Transcript Powerpoint

Where are we?
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19.
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17.
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Intro to geology
Plate tectonics
Minerals
Rocks
Igneous rocks
Volcanism
Weathering & erosion
Sediments and Sedimentary rocks
Metamorphic rocks
Rock record and Geologic time
Rock deformation
Earthquakes
Evolution of continents
Exploring Earth’s Interior
Earth beneath the ocean, shorelines
Mass wasting
Hydrologic cycle and Groundwater
Streams
Deserts & winds
Glaciers, Ice Ages
Landscapes
Energy and Mineral Resources
Earth’s environment, Global Change,
Human Impacts
Dynamic
motions
External
factors
Resources
CHAPTER 19
Earthquakes
1) Some recent Earthquakes
2) What is an Earthquake
3) Seismology
4) Locating an Earthquake
5) Earthquake intensity and magnitude
6) Earthquake and plate tectonics
7) Earthquake destruction
Earthquakes : Study questions
Know the definition of an earthquake and how it is related
to fault movement
Foreshocks, aftershocks, elastic rebound
What is the difference between earthquake focus and
epicenter?
Know the three different kinds of seismic waves, and their
characteristic motion, and properties of propagation.
How is an earthquake epicenter located?
Earthquake depth and how they are related to different
kinds of plate boundaries and increasing distance from a
subduction zone.
Know the Richter magnitude scale and what each unit
means with respect to increase in wave amplitude and
energy.
Which factors contribute to the destruction caused by
earthquakes?
2) What is an earthquake?
Fault - crack in Earth where slip occurs
Earthquake – vibration of earth, often caused by slippage along a fault
Earthquake focus - fault slip location
Epicenter – point on earth’s surface directly above focus
From: Tarbuck/Lutgens: Earth
Remember from Ch. 11: Rock deformation
Fault definition: a fracture where displacement has occurred:
rocks on either side of fault have moved relative to each other.
2) What is an earthquake?
elastic rebound
- plates are continually moving & fault is stuck
- crust starts deforming (stores elastic energy)
- fault breaks, releases elastic energy, rock “snaps back”
Fig. 19.12
fault
2) What is an earthquake?
aftershocks
small earthquakes
that follow an initial
earthquake in same
vicinity
foreshocks
small earthquakes
that sometimes
precede a large one
by few days
See Fig. 19.3
3) Seismology
seismology
- the study of earthquake “waves”, earthquakes, Earth
seismic waves
ancient
Chinese
seismograph
instrument to
record seismic
waves
seismogram - recording of ground shaking from seismographs
3) Seismology
“body waves”
Types of seismic waves
travel in Earth’s interior
P-waves (“P” for primary)
Expansion/compression:
push/pull motion
S-waves (“S” for secondary)
Shear:
side-to-side motion
“surface waves”
travel on Earth’s surface
Figure Story 19.5
3) Seismology
Types of seismic waves
Motion produced by the
different wave types
P-wave
S-wave
Surface-wave
4) Locating an earthquake
P-waves & S-wave travel at different speeds
fastest
Recipe:
1. Measure time between P and S wave on seismogram
2. Use travel-time graph to get distance to epicenter
3. Draw circle on a map with radius of that distance
4. Three or more circles should intersect at EQ!
4) Locating an earthquake
See Fig. 9.16
1. Measure time between P and S wave on seismogram
2. Use travel-time graph to get distance to epicenter
3. Draw circle on a map with radius of that distance
4. Three or more circles should intersect at EQ!
5) Earthquake Intensity and magnitude
 Richter Magnitude
Richter magnitude - concept introduced by Charles
Richter in 1935
Amplitude of the largest seismic wave recorded (P, S,
or surface) and distance
Note: Logarithmic scale
 Moment Magnitude
 Related to physical properties of faulting
Proportional to seismic energy released
Proportional to area of fault break
Fig. 19.7
5) Earthquake Intensity and magnitude
 Large Earthquakes occur less frequently than smaller ones!
Fig. 19.8
5) Earthquake Intensity and magnitude
6) Earthquake and plate tectonics
 recall: fault types (from Ch. 11)
See Fig. 19.10
6) Earthquake and plate tectonics
Shallow: Normal faulting, transform faulting, thrust (=reverse) fault
Intermediate+ Deep: subduction zones
See Fig. 19.13 and 19.12
7) Earthquake destruction
 important factors:
Intensity & duration of shaking
Soil type (soft? hard rock?)
Building design
 other effects:
Liquifaction
Tsunamis
7) Earthquake destruction
 important factors:
Intensity & duration of shaking
Soil type (soft? hard rock?)
Building design
 other effects:
Liquifaction
Tsunamis
Seismic hazard map
(see Fig. 19.21)
7) Earthquake destruction
 important factors:
Intensity & duration of shaking
Soil type (soft? hard rock?)
Building design
 other effects:
Liquifaction
Tsunamis
Fig. 19.18
Earthquakes :
A few sample MC
What does the elastic rebound theory describe?
A.
B.
C.
D.
the build-up and release of stress during an earthquake
the fluctuations in groundwater prior to an earthquake
the formation of mountain ranges by successive earthquakes
the uplift of the crust in response to erosion
Earthquakes :
A few sample MC
What causes the up-and-down wiggles on the seismogram?
A.
B.
C.
D.
electromagnetic pulses
ground vibrations
tsunami waves
variations in air pressure
Earthquakes :
A few sample MC
Which of the following correctly lists the order in which seismic waves arrive at a
seismograph station?
A.
B.
C.
D.
P waves  surface waves  S waves
P waves  S waves  surface waves
S waves  P waves  surface waves
surface waves  P waves  S waves
Earthquakes :
A few sample MC
An earthquake’s Richter magnitude is based on ______.
A.
B.
C.
D.
the amount of energy released during an earthquake
the amount of ground movement caused by seismic waves
the distance between the earthquake and the seismograph station
the observed effects on people and structures
Earthquakes :
A few sample MC
The ground motion during a Richter magnitude 8 earthquake is ______ times greater
than the ground motion during a Richter magnitude 6 earthquake.
A. 2
B. 10
C. 100
D. 1000
Earthquakes :
A few sample MC
How many seismograph stations are needed to locate the epicenter of an earthquake?
A. 1
B. 2
C. 3
D. 4
Earthquakes :
A few sample MC
Shallow earthquakes, less than 20 km deep, are associated with ___________.
A.
B.
C.
D.
convergent plate boundaries
divergent plate boundaries
transform plate boundaries
all of the above