chapter 12: earthquakes. where do earthquakes tend to occur? earthquakes can occur anywhere, but...
TRANSCRIPT
Where do earthquakes tend to occur?
Earthquakes can occur anywhere, but they tend to occur on and near tectonic
plate boundaries.
San Andreas Fault, California
What is a fault?
A fault is a break or crack in Earth’s crust along which rocks shift their position.
What is seismology?
Seismology: a science that deals with earthquakes and with artificially produced vibrations of Earth
• Seismograph: an instrument that records vibrations in the ground.
• Seismogram: a tracing of earthquake motion that is recorded by a seismograph.
~300 miles long!
• shaking lasted ~1 minute
• felt from southern Oregon to central Nevada, and south of Los Angeles (maybe in SD?)
1906 San Francisco Earthquake M 7.7 to M7.9?
1906 San Francisco Earthquake M 7.7 to M7.9?
Massive fires followed the earthquake and burned for several days
• Magnitude: a measure of its strength of an earthquake.
• Intensity: (in Earth Science) the amount of damage caused by an earthquake.
1906 San Francisco Earthquake M 7.7 to M7.9?
Casualties and Damage
Casualties 3000+
People left homeless 225,000
Buildings destroyed 28,000
At the plate boundary
Elastic Rebound: the sudden return of elastically deformed rock to its undeformed shape
Aftershocks…
• Aftershocks are smaller earthquakes that occur after a larger earthquake
– Happen near the mainshock– Are smaller magnitudes than the mainshock
Seismograph: The instrumentApparatus to measure and record vibrations
Seismogram: The actual wiggleRecord of an earthquake recorded by a seismograph
The difference between a “Seismograph” and a “Seismogram”
FuturePast
Seismic Waves• Body Waves: in geology, a seismic wave that
travels through the body of a medium.
• Surface Wave: in geology, a seismic wave that travels along the surface of a medium and that has a stronger effect near the surface of the medium that it has in the interior.
P-waves• primary wave• compression wave• fastest of the seismic
waves• can travel through solids,
liquids, and gases
Surface waves• 2 types: Love waves and
Rayleigh waves• Slowest seismic waves• May cause the greatest
damage in an earthquake
S-waves• secondary wave• shear wave• second-fastest seismic wave• can only travel through
solids
Seismic wavesSeismic waves
Surface Waves• Love Waves: cause rock
to move side to side and perpendicular to the direction in which the waves are traveling.
• Rayleigh Waves: cause the ground to move with an elliptical, rolling motion.
Travel time from San Diego to Los Angeles
P-waves 25 seconds 25 seconds
S-waves 41 seconds 41 seconds
Surface waves 50 seconds50 seconds
Seismic Waves and Earth’s Interior• Shadow Zone: an area on
Earth’s surface where no direct seismic waves from a particular earthquake can be detected.
• Shadow zones exist because the materials that make up Earth’s interior are not uniform in rigidity.