Crust Deformation • Deformation is the bending, tilting, and breaking of the earth’s crust. • Plate tectonics is the major cause of crustal deformation. • Stress is a force that causes pressure in the rocks of the crust. • Strain – a change in the shape or volume of rocks that results from the stress of being squeezed, twisted, or pulled apart.
Stress • Compression – reduces the volume of rocks. This occurs when they are squeezed together. • Tension – pulls rocks apart and makes them thinner. • Shearing – pushes rocks in opposite horizontal directions. Sheared rocks bend, twist, or break apart as they slide past each other.
Folds • Folding – this occurs when rock responds to stress by becoming permanently deformed without breaking. • Folds appear as a wavelike structures in rock layers.
Faults • There are two types of breaks in rocks: • Fracture: when there is no movement in the rocks along either side of a break. • Fault: when the rocks move after breaking.
Earthquakes • Vibrations of the earth’s crust are called earthquakes. • Earthquakes usually occur when rocks under stress suddenly shift along a fault. • Normally the rocks along both sides of a fault are pressed together tightly. • Friction prevents the rocks from moving past each other – the fault is “locked.” • When the stress becomes too great, the rocks suddenly grind past each other. • This slippage causes the trembling and vibrations of an earthquake.
Elastic Rebound Theory • Elastic Rebound Theory states that rocks on each side of a fault are moving slowly, and when the rocks are stressed to a certain point, they will fracture, separate at their weakest point, and spring back to their original shape, or rebound. • Aftershocks are the smaller tremors that can be felt after an earthquake. • Focus – the area along a fault where the slippage first occurs • Epicenter – the point on the earth’s surface directly above the focus
Seismic Waves • When an earthquake occurs, seismic waves radiate outward in all directions from the focus. • Earthquakes that cause the most damage usually have a shallow focus. This means that they are not very deep under the ground – within 43.5 miles from the earth’s surface.
Earthquake Zones • The earth has three major earthquake zones. • Pacific Ring of Fire • Mid-ocean Ridge • Eurasian-Melanesian Mountain Belt • Most earthquakes occur along or near the edges of the earth’s lithospheric plates. • It is at these moving plate boundaries that stress is greatest and rocks experience the greatest amount of strain.
Recording Earthquakes • Seismograph – this is the instrument that can detect and record seismic waves. • Every earthquake produces three major types of seismic waves that each travel at different speeds and causes different movements in the earth’s crust.
Waves • P waves – primary waves – they move the fastest and are the first to be recorded. Travel through solids and liquids • S waves – secondary waves – they are the second to be recorded. Only travel through solid material. • L waves – slowest moving and last to be recorded. These cause the surface to rise and fall and create the most damage.
Richter Scale • This is used to express the magnitude of an earthquake. • Magnitude is a measure of the energy released by an earthquake. • Each increase of one whole number of magnitude represents a release of 31.7 times more energy than that of an earthquake measuring one whole number lower. • An 8 would be 31.7x31.7 (~1000) times more than a 6
Tsunamis • A major earthquake with an epicenter on the ocean floor sometimes causes a giant ocean wave called a tsunami. • These are caused by faulting and underwater landslides. • Faulting may cause a sudden drop or rise in the ocean floor. • The water above a landslide is thrown into an up-and-down motion, thereby creating a series of tsunamis.
Possible Damage from Earthquakes • Death/injury • Collapsed buildings • Landslides • Fires • Explosions • Flood • Flying glass • Falling objects
Earthquake Safety • Before an earthquake, be prepared! • Canned food, bottled water, flashlights, batteries, portable radio, have a plan • During an earthquake, stay calm! • Inside – protect yourself from falling debris, stay away from windows, doors, and things that can fall over • Do not run outside. • In a car – stay in the car until the tremors stop and stop in a place away from tall buildings, tunnels, power lines, and bridges. • After an earthquake, be cautious! • Check for fire hazards, wear closed-toe shoes, avoid power lines.
Your Task: • Create a creative, eye-catching, colorful, informative, comprehensive brochure and include the following: • How earthquakes happen • What causes them? • Explain how the fault lines and plate boundaries play a role in earthquakes. • Include a section on plate tectonics • How tsunamis happen • What causes them? • Possible damage that can result from an earthquake • Earthquake safety • What to do before an earthquake. • What to do during an earthquake. • What to do after an earthquake.