"We learn geology the morning after an earthquake."
~ Ralph Waldo Emerson
~ Seismology ~
Earthquakes in History
Earthquakes / More Quakes
Recent Equakes / Latest Equakes
The Science of Earthquakes / Fun Facts
What Causes Earthquakes: An Interactive World Map
Animations of Plate Boundaries / Annenburg Interactive Plate Boundaries
~ The Three Types of Stress ~
Types of stress that cause rock to fold and fracture:
Tension & Compression & Shearing
~ Folding ~
Folding is due to the slow force of compression acting upon rock.
Over millions of years, solid rock can slowly
bend, stretch, break, tilt, fold, and slide.
Anticline (upward arch) and Syncline (downward arch):
Faulting and Folding
Over 90% of EARTHQUAKES occur at PLATE BOUNDARIES.
What about the other 10%? (Answer: Faults)
~ The Three Types of Plate Boundaries ~
A. Divergent ( moves apart / separates / extensional )
B. Convergent ( moves together / collides / compressional )
C. Transform ( moves in opposite directions, horizontally / sliding )
Below: Map Showing the Three Types of Tectonic Plate Boundaries
Convergent (compressional) & Divergent (extensional) & Transform (sliding)
Below: Map of U.S. Earthquake Hazard Zones
~ Earthquake Faults ~
Fault: A crack in the crust along which movement occurs.
Hanging Wall: The Rock Block ABOVE the Fault
Foot Wall: The Rock Block BELOW the Fault
Earthquake Fault Animations
Test your knowledge:
Identify the Hanging Wall and Foot Wall.
What kind of faults are shown above and below?
Transform (Lateral) Fault
( Stress: Shearing )
( Stress: Tension )
Reverse (Thrust) Fault
( Stress: Compression )
Left: Normal Fault ..............................Right: Reverse Fault
~ Focus and Epicenter ~
Focus and Epicenter
FOCUS: Underground location along a fault where displacement (movement) occurs.
EPICENTER: Point on the surface directly above the focus (greatest shaking occurs here).
TRIANGULATION: Locating the Epicenter
~ Seismic Waves ~
Primary Waves: arrive first / travel the fastest / can go through both solids and liquids / are gentle
Secondary Waves: arrive second / travel through solids (not liquids) / cause much damage
Surface Waves: travel the slowest / make the ground roll like ocean waves / are the most destructive
P-waves compress and expand like an accordian or like slinky coils that are held and then released.
S-waves travel up and down & side to side like a rope that is flicked.
Left: P-waves / Right: S-waves
Click here: Green Dot Demo / P and S Blue Dot Animations
Primary (P) Secondary (S) Surface (L/R)
Below: Surface Waves (Love Waves and Rayleigh Waves)
Below: Surface Wave Damage to an Athletic Track (Japan)
How do scientists rate the severity of an Earthquake?
Click here: The Richter, Mercalli, and Moment Magnitude Seismic Scales
~ Earthquakes of New England ~
Our New England Earthquakes / Equake Map / History
Mass Earthquake Resource Guide / The Weston Earthquake Observatory
The Clinton-Newbury Fault
The Lake Char-Bloody Bluff Fault
Above: Exposed Fault at the Bloody Bluff, Concord, MA
Above: Earthquake Proof Home on Virginia Road in Concord, MA
Earthquake-Proof Geodesic Dome Homes in California
"You fish on your side; we fish on our side; nobody fishes in the middle"
Click here: The Lake Char Sing-along Song / Ethel Mermon / Let's Go Canoeing
The 1755 Cape Ann, Massachusetts Earthquake
on the Lake Char-Bloody Bluff Fault
Cape Ann Earthquake of 1755 / More Info / Verses
Richter Magnitude Estimate: 6.5 - 7.0
~ Earthquake Safety ~
Earthquake Safety Regulations / Damage Photos
Disaster Plan / Hazards
Drop, Cover, Hold On Song: Caribbean Style
Earthquake Rumble Song / Earthquake Safety Turtle Song
DROP, COVER and HOLD during an earthquake!
Rather than: PANIC, CRY and DIE!
What to Do After the Quake
Above: Rescue Dog
Post-Earthquake Danger: Bridge/Bridge/Bridge / Freeway / Building Collapse / Photos
Post-Earthquake Danger: Seismic Sea Wave-Tsunami (See Below)
Post-Earthquake Danger: Gas Pipe Breakage and Fire
Post-Earthquake Danger: (Fore) & Aftershocks
Post-Earthquake Danger: Liquefaction
Earthquake-Proof Your Home / Easy Steps / Build / Prepare
Above: Epic Fail
~ Liquifaction ~
Mexico City, Mexico, 1985
Above: Damage to structural foundations due to Liquefaction
Liquifaction (Quicksand Soil) = Water-Saturated Loose Sediment that Flows like a Liquid.
Mini "Sand Blow Craters" form as a result of Liquefaction:
Water from the "saturated zone" perculates up to the surface:
Above: Aquifer and Water Table
Above: Note the tighter packing of sediment grains after an earthquake
(Less pore space = Less room for groundwater)
Learn About Liquefaction / Video Clips
Above: Liquefaction Zone after the Sendai, Japan earthquake of 2011
~ Tsunami ~
Click here: Tsunami Information Page