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1. EARTHQUAKES

4. WHAT CAUSES THE
GROUND TO TREMBLE
LIKE THAT?

5. The Earth’s
surface is on
the MOVE.

6. EARTHQUAKES
An earthquake (also known as
a quake, tremor or temblor) is the perceptible
shaking of the surface of the Earth, which can be
violent enough to destroy major buildings and kill
thousands of people. - Wikipidea
An earthquake is a geological event inside
the Earth that generates strong vibrations.
An earthquake is what happens when two blocks
of the earth suddenly slip past one another.

8. 3 EARTHQUAKE CLUSTERS:
1.Foreshock
2.Mainshock
3.Aftershock

9. WHAT CAUSES
EARTHQUAKES?

10. WHAT CAUSES EARTHQUAKES?
Earthquakes can occur for a variety of reasons; however,
the most common source of earthquakes is movement
along a fault.
2. VOLCANIC ACTIVITY
1. NUCLEAR BOMBS
• exploding underground cause small local
earthquakes
• Earthquakes sometimes accompany volcanic
eruptions as huge masses of magma move
underground

12. WHAT CAUSES EARTHQUAKES?
 Earthquakes occur within the Earth’s crust
along faults that suddenly release large
amounts of energy that have built up over
long periods of time.
 The Earth’s crust near tectonic plate edges
are forced to bend, compress, and stretch
due to the internal forces within the earth,
causing earthquakes.

13. WHY DOES THE
EARTH SHAKE
WHEN THERE IS AN
EARTHQUAKE?

14. SEISMIC WAVES - are generated when rock
within the crust breaks, producing a tremendous
amount of energy. The energy released moves out in
all directions as waves.
1. BODY WAVES - spread outward from the focus in all
directions.
2. SURFACE WAVES - spread outward from the
epicenter to the Earth’s surface, similar to ripples on a
pond. These waves can move rock particles in a rolling
motion that very few structures can withstand. These
waves move slower than body waves.

15. BODY WAVES

16. PRIMARY (P) Waves SECONDARY (S) Waves
•Particle motion is parallel to
wave direction
•Travel fastest (arrive first)
•Travel through solid or fluid
•Particle motion is perpendicular
to wave direction
•Travel slightly slower
•Only travel through solid
Body Waves

17. SURFACE WAVES

18. LOVE Waves RAYLEIGH Waves
Surfaces Waves
• Side-to-side motion of the
ground surface. Can’t travel
through fluids.
• Ground moves in an elliptical path
opposite the direction of wave motion.
Extremely destructive to buildings.
Slowest type of seismic waves produced by earthquakes.

19. HOW ARE
EARTHQUAKES
RECORDED?

20. SEISMOGRAPHS - recording devices used to
produce a permanent record of the motion detected by
seismometers

21. MEASURING EARTHQUAKES
SEISMOMETERS
SEISMOGRAMS
- used to measure seismic waves
- permanent paper (or digital) records of the
earthquake vibrations
–Used to measure the earthquake strengths
SEISMOLOGIST
- scientist who studies earthquakes and seismic waves

22. HOW DO
SCIENTISTS
MEASURE THE SIZE
OF EARTHQUAKES?

23. MEASURING the “SIZE” EARTHQUAKES
INTENSITY
MAGNITUDE
• a measure of the effects an earthquake produces (on
both structures and people). Modified Mercalli scale
• a measure of the amount of energy released by an
earthquake. Richter scale

24. MERCALLI SCALE
I. Not felt except by a very few under especially favorable conditions.
II. Felt only by a few persons at rest, especially on upper floors of buildings. Delicately suspended objects
may swing.
III. Felt quite noticeably by persons indoors, especially on upper floors of buildings. Many people do not
recognize it as an earthquake. Standing motor cars may rock slightly. Vibration similar to the passing of a
truck. Duration estimated.
IV. Felt indoors by many, outdoors by few during the day. At night, some awakened. Dishes, windows, doors
disturbed; walls make cracking sound. Sensation like heavy truck striking building. Standing motor cars
rocked noticeably.
V. Felt by nearly everyone; many awakened. some dishes, windows broken. Unstable objects overturned.
Pendulum clocks may stop.
VI. Felt by all, many frightened. Some heavy furniture moved; a few instances of fallen plaster. Damage slight.
VII. Damage negligible in buildings of good design and construction; slight to moderate in well-built ordinary
structures; considerable damage in poorly built or badly designed structures; some chimneys broken.
VIII. Damage slight in specially designed structures; considerable damage in ordinary substantial buildings with
partial collapse. Damage great in poorly built structures. Fall of chimneys, factory stacks, columns,
monuments, walls. Heavy furniture overturned.
IX. Damage considerable in specially designed structures; well-designed frame structures thrown out of plumb.
Damage great in substantial buildings, with partial collapse. Buildings shifted off foundations.
X. Some well-built wooden structures destroyed; most masonry and frame structures destroyed with
foundations. Rail bent.
XI. Few, if any (masonry) structures remain standing. Bridges destroyed. Rails bent greatly.
XII. Damage total. Lines of sight and level are distorted. Objects thrown into the air.

25. Richter Magnitudes Description Earthquake Effects
Frequency of
Occurrence
Less than 2.0 Micro Micro-earthquakes, not felt. About 8,000 per day
2.0-2.9 Minor Generally not felt, but recorded. About 1,000 per day
3.0-3.9 Minor Often felt, but rarely causes damage. 49,000 per year (est.)
4.0-4.9 Light Noticeable shaking of indoor items, rattling noises. Significant damage unlikely. 6,200 per year (est.)
5.0-5.9 Moderate
Can cause major damage to poorly constructed buildings over small regions. At most
slight damage to well-designed buildings. 800 per year
6.0-6.9 Strong Can be destructive in areas up to about 100 miles across in populated areas. 120 per year
7.0-7.9 Major Can cause serious damage over larger areas. 18 per year
8.0-8.9 Great Can cause serious damage in areas several hundred miles across. 1 per year
9.0-9.9 Great Devastating in areas several thousand miles across. 1 per 20 years
10.0+ Great Never recorded; see below for equivalent seismic energy yield. Extremely rare (Unknown)
RICHTER SCALE

27. BEFORE AND
AFTER
EARTHQUAKES

28. BEFORE AFTER

29. BEFORE AFTER

30. BEFORE AFTER

31. BEFORE AFTER

32. CAN SCIENTISTS
PREDICT
EARTHQUAKES?

33. CAN SOME ANIMALS
OR PEOPLE TELL WHEN
AN EARTHQUAKE IS
ABOUT TO HIT?

34. CAN THE GROUND
CAN OPEN UP
DURING AN
EARTHQUAKE?

35. Earthquakes and Plate Tectonics
• Earthquakes are caused by plate inter-
actions along tectonic plate boundaries
• Plate boundaries are identified and
defined by earthquakes
• Earthquakes occur at each of the three
types of plate boundaries: divergent,
transform, and convergent
– At divergent boundaries, tensional forces
produce shallow-focus quakes on normal faults
– At transform boundaries, shear forces produce
shallow-focus quakes along strike-slip faults
– At convergent boundaries, compressional
forces produce shallow- to deep-focus quakes
along reverse faults