (1931)

1886 Charleston, SC earthquake

Pancaked Building - 1985 Mexico City

Earthquakes don’t kill people - buildings do!