1. Chapter 21 Section 2 Earthquakes & Volcanoespp

2. Earthquakes Occur due to plate movement faults
Introduction to Earthquakes
It’s an Earthquake Song

3. Earthquakes: Focus vs. Epicenter
Focus: point UNDER Earth’s surface where waves originate…along the fault line
Epicenter: point ON Earth’s surface directly above the focus…surface waves begin here and move outward
Focus of an Earthquake

4. Seismic Waves 3 types of seismic waves: P-waves S-waves Surface waves
Seismic Waves Song

5. P-Waves P (primary)-waves: move the fastest
Rocks are squeezed & pushed in direction of wave (longitudinal)
P-Wave Animation

6. S-Waves
S (secondary/shear)-waves: rocks move at right angles (transverse) to direction of waves
Slower than P-waves
S-Wave Animation

7. Surface waves Rocks move sideways and up & down
Slowest of the three types
of waves
Most destructive wave
Surface Wave Animation

8. How are earthquakes measured?
Seismograph: instrument that can detect, amplify, and record ground vibrations too small to be perceived by human beings
Seisomogram: a graph showing the motion of the ground versus time
Seismograph Animation
Seismograph-ing to the beat
Cali Seismogram Real Time

9. Travel-time curves
Measures the time between P & S-waves (that hit a particular seismic station)
Wave speed differs b/c of density & rigidity of Earth’s layers
Tells you the distance of location from epicenter
As the time between waves increases the distance from epicenter increases
Time & Distance= Direct relationship!

10. Locating the Epicenter
Use travel-time curve
Ex. Difference between P & S waves=6.3 min
What’s the distance from the epicenter?
4,000 km

11. Big Deal? What does that tell us…
By looking at travel-times of seismic waves to different stations, we can generate a probability of epicenter location (scale distance on map)
See circles around d1, d2 and d3?
Where all 3 circles intersect tells us epicenter!
Quake Movie Trailer

12. Determining Destruction
Richter Scale
measures magnitude (energy of largest seismic wave) on 1-10 scale
looking at the wave’s largest amplitude
Each magnitude is 10 times stronger than the previous magnitude
Ex: magnitude 8 earthquake releases as much energy as detonating 6 million tons of TNT!
Japan March 2011 Tsunami Photos Nat. Geo.
Tsunami Animation
Largest EQs Since 1900

13. Determining Destruction con’t
Modified Mercalli Scale
amount of shaking experienced at different locations (intensitydamage)
Varies based on:
overall magnitude
how far you are from the fault that ruptured in the earthquake
rock/ land texture or type (i.e. sand vs. concrete)
More meaningful measure of severity to the nonscientist because intensity refers to the effects actually experienced at that place.

14. Mt. St. Helens
Volcanoes

15. Zones of Volcanism
Volcanism: all the processes associated with the release of magma, hot fluids, and gas
Fueled by magma
Rises to surface because less dense
Called lava once at surface

16. Location of Volcanoes Mostly determined by plate boundaries
NOT RANDOM!
Mostly determined by plate boundaries
Most at convergent and divergent boundaries
5% far from boundaries

17. Major Belt of Convergent Volcanoes
Circum-Pacific Belt (Pacific Ring of Fire)
Outlines the Pacific Plate
Convergent volcanism:
Plates colliding
Continental subduction zones
Characterized by explosive eruptions

18. Divergent Volcanism Formed where plates move apart
New ocean floor is produced here
Pillow lava forms at ocean ridges
Characterized by non-explosive eruptions
About 2/3 of Earth’s volcanoes occur at divergent boundaries
Ex: Icelandic volcanoes uncharacteristically explosive due to hot spot

19. Bend in chain change in direction of plate movement!
Hot Spots
Unusually hot regions of Earth’s mantle where high-temperature plumes (columns) of magma rise to the surface
Usually form far from plate boundaries
Stationary – plate moves over spot
Ex: Hawaiian Islands
Bend in chain change in direction of plate movement!

20. Volcano Anatomy
Conduit: tube-like structure that magma travels through to surface
Vent: opening that lava comes out of
Crater: bowl-shaped depression around the vent
Usually less than 1 km (0.6 mi)
in diameter

21. Types of Volcanoes 3 types: Appearance determined by:
Type of material that forms volcano
Type of eruptions
3 types:
Shield
Cinder cone
Composite 1. 2. 3.

22. Shield Volcanoes Broad, gently sloping sides
Non-explosive, quiet eruptions
Made of layers of basaltic lava
Largest type (width wise)
Ex: Mauna Loa (Hawaii)

23. Cinder Cone Steep sides, cone shaped Mostly basaltic lava
Explosive eruptions
Smallest type (most less than 500 m or 0.3 mi high)
Often on or near larger volcanoes
Ex: Lassen Volcanic Park (California)

24. Composite Volcano Large, cone shaped, concave slopes
Much larger than cinder cones
Made of layers of rock (harden lava) from explosion and lava flows
Violent eruptions (with periods of quiet ones)
Ex: Mt, Augustine (Alaska), Mt. St. Helens (Washington)

25. Mt. Vesuvius, Italy
Catastrophic eruption of A.D. 79 destroyed the cities of Pompeii and Herculaneum and killed at least 16,000 people
Buried 10’ deep with lava & ash
Thermal energy570 degrees F (300 degrees C)
most died instantly of extreme heat, with many casualties shocked into a sort of instant rigor mortis.
Most died instantly of extreme heat, with many casualties shocked into a sort of instant rigor mortis.