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Earthquakes Chapter 19 Crustal Movement: Stress – The total force acting on crustal rocks per unit of area. 3 TYPES OF STRESS: Strain – The deformation of materials in response to stress. Strain (deformation) Elastic vs. Plastic Caused when a material is compressed, bent or stretched. Caused when a material is permanently deformed. Similar to stretching a rubber band by pulling on the ends. Similar to pulling a rubber band until it actually breaks. • The point at which Earth’s crust has reached its elastic limit is when permanent deformation occurs. Folds (elastic deformation) – There are 2 types of bends that can occurs in Earth’s crust. Syncline “sinks” Anticline folds up like a capital “A” Faults (plastic deformation) – breaks in the Earth’s crust along which Earth’s crust moves. Faults produce 2 sides (walls): Foot wall – The side of the fault which is thicker at the bottom (you can “walk” up it) Hanging wall – The side of the fault which is thicker at the top (you can “hang” from it) TYPES OF FAULTS Normal Fault – Tension pulls rock apart, forcing the footwall up and the hanging wall down. Normal Fault Animation Normal Fault Stress = Tension TYPES OF FAULTS Reverse Fault – Compression causes the hanging wall to move up and the footwall to move down. Reverse Fault Animation Reverse Fault Stress = Compression TYPES OF FAULTS Strike-Slip Fault – Shearing forces two parts of Earth’s crust past each other with NO vertical movement. Strike-Slip Animation Strike-Slip Fault Stress = Shearing Reverse, Normal, or Strike-Slip Fault? Normal Fault Tension Hanging Wall Sinks Down Reverse, Normal, or Strike-Slip Fault? Reverse Compression Hanging wall is pushed up Reverse, Normal, or Strike-Slip Fault? Strike-Slip Shearing No Vertical Movement Earthquakes – The vibration of Earth’s surface following a release of energy from Earth’s crust. Focus – The point Underground where an earthquake originates. Epicenter – The point on Earth’s surface directly above the focus. This is typically the location we about on the news. Inside Earthquakes Video Interior seismic waves – These waves travel through the inner layers of Earth. Primary Waves Secondary Waves -Travel twice as fast as S-Waves. -Travel half as fast as P-Waves. -Compressional Movement: rocks are squeezed and pushed in the same direction as the wave moves. -Rolling Movement: rocks shifted up and down perpendicular to the direction of the wave. -Move similar to a slinky that is stretched and then released. -Move similar to a rope that is being shaken up and down. COMPARE P WAVES AND S WAVES Shadow Zones – Areas on Earth where no seismic waves are recorded. -P waves can travel through all of the layers (solid, liquid and plastic), but they are deflected in different directions as they move from one layer to another. -S waves can travel through solid and plastic layers, but not liquid layers (the outer core). Shadow Zones Surface seismic waves – These are the slowest of the seismic waves and they only travel on Earth’s surface. Love waves cause a side to side movement of the surface. Raleigh waves cause an up and down movement of the surface. -When combined, these waves move the ground up and down and side to side simultaneously. -They cause the most damage because the create the most ground movement and take the longest time to pass an area. Locating the epicenter of an Earthquake: Triangulation Scientists use seismic data received from at least 3 stations to triangulate (the same process GPS uses) the epicenter of an earthquake. We will explore this process more in lab. 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 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. -The scale is from 0-10. Every whole number up on the scale represents an increase in energy of ten times more. MERCALLI SCALE Moment Magnitude Scale **This is the most accurate scale used today** -Introduced in 1979. -Measures earthquake strength based on the amount of energy released by calculating size of the fault, amount of movement, and type of rock (stiffness). -The moment magnitude scale is preferred over the Richter scale by seismologists because it is more accurate. -When hearing about an earthquake on the news, this is typically the final, most accurate magnitude given. 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 Earthquake Depth Shallow earthquakes cause the most damage. Intermediate earthquakes cause moderate damage Deep earthquakes cause the least damage. Earthquake Hazards: Structural Failure Earthquake Hazards: Land/Soil Failure Earthquake Hazards: Tsunamis A series of waves that occurs when the ocean is disturbed by earthquakes, underwater explosions or impacts. tsunami animation