What exactly is an earthquake?
The average length of an earthquake is from 30 to 60 seconds. An earthquake is the shaking and trembling that results from the movement of rock beneath the Earth’s surface. If friction between two blocks of rock is low, the rocks slide constantly without sticking. If the friction is high, the blocks lock together. When the amount of stress is greater than the amount of friction, the blocks unlock suddenly, setting off an earthquake! The average length of an earthquake is from 30 to 60 seconds.
What is this stress that causes Earthquakes What is this stress that causes Earthquakes? (Can rocks get stressed out?) Stress is the force that acts on rock to change its shape or volume. Stress adds energy to the rock. The energy is stored in the rock until it changes shape or breaks. The change in the shape or volume of the crust is called deformation.
Tension Compression Shearing What are the three types of deformation that stress can cause on rocks? Tension Compression Shearing Tension Compression Shearing
Tension Stress Stress that pulls on the crust, stretching rock. This stress causes the middle of the rock to thin out. This stress is associated with which type of plate boundary? Divergent
Compression Stress Stress that squeezes rock until it folds or breaks. This stress is associated with which type of plate boundary? Convergent
A portion of the San Andres Fault is Compression Stress!
Shearing stress transform Stress that pushes a mass of rocks in two opposite directions This type of stress is associated with which type of plate boundary? transform
What are folds? A fold is a bend in rock that happens from compression. This stress causes the middle of the rock to bulge.
What are the different kinds of folds? A fold that bends in the middle is called an anticline. (think of an ANT hill!) A fold that bends in the middle is called a syncline. (think of it as a sink-line!) upward Downward
More information about anticlines: The tops of anticlines get weathered and eroded away to become mountains. Weathered and eroded folds create chains of parallel mountains and hills. Anticlines are where scientists search for oil deposits because impermeable rocks trap oil in the permeable rocks below it.
What is a fault? When stress builds up in rocks, it fractures. This fracture in the Earth’s crust is known as a fault. (The Earth is cracking under so much stress!)
There are 3 Main Types of Faults Normal fault Reverse fault Strike-slip fault
Normal Fault Normal faults are caused by tension. One block of rock lies above the fault, the footwall. The other block, the hanging wall, lies below it.
Reverse Fault Reverse faults are cause by compression. In this fault, the hanging wall slides upward past the footwall. Also known as a Thrust Fault
Strike-slip Fault Shearing causes strike-slip faults. The rocks on either side of the fault slide past each other in the opposite direction.
What are some other landforms created by faults? When normal faults uplift a block of rock, a fault block mountain forms. The hanging walls from both normal faults, drop, they leave a block of mountains in the middle. A plateau is a large area of flat land elevated high above sea level. If a fault pushes up a large flat block of rock, a plateau can form. Over millions of years, fault movement can change a flat plain into a towering mountain range.