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Earthquakes Faults & Stress Write everything in BLUE! What are Earthquakes? • The shaking or trembling caused by the sudden release of energy beneath Earth’s surface. • Usually associated with faulting or breaking of rocks • Continuing adjustment of position results in what is known as aftershocks What is stress? The force that acts on rock to change its shape 3 Types of stress Shearing Tension Compression Shearing: stress that pushes rock in opposite directions. Causes masses of rock to slip past each other. Tension • Stress that stretches rock so it becomes thin in the middle. – Causes valleys Compression • Stress that squeezes rock until it folds or breaks. • Causes hills Questions • What is the relationship between compression and a convergent boundary? Questions • What is the relationship between compression and a convergent boundary? – Both compression and convergent boundary squeezes rocks together to form mountains or hills. How is energy stored in Rocks? – Rocks are put under stress so they become deformed or bend. – Once the strength of the rock is exceeded rupture occurs and the rocks quickly rebound to an undeformed shape – Energy is released in waves that radiate outward from the fault A break in the Earth’s crust is called a Fault • 3 types of faults Strike-Slip Fault • There is little up or down motion • A strike-slip fault that forms the boundary between two plates is called a transform boundary. • Shearing stress causes strike-slip faults Strike-Slip Fault Example Normal Fault • The hanging wall slips downward below the footwall. • The Normal Fault that forms the boundary between two plates is called a divergent boundary. Normal Fault Example: Rio Grande Rift Valley Reverse Fault • The hanging wall slides up and over the footwall. • The reverse fault that forms the boundary between two plates is called a convergent boundary. Reverse Fault Example: Appalachian Mountains (East Coast) Questions • Explain the difference between a normal and reverse fault Questions • Explain the difference between a normal and reverse fault – A reverse fault is formed at a convergent boundary and creates mountains. A normal fault is formed with divergent boundaries and forms valleys Worst Earthquakes in the US • New Madrid fault on the Mississippi River in 1811 • 8.1 Magnitude • Epicenter in northern Arkansas • 35% chance of another major earthquake in the next 50 years New Madrid, MO