1. Earthquakes
Chapter 6

2. 6A Tectonic Forces What is an EarthQuake? Tectonic Forces
How do we measure?
Tectonic Forces
Stress
Compression
Tension
** Shear
Boundaries
Divergent
Convergent-collision or subduction, great compression and shear forces
Transform-ocean, basins, mid-ocean ridges, sea floor spreading, shear forces present
Strain- ductility, joints, fault, brittle, elasticity
Rocky materials show strain, store potential energy under stress, when broken, energy is released suddenly
Weak, brittle rocks fracture easily, not much stored energy
Soft, ductile rocks, change shape
Elastic rocks or strong but brittle, break releasing lots of energy

3. 6B Faults & Joints Joints Faults No visible movement
Vary in size & appearance
Single or groups
Form at angle to stress
Form in various ways
rock breaks and forms joints, very weak seimic waves b/c no motion at joint
Faults
Tectonic activity (movement) forms faults
Fault plane, strike, dip
Face of a fault is never flat, never straight, strike and dip changes along its length

4. Faults resistance to movement depends on how slippery the fault is
Classifying Faults
Dip-slip fault
Normal
Reverse
Thrust fault
Strike-slip fault
Transform fault
Most quakes we feel happen at less than 45 mi below the earth’s surface
Faults resistance to movement depends on how slippery the fault is
Lubricants for a fault may include oils, water, certain minerals
Locked faults build up shear stress
Secondary quakes after an initial quake are aftershocks

5. Earthquake Videos

6. 6C Earth Waves & Seismology
Seismometers
Special instrument that detects earthquake waves and is attached to a way to record or graph the changes in the waves
Found at seismic stations
Seismographic recording is a seismogram
Seismic waves have amplitude and frequency
Types of Waves
Body Waves – pass right through the earth
P Waves
Primus- relatively small amplitudes and short wavelengths
Travel through both solid and liquid rock
S Waves
Secundus- larger amplitudes, stronger and slower
Travel through the earth
Surface Waves
Travel along the earth’s surface, move about same speed as S waves, far more destructive
Two wave forms – Rayleigh and Love

7. 6C Earth Waves & Seismology
Locating Earthquakes
Focus- center of an earthquake’s activity
Epicenter- the spot on the earth’s surface above the focus
The closer the focus the more the ground shakes at the epicenter
3 Seismic Stations are needed to locate the epicenter of an earthquake
By studying the arrival times of the P, S and Surface waves, scientists can determine the depth of the focus
Most quakes happen in faults along tectonic plate boundaries

8. 6D Effects of Earthquakes
Richter Scale used to report the strength of an earthquake
Named for seismologist Charles Richter, 1935
Given in units of magnitude- indicates the energy released by the earth movement
Difference between magnitudes is 31.6 times as much energy
Doesn’t work well for earthquakes over a 7 magnitude
Doesn’t work well for earthquakes detected farther than 435 mi away
Public most familiar with this scale
Moment Magnitude scale
Can measure stronger more distant earthquakes
Earthquake Intensity
How much damage actually results from an earthquake
Magnitude, depth of focus, distance of epicenter, kinds of soil and rock formations, duration
Modified Mercalli Intensity scale (MMI)
Earthquake destructiveness scale

9. 6D Effects of Earthquakes
Earthquake Hazards
Building collapse
Fire
Tsunamis
Landslides
Earthquake Prediction
We cannot predict earthquakes
We can’t recognize the signs of an earthquale about to happen
Seismic gap- an area along a fault where an earthquake hasn’t occurred
By continuing to study earthquakes and make progress we are exercising wise dominion over the earth through science