EARTHQUAKES
PowerPoint Presentation Outline Notes
What Is An Earthquake?
· A wave-like vibration
· Travels away from a point of sudden energy release
· Focus is the point of sudden energy release
· Epicenter is located at the earth’s surface immediately above the focus
What Causes Earthquakes?
· Most earthquakes are caused by faults
· Volcanoes
· Atomic explosions
Elastic Rebound Theory
· 1906 earthquake
· Strain built up along strike-slip fault
· Earthquakes - sudden release of energy
· Called elastic rebound theory
· Horizontal slippage
· Some faults are locked
Where Do Earthquakes Occur?
· Most earthquakes occur in linear belts
· 80% occur around the Pacific Ocean Basin
· Plate boundaries
Bay Area Faults
· San Andreas transform fault
· Two plates grind past each other
· Many branches off this fault system
o Hayward
o Rodgers Creek
o Calaveras
o Green Valley
Potential For Bay Area Earthquakes
· Are we overdue for an earthquake?
· 67-70% risk in 30 years
Which Parts Of The United States Are Vulnerable To Earthquakes?
· Southwest including California
· Pacific Northwest
· Yellowstone Area
How Are Seismic Waves Recorded?
· Seismographs record seismic waves
· Pen stays relatively still due to inertia of heavy mass
· Rotating drum moves with the ground vibration
Seismic Waves
Body waves move through the earth’s interior
· P (primary) waves move fastest
o Compressional
· S (shear) waves move more slowly
o Shake up and down
Seismograms Record Vibrations
· P Waves
· S Waves
· L or Surface Waves travel slowly
o Most dangerous
Seismograms Locate Epicenters
· Difference in arrival time between P and S waves can determine distance from epicenter
· Three or more stations are needed to determine the epicenter
How Are Earthquakes Measured?
· Richter scale measures the magnitude of energy released at the focus
o Open-ended scale - logarithmic increase
o Richter 3 to Richter 4 is 30 X
· Modified Mercalli scale measures the intensity of an earthquake according to damage observed
o Scale I-XII
What Determines the Amount of Damage in an Earthquake?
· Magnitude and duration of the earthquake
· Underlying geology
· Building construction
Effects of Earthquakes
· Ground Shaking
· Fault Rupture and Uplift
· Liquefaction
· Dam Breaks
· Landslides
· Tsunami
· Aftershocks
· Fire
Where is the Safest Place to Live?
Liquefaction
· Loose sand and mud turns into quicksand as groundwater rises
· Heavy objects sink in and light objects pop out
· Bayfill such as Emeryville and Alameda South Shore is vulnerable
What Causes a Tsunami?
· Movement of the ocean floor
Why Is a Tsunami Dangerous?
· A tsunami travels at over 800 kmh in open water
· Slows down and piles higher and higher in shallow water
· 30 meter high waves swamp the coast