Stresses, Faults, Folds, and
Earthquakes
Types of Stresses on Layers of Rocks:
Types of FoldsAnticline- an upward fold in the rock
Syncline- a downward fold in the rock
Syncline
Anticline
Syncline “sinks”
Anticline folds up like a capital “A”
Syncline
Anticline
4 Types of FaultsFault- A break in the Earth’s surface where
movement occurs.
Hanging Wall and Footwall
Hanging Wall (HW)- The piece of rock that is wider at the top, where your head would be located in the elevator.
Footwall (FW)- The piece of rock that is wider at the bottom, where your feet would be located in the elevator.***You can “walk” up the footwall
Normal and Strike-Slip Faults• Normal Fault- Tension
pulls rock apart and the HW moves down and the FW moves upward.
• Strike-Slip Fault- Shearing pushes and pulls two rocks layers past each other without any upward or downward motion.
NORMAL FAULTS
STRIKE-SLIP FAULTS
Reverse and Thrust Faults• Reverse Fault-
Compression forces the HW upward and the FW downward.
• Thrust Fault- compression creates a reverse fault in which the HW slides at a very low angle over the FW.
COMPRESSION FAULTS
Strike-slip Fault
Stress= Shearing
Reverse Fault
Stress = Compression
Normal FaultStress = Tension
PRACTICE IDENTIFYING
FAULTS
Reverse, Normal, or Strike-Slip Fault?
Normal Fault
Tension
Hanging Wall Sinks Down
Reverse, Normal, or Strike-Slip Fault?
Strike-Slip Fault Shearing Horizontal Movement of Layers
Reverse, Normal, or Strike-Slip Fault?
Reverse Compression Hanging wall is pushed up
JAPAN QUAKE’S FAULT LINEThe earthquake occurred along this convergent plate boundary where subduction happens (convergent boundary).
What type of stress/fault is occuring here?
Tsunami FormationElastic Rebound
Earthquakes
EARTHQUAKES
Focus and EpicenterFault- A break in the earth’s crust where movement occurs.
Focus- the origin of an earthquake underground.
Epicenter- the point on the earth’s surface directly above the focus of an earthquake.
Earthquake Waves• Primary Wave- waves that move through
Earth by causing particles in rocks to move back and forth in the same direction. (compressionial waves)– Primary wave move twice a fast
as secondary.– Primary waves can travel through
liquid or plastic materials as well as solids- but the speed changes as it travels through solids.
• Secondary Waves- wave that move through the earth by causing particles in rocks to move a right angles to the direction of the wave. ( up and down motion)– Secondary waves can travel through
plastic or solid materials but NOT liquid. COMPARE P WAVES AND S WAVES
Interior of the Earth and Seismic Waves• P Waves can travel
through both solids and liquids
• S waves can travel through solids but not liquids.
• Based on the speed, direction and angles of the waves, we can determine the consistency of the interior of the Earth!
• Shadow zone- areas on Earth (opposite to origin of quake) where no P or S waves are felt.Shadow Zones
Surface Earthquake Waves
A. Raleigh Waves-The R waves move continuously forward, although the individual particles move vertically in an elliptical path
B.Love Waves- The L waves also travel forward, but the individual particles move back and forth horizontally.
Surface waves usually follow the P and S wave, traveling along the land surface like water waves. There are several types of surface waves; the two most important are Raleigh waves (R) and Love waves (L) , named for the scientists who first identified them.
How do we measure earthquakes?
Richter Scale Mercalli Scale-Created by Charles Richter in 1934.-This scale measures earthquakes based on the largest seismic wave recorded during a quake.
-The scale is from 0-10. Every whole number up on the scale represents an increase in energy of ten times more.
**The original (less used today) scales**
-The original scale used to measure quakes. Created in 1902 by Giuseppe Mercalli.
-Considered less accurate, because it uses eyewitness observations of damage to estimate the intensity of the quake.
MERCALLI SCALE
**This is the most used scale today**
Moment Magnitude Scale
-Introduced in 1979 in order to be more accurate than the Richter and Mercalli Scales, because its based on physical features of the quake instead of recordings using instruments.
-Measures earthquake strength based on the amount of energy released. This amount is calculated by analyzing the physics of the earthquake.
-The moment magnitude scale is preferred over the Richter scale by seismologists because it is more accurate.
-In simple terms, this scale multiplies the area of the fault surface and the distance the Earth moves along the fault to calculate the magnitude.
Earthquake Richter Scale Moment Magnitude
New Madrid, MO, 1812 8.7 8.1
San Francisco, CA 1906 8.3 7.7
Prince William, AK 1964 8.4 9.2
Northridge, CA,1994 6.4 6.7
Famous Earthquakes1) Anchorage, Alaska - March 27, 1964
-This is the most powerful U.S. earthquake in recorded history.-It registered as a 9.2 on the Richter scale. -The rumbling lasted nearly 5 minutes. -Ground fissures, collapsing buildings, and an ensuing tsunami killed over 130 people.
2) San Francisco, California – 1906-Significant earthquake in that it was one of the first instances where scientists were able to record information on seismic waves.-Caused approximately $400,000,000 of damage (at the time)-Several eye-witness accounts refer to the movement of the roads to be similar to the undulation of waves in the ocean.-Fires raged on for days, and S.F. had to be rebuilt.
Famous Earthquakes
3) Indian Ocean – December 26, 2004-9.2/9.3 magnitude earthquake, making it one of the most powerful ever recorded on Earth.-The infamous tsunami that ensued killed over 200,000 people.-Released an amount of energy 1502 times more powerful than the Hiroshima atomic bomb.
4) Chile – May 22, 1960-The most powerful earthquake ever officially recorded at a magnitude of 9.5.-The damage is estimated to be at over 3 billion dollars, and nearly 6,000 killed.
-Once the red slab that is “stuck” finally gives way, this is when the earthquake occurs. The recoil of the plate causes the energy to be released.
TSUNAMI
A series of waves that occurs when the ocean is disturbed by earthquakes, underwater explosions or impacts.12/26/04- Southeast Asia experienced a large scale earthquake along the Ring of Fire that created a series of tsunamis that killed 225,000 people and displaced over 1.2 million people! The tsunami slammed into the coasts of several nations within two hours after the quake.
tsunami animation
