• What do you call the remanent magnetism from ancient rocks recording the direction and strength of the Earth’s magnetic field at that time?
Recap
What are Earthquakes?
• The shaking or trembling caused by the sudden release of energy
• (also known as a quake, tremor or temblor)
• Usually associated with faulting or breaking of rocks
• Continuing adjustment of position results in aftershocks
Where Do Earthquakes Occur and How Often?
~80% of all earthquakes occur in the circum-Pacific belt– most of these result from convergent margin
activity– ~15% occur in the Mediterranean-Asiatic belt– remaining 5% occur in the interiors of plates
and on spreading ridge centers– more than 150,000 quakes strong enough to
be felt are recorded each year
Causes of Earthquakes• Passing the Elastic Limit Causes Faulting
– Applied stresses can cause rocks to bend and stretch
– Eventually rocks will break away from one another• Area in which the rocks break and
move is called a fault• Vibrations produced is called an
earthquake– Earth’s crust movement causes the
stresses applied
What is the Elastic Rebound Theory?
• Explains how energy is stored in rocks–Rocks bend until the strength of
the rock is exceeded–Rupture occurs and the rocks
quickly rebound to an undeformed shape
–Energy is released in waves that radiate outward from the fault
The Focus and Epicenter of an Earthquake
• The point within Earth where faulting begins is the focus, or hypocenter
• The point directly above the focus on the surface is the epicenter
Measuring Earthquakes
• Seismology– Seismologists - People who study earthquakes and
seismic waves– Use instruments called seismographs
• Record seismic waves• A drum with a sheet of paper vibrates and a
stationary pen marks the vibrations on the paper• The height of the lines are used to measure the
energy released from the earthquake called the magnitude
What are Seismic Waves?
• Response of material to the arrival of energy fronts released by rupture
• Two types:– Body waves
• P and S
– Surface waves• R and L
Body Waves: P and S waves
• Body waves– P or primary waves
• fastest waves• travel through solids,
liquids, or gases• compressional wave,
material movement is in the same direction as wave movement
– S or secondary waves• slower than P waves• travel through solids
only• shear waves - move
material perpendicular to wave movement
Surface Waves: R and L waves
• Surface Waves– Travel just below or along the ground’s surface– Slower than body waves; rolling and side-to-side
movement– Especially damaging to buildings
The Economics and Societal Impacts of EQs
Damage in Oakland, CA, 1989• Building collapse
• Fire• Tsunami• Ground failure
How are the Size and Strength of an Earthquake Measured?
• Intensity– subjective
measure of the kind of damage done and people’s reactions to it
– isoseismal lines identify areas of equal intensity
How are the Size and Strength of an Earthquake Measured?
• Magnitude– Richter
scale measures total amount of energy released by an earthquake; independent of intensity
What are the Destructive Effects of Earthquakes?
• Ground Shaking– amplitude, duration, and damage increases in poorly
consolidated rocks
Tsunamis
• Caused by the movement of the ocean floor– Causes a disruption in the water– Some are so wide that a large ship can travel
over the wave without knowing– Recent earthquake in the Indian Ocean created
a tsunamis that was 100 feet high and moving at 500 mph
Can Earthquakes be Predicted?
Earthquake Precursors – changes in elevation or tilting of land surface,
fluctuations in groundwater levels, magnetic field, electrical resistance of the ground
– seismic dilatancy model– seismic gaps
Can Earthquakes be Predicted?Earthquake Prediction Programs
– include laboratory and field studies of rocks before, during, and after earthquakes
– monitor activity along major faults– produce risk assessments
Can Earthquakes be Controlled?
• Graph showing the relationship between the amount of waste injected into wells per month and the average number of Denver earthquakes per month
• Some have suggested that pumping fluids into seismic gaps will cause small earthquakes while preventing large ones
Family Readiness•Create a family Earthquake plan
•Know the safe spot in each room
•Know the danger spots
•Decide where your family will reunite if separated
•Keep a list of emergency phone numbers
•Develop a survival kit for work, car, and home
Home Preparedness•Learn how to shut off gas, water, and electricity
•Check chimneys, roofs, and wall foundations for stability
•Secure heavy furnishings
•Secure water heater and appliances
•Keep heavy objects on lower shelves
•Maintain emergency food, water, medicine, first aid kit, tools, and clothing
Emergency Supplies•First Aid supplies Band-Aids antibiotic ointment latex gloves cold/hot packs ace bandages arm sling Tylenol or Advil diarrhea medication•Equipment work gloves shovel tents sleeping bags ready to eat foods clothing radio, flashlights CASH
Emergency Food•Camp or backpacking stove propane tank•Canned foods manual can opener•Granola bars•Energy bars
Safe Drinking Water•Store a supply of water 1 and 5 gallon containers do not store on concrete•Purifying tap water 8 drops bleach per gal of water add bleach when storing or, boil for 10 minutes•Water from water heater turn off gas or electric turn off cold water supply once cooled, drain at bottom•Other sources toilet storage tank melted ice cubes water trapped in pipes
During an Earthquake•Stay away from windows, bookcases, file cabinets, heavy mirrors, and other heavy objects that could fall
•Duck under a desk or sturdy table
•Watch for falling plaster or ceiling tiles
•Stay undercover until the shaking stops, and hold onto your cover
•If the desk or table you are under moves… move with it
•If in your car, stop, but not on a bridge, or under trees or a power line
•If outside, stay outside, and move to an area clear of overhead trees, power lines, or objects that could fall from a structure
•Don’t forget about aftershocks
After The Earthquake•Be prepared for aftershocks, plan for cover when they occur
•Check for injuries, give first aid as necessary
•Remain calm, try to reassure others
•Wear shoes to avoid injury from broken glass
•Check for fire and take appropriate actions
•Check gas, water, and electric lines
•Tune to emergency broadcast system on radio