Earthquakes Photo credit USGS Causes of Earthquakes Types

Earthquakes Photo credit: USGS

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 1906 San Francisco Earthquake

Elastic Rebound Animation

Offset Lettuce Rows - El Centro, CA

Earthquake Focus and Hypocenter

Earthquake Focus Animation

Seismic Wave Types Body Waves Surface Waves

equations for velocities Vp = Vs = k + 4/3µ r 1/2 r density µ shear modulus (rigidity) k bulk modulus (rigidity) because shear modulus (rigidity) for fluid is zero, S waves cannot propagate through a fluid consequence of equations is that P waves are 1. 7 x faster than S can infer physical properties from P and S waves

Wave Animations

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

Seismograph Animation

First Arrivals - Seismographic Records

Distance - Time Relations

P vs. S Wave Travel Time Curves

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!