Transcript Name of School Date Earthquakes and Seismology Plate Tectonics A Century of Earthquakes: 1906-2006

Name of School
Date
Earthquakes and Seismology
Plate Tectonics
A Century of Earthquakes:
1906-2006
Global Seismographic
Network
2006 Earthquakes > M5.5 in the world
2006 Earthquakes > M5.5
How Many?
Earthquake Magnitude and Equivalent Energy Comparisons
Source: http://www.iris.edu/edu/onepagers/no3.pdf
Earthquakes
generate Seismic
Waves that travel
around the globe
and tell us about
the Earth’s
interior.
Simple Seismometer
A simple way to
measure shaking
from earthquakes.
To see it in action, watch this 14 sec video
http://www.youtube.com/watch?v=DX5VXG
mdnAg&NR=1
What is an Earthquake?
Earthquake: The sudden release of
elastic energy by fracture over some area
of the earth.
What is an Earthquake?
Earthquake: The sudden release of
elastic energy by fracture over some area
of the earth.
Earthquake: The sudden slip on a fault
(release of elastic energy), and the
resulting ground shaking and radiated
seismic energy caused by the slip.
Fault: A fracture (crack) in the earth, where
the two sides move past each other and the
relative motion is parallel to the fracture.
Typical Plate Boundaries
Plate
Boundaries
& earthquakes
Types of Faults
A fence built over a fault…
1906 San Francisco
Earthquake
Fence Offset
Offset Stream Channels in Central California
Types of Seismic Waves



P-wave:
 Primary Wave. Compressional wave, like a
Slinky© being pushed and pulled.
S-wave:
 Secondary Wave. This is a shear wave where
particles move perpendicular to the travel direction
of the wave.
Surface Waves:
 Both Love and Rayleigh Waves. Only shallow
particles are disturbed. Love waves are sideways,
Rayleigh are vertical (like ocean waves).
Types of
Seismic
Waves
Types of Seismic Waves
Seismographs
Horizontal
Vertical
Distance to quake epicenter
Fig 3.22
Note:
P-wave first
S-wave second
Surface waves last
S
P
Time lag between p and swave arrival is called Dt.
L
Maximum Amplitude = 540 mm
Tp=14s
Ts=23s
Locating Earthquakes
Fig. 3.23
Locating Earthquakes
Locating Earthquakes
Earthquake Size
Richter Magnitude:
Relative Size of an Earthquake
(based on seismograph shaking)
Seismic Moment/Moment Magnitude:
Absolute Size of an Earthquake
(based on energy released)
Modified Mercalli Intensity:
How much I’m shakin’
(based on talking to people)
Calculating Richter Magnitude
A.K.A Local Magnitude
ML = log10A - log10Ao
A is the amplitude of the s-wave measured at given station
Ao is the amplitude of a MR=0 event at the same distance
P
S
Log of the Amplitude for a Magnitude 0 Earthquake
M=4
M=0
Earthquake: The sudden slip on a fault (release of
elastic energy), and the resulting ground shaking and
radiated seismic energy caused by the slip.
Aki’s Seismic
Moment Formula
Mo =  s A
Where:

is the shear
modulus.
S is the average
slip on the faulted
area.
A is the area of
the fault plane
over which slip
has occurred.
Shear modulus () can just be thought of as the
strength of the faulted material
Modified Mercalli Intensity
Based on response of humans and structures
I (not felt except by few)
XII (total destruction)
Still useful for comparison with older earthquakes
for which there were no instrument records
http://earthquakes.usgs.gov/
Earthquake Info on the Internet
http://earthquakes.usgs.gov/eqcenter/dyfi.php
Earthquake Info on the Internet
Did You Feel It???
Go online and tell us!
http://www.data.scec.org/recenteqs.html
Earthquake Info on the Internet
Southern
California with
Faults &
the Big Bend
Southern California from Space(1)
Southern California from Space
With a Few Major Faults
(1900-1950)
(1850-1900)
Historical
Earthquakes
(1000-1800)
Historical
Earthquakes
(1950-2004)
(1800-1850)
Smith and Sandwell, 2006
Thank You for Your Attention

Questions?