1. Honors Earthquakes Chp. 8
Earthquake: vibration of Earth produced by rapid release of energy, usually along a break in Earth’s crust

2. Focus: where earthquake originates (deep in Earth)
Epicenter: point directly above focus on Earths surface

3. Fault: fracture along which movement occurs, in the lithosphere
3 types of faults:
Normal Fault: horizontal tension, hanging wall drops down foot wall (foot wall become higher point)
Reverse fault: (Thrust): horizontal compression, hanging wall pushed up over foot wall (foot wall becomes lower point)
Strike-slip fault: horizontal shear
Foot
wall
Hanging wall
Foot
wall
Hanging wall

4. Cause of Earthquakes Stress & Strain
Stress: force per unit area causes fractures
Strain: deformation of material due to stress

5. Lead to:
Elastic deformation:
material will return to normal if stress is decreased
Elastic limit: point between elastic & ductile deformation
Ductile Deformation: permanent deformation due to stress & strain, occurs after elastic limit is exceeded
Failure: breakage, Earthquake

6. Elastic Rebound Hypothesis:

7. Aftershock: smaller earthquakes (could be hundreds) that follow a major earthquake, hinder rescue efforts
Foreshock: small earthquakes that happen before a major earthquake

8. Measuring Earthquakes
Seismographs: sensitive instrument measures vibration
Seismogram: (seismos = shake, gramma = what is written) written record produced by seismometer of all 3 waves

9. Seismic Waves
1. Surface waves (L-waves, complex waves): Rock moves up & down and side to side; side to side motion most destructive, most destructive wave overall, slowest moving wave (90% slower than S waves)

10. 2. Primary waves (P-waves, longitudinal): squeezes & pulls rock in direction of traveling wave, fastest wave (1.7 X faster than S waves)
3. Secondary waves (S-waves, transverse): rocks move at right angle in relation to wave direction

11. Time-Travel Graph What is it used for?
S-wave: travel slower than P-waves
P-waves: Travel faster than S-waves
What is it used for?

12. Locating an Earthquake
1. Determine P and S wave arrival time to seismographs
2. Calculate the difference between P & S wave arrival times
3. Determine epicentral distance
4. Minimum of three stations needed to determine epicenter

13. Seismic Belts
Areas of greatest seismic activity, narrow & follow plate boundaries
80% in Circum-Pacific Belt
15% in Mediterranean-Asian Belt

14. Measuring Earthquakes
Intensity: amount of earthquake shaking at a given location (not quantitative)
Magnitude: amount of energy released from source of earthquake (quantitative)

15. Richter scale 1935 Charles Richter
Cal Tech (California Institute of Technology)
Only useful for small shallow earthquakes within 500 km of epicenter
Used mostly by news reporters

16. Richter scale: based on amplitude of largest seismic wave generated, use logarithmic scale
Wave size increases by a factor of 10
Magnitude 6 wave size is 10X lager than magnitude 5, and 100X larger than a magnitude 4
Energy released increased by a factor of 32X
Magnitude 6 energy is 32X greater than magnitude 5, and 1024X greater than a magnitude 4

17. Moment magnitude scale: used by most scientists, derived from amount of displacement
Calculated using:
seismograph data size
average movement along fault
Area of surface breakage
Strength of rock
See table 1 page 227 in book

18. Modified Mercalli scale: measures intensity on I to XII scale, XII greatest damage earthquakes can cause
The same earthquake can have different Mercalli scale ratings (depends on distance from epicenter) Why?

19. Depth & Focus related to earthquake magnitude
Deeper the focus smaller the vibrations
Crust
darker
area
Lithosphere
Hole thing

20. Destruction from Earthquakes
Depends on:
Intensity (why intensity & not magnitude?)
Duration of vibration (material, magnitude)
Nature of material under structure or area
Liquefaction: loosely compacted earth & saturated sediments
Liquefies during an earthquake causing settling

21. Design of structure
Unreinforced masonry (brick) buildings most at threat
Wood and steel have more flexibility
Generally why is wood better than steel?

22. Tsunamis: waves created by rapid displacement of water, with long wavelength off shore and short wavelength near shore (travel very fast off shore, slow near shore)
Tsunami warning systems are common in the Pacific Ocean & were not put in the Indian Ocean until after the 2002 Sumatra Tsunami
Amplitude
increases
in shallow
Water only

23. Tsunamis are created by:
Earthquakes activity
volcanic activity
Landslides
Asteroids or meteor impacts

24. High ground is the safety zone during a tsunami
Tsunami damage is caused by huge surge that pushes inland long distances due to waves long wavelength
High ground is the safety zone during a tsunami
Before
After

27. Other dangers resulting from earthquakes:
Landslides
Ground subsidence
Fires

28. Predicting Earthquakes:
Shore-range predictions: monitor & measure; uplift, subsidence, strain in rock, water level, pressure in wells, radon gas emissions & electromagnetic properties in rock. Have not been successful
Long-range predictions: forecasts occurrence within 30 to 100+ years by studying historic records & seismic gaps, based on the idea earthquakes are cyclical, help in determination of building codes; Are predictions accurate? What is a seismic gap?

29. Earth’s Layers Defined by Composition
Crust: thin rock outermost layer
Oceanic: 7 km, basalt & gabbro (density 3 g/cm3)
Continental: 8-75km (average 40km), granitic (grandiorite), less dense than oceanic (density 2.7 g/cm3)

30. Mantle: 82% of Earth’s volume, dominant rock type peridotite, extends to depth of 2890 km, density 3.4 g/cm3
Core: center sphere composed of iron-nickel greatest concentrations of metal), extreme pressure density 13 g/cm3

31. Earth’s Layers Defined by Physical Properties
Lithosphere: outer most layer crust and upper mantle, cool ridged shell, 100 km in thickness
Asthenosphere: small amount of melting due to temp & pressure, weak layer because near melting point
Upper mantle: lower lithosphere & asthenosphere

32. Lower mantle: more ridged layer, rocks very hot capable of gradual flow
Outer Core: liquid layer, flow generates Earth’s magnetic field, 2260 km thick
Inner Core: solid due to pressure, 1220 km thick

33. Discovering Earth's layers
Mohorovicic’s evidence of 1909: velocity of seismic waves increased abruptly below 50km (the Moho)
Moho: boundary between crust and mantle
More evidence:
P waves can travel through a liquid (but they lose velocity)
S waves can not travel through liquid

34. P wave: due to refraction in core, 105 degrees to 140 degrees
Shadow zones:
P wave: due to refraction in core, 105 degrees to 140 degrees
S wave: due to outer core (cannot travel through liquid), waves stop at 105 degree mark
Asthenosphere
Higher viscosity
103 degrees
Outer core
low viscosity
Outer core
Lower viscosity
Inner core
solid

35. Discovering Earth’s Composition Drilling (direct observation)
Seismic data
P & S wave shadow zones
Nuclear test
1960 allowed for measurement of inner core

36. Kola Peninsula Deepest Well Cool Facts:
Began to drill in 1970
5 years to drill 7000 m (1975)
9 years to drill the next 5000 m! (1984)
Stuck at 12,000 m in 1989
Reached 12,262 m in 1994
At the bottom of the well…
Rocks 2.9 billion years old
Temperature 190°C ~ 2X the temp of boiling water

37. Local Faults: