1. Faults & Earthquakes
These can be either constructive or destructive forces 3 basic types of geologic forces 1. Tension: pulling force ← → 2. Compression: pushing force → ← 3. Shearing: forces sliding past each other in opposite directions. ↑↓

2. Fault: a fracture in earth’s crust where movement occurs
3 types of Faults:
1. Normal (tension) fault:
one side drops in relation
to the other.
2. Reverse (compression)
fault: one side pushes up
in relation to the other.
3. Strike-Slip (shear): fault:
horizontal shift in opposite
directions.

3. PLATE TECTONIC STRESSES
Plate boundaries and faults (= cracks where plate sections are moving in different directions) cause friction as plates move
Plates in a fault zone have STICK-SLIP motion
Periods of no movement (stick) and fast movement (slip)
Energy stored as plates stick,
Energy released as plates slip

4. EARTHQUAKES sudden movement or shaking of the Earth
Caused by plate tectonic stresses
Located at plate boundaries & faults within plates
Resulting in breakage of the Earth’s brittle crust
(2 ½ minute earthquake video)

5. SEISMIC WAVES produced by the release of energy
move out in circles from the point of rupture (focus)
Types of waves: surface & body (travel inside & through earth’s layers)
- P waves: longitudinal – compression (back and forth movement of rock) arrives 1st; travels thru solid, liquid, gas
S waves: sideways (transverse – shear) movement of rock; travel thru solids only; arrives 2nd.
L waves (surface): when both P & S waves reach the surface

6. EARTHQUAKE WAVES Seismographs record earthquake waves
Seismograms show: Amplitude of waves
(how much rock moves or vibrates)
- Distance to the epicenter -
Earthquake direction
How to read a Seismograph:
- P & S (body waves) move
through earth & arrive first.
P & S waves used to calculate magnitude of
earthquake.
- Amplitude = height of wave (how much the rock moves; size of vibration)
Surface waves move along surface – not felt opposite side of earth

7. EARTHQUAKE WAVES
FOCUS = place deep within the Earth and along the fault where rupture occurs
EPICENTER = geographic point on surface directly above focus
The epicenter is determined by taking
seismic readings from at least 3 stations
are taken and circles drawn from
those stations based on time
intervals from those stations.
The point where all circles
intersect is the epicenter.
This also referred to as
Triangulation.
(locating the epicenter vide o (3 1/2 minutes)

8. EARTHQUAKE MAGNITUDE
measures the size of seismic waves  the energy released by the earthquake
Richter scale=measurement of energy released based upon wave amplitude (size of vibration)
<2 to ~10
Amplitude of wave goes up by 10 (Logarithmic scale)
What you need:
Amplitude (size of vibration = wave height)
Time between arrival of 1st P and 1st S waves

9. Mercalli Scale: Measures the intensity of an earthquake based on qualitative data (damage to man-made structures)
MERCALLI VS. RICHTER

10. ISOSEISMIC MAPS show the distribution of intensities
Loma Prieta Earthquake 1989
Connects areas of with the same Modified Mercalli number
Areas are colored according to Modified Mercalli number

11. EARTHQUAKE DAMAGE Most caused by SURFACE waves (arrive last)
Landslides
Building damage
Liquefaction

12. LIQUEFACTION
The process that occurs during earthquakes when loose soil particles (sand and soil, not bedrock) turn into a watery, slurry mix as a result of the seismic vibrations.
Results in a loss of soil strength & the ability of the soil to support weight
(liquifaction video 2 ¼ minutes)
(liquifaction video 2: 1 ½ minutes)

13. Most volcanoes and earthquakes occur in the ring of fire, an area
circling the Pacific Ocean.
New Madrid fault is an area
of active earthquake activity
in the American mid-west.
A Tsunami is a giant tidal
wave often caused by an
underwater earthquake.
(Tsunami video 2 ¾ minutes)