Download Earthquakes

Earthquakes
Chapter 19
What is an earthquake?
• Natural vibration of the ground
• Caused by movement along fractures or
volcanic eruptions
Most earthquakes occur when…
• Rocks fracture or break deep within the Earth.
• Fractures form when STRESS, the forces per
unit area acting on a material, exceeds the
strength of the rocks involved.
3 Kinds of stress
1. Compression:
Pushes together
1. Tension: Pulls
apart
1. Shear: Twists
Faults
• Many rocks that make up the crust fail when
stress is applied to quickly.
• The result is a system of fractures called
FAULTS.
Three Types of Faults
Seismic Waves
• Vibrations of the ground during an earthquake
are called Seismic Waves (there are 3 types).
1. Primary Waves (P Waves)
• Squeeze and pull rocks in the same
direction along the wave direction.
• The first wave to arrive at an
earthquake
http://daphne.meccahosting.com/~a0000e89/insideearth2.htm
Secondary Waves (S Waves)
• Cause rocks to move at right angles in
relation to the direction of the wave.
http://daphne.meccahosting.com/~a0000e89/insideearth2.htm
Surface Waves
• Move in 2 directions as they pass through
rock.
• Produces motion in the upper crust
– Motion can be up and down
– Motion can be around
– Motion can be back and forth
• Travel more slowly than S and P waves
• More destructive
Focus –
point inside the Earth where an
earthquake begins
Epicenter – point on Earth’s surface above
focus
Seismology: the study of
earthquakes
How Seismographs (seismometers)
Work
the pendulum remains
fixed as the ground
moves beneath it
Typical Seismogram
http://isu.indstate.edu/jspeer/Earth&Sky/EarthCh11.ppt
How do scientists calculate how far a location is
from the epicenter of an earthquake?
• Scientists calculate the difference
between arrival times of the P waves
and S waves
• The further away an earthquake is, the
greater the time between the arrival of
the P waves and the S waves
How are Earthquakes Measured?
Richter Scale: The size of the largest
seismic wave in magnitude.
How are Earthquakes Measured?
Mercalli Intensity Scale
Most earthquakes…. Are
associated with tectonic plate
boundaries.
Almost 80% of all earthquakes
occur in the Circum-Pacific Belt!
Destruction to buildings
Pancaking”
“
• Where
structural
buildings fall
and debris
resembles a
stack of
pancakes.
Tsunamis
http://www.uwgb.edu/dutchs/EarthSC-102VisualsIndex.HTM
Formation of a tsunami
http://isu.indstate.edu/jspeer/Earth&Sky/EarthCh11.ppt
Tsunami Warning System
http://isu.indstate.edu/jspeer/Earth&Sky/EarthCh11.ppt