Earthquakes

vocabulary Stress- a force that acts on rock to change its shape or volume. Adds energy to the rock. Stores energy until rock changes shape or breaks. Stress occurs slowly by shifting of Earth’s plates and cannot be observed

Types of stress Tension Compression Shearing

tension Stretches rock so it becomes thinner in the middle (pulling apart a warm piece of bubble gum) Occurs when 2 plates are moving apart

Compression Squeezing of rock until it breaks (like a trash compactor) Plates pushing against each other

Shearing Pushing of rock in opposite directions Can cause rock to: Break Slip apart Change shape

Faults-what causes them? Stress build up to the point the rock breaks A fault is exactly that……a rock that breaks Rock surfaces slip past one another Can move up, down, or sideways

Faults 3 kinds Normal Reverse Strike-slip

Normal faults Fault is at an angle “stretches” rock Tension is force causing this One rock lies above the fault (hanging wall), one below the fault (footwall) Hanging wall slips downward Occurs where plates divergent boundary

Reverse Fault Rock of crust is pushed together Compression causes reverse faults to form Same as normal fault but blocks move in opposite direction Hanging wall slides up and over the footwall Formed the Rocky Mountains Convergent boundary This Photo by Unknown Author is licensed under CC BY-SA

Strike-Slip Faults Plates move past one another or “shears” one another Move past one another sideways Forms a transform boundary San Andreas fault in CA is an example

US fault lines

Earth’s surface changes-Folding There are “folds” in rock Anticline=(arch) A fold that bends upward into an arch (like a mountain) Syncline=(sags) A fold that bends downward to form a valley Himalayas and Alps