An earthquake is ground movements that occur when blocks of rock in Earth move suddenly and release energy.

Earthquakes occur along fault lines.◦ Faults are breaks in Earth’s crust where blocks of

rock slide past each other. As the plates move, pressure builds up near

their edges, causing fault lines.

The Focus is the place beneath Earth along a fault line where a block of rock breaks causing an earthquake.

The Epicenter is the exact spot on Earth’s surface directly above the focus.

A wave is a disturbance in an substance that transports energy from one place to another.

Seismic waves are vibrations given off by Earthquakes that cause ground movements. ◦ When blocks of rock break, the released energy

travels in seismic waves.

Body waves (travel through Earth)◦ P waves (primary waves) travel through solid,

liquid, and gas because they move in a back and forth direction (slinky). fastest

◦ S waves (secondary waves) can only travel through solids because they move up and down. Second Fastest

Surfaces Waves◦ Only travel along Earth’s Surface. ◦ Travel back and forth and up and down. ◦ Slowest.

A seismograph is a tool used to measure the size of an Earthquake based on seismic waves.

The Richter Scale measures the ground motion of Earthquakes. ◦ A scale of 1-10 where each magnitude increase is

equal to 10 times the ground movement.

The moment magnitude scale◦ The modern rating system which measures the

energy output of an earthquake.

Mercalli Scale◦ Measures earthquakes by the amount of damage

they produce. (intensity)

Stress is pressure on a block of rock causing it to bend and break (caused by Earth’s plates).

Tension stress stretches rock, making it thinner. (occurs at Divergent Boundaries)

Compression stress shortens and squeezes rock. (occurs at Convergent Boundaries)

Shear stress pushes different blocks of rock past each other. (Occurs at Transform Boundaries)

◦ Faults are breaks in Earth’s crust where blocks of rock slide past each other.

Normal fault◦ Caused by tension and can be found at divergent

boundaries.

Reverse Fault Are a result of compression and can occur at

convergent plate boundaries.

Strike Slip Fault Caused by shearing and can be found at transform

boundaries.

The Law of Superposition◦ If rock layers are undisturbed, the youngest will

be on top. Rocks will get older the deeper you get into the crust.

◦ Sediments are continuously deposited on top of each other.

◦ If rock layers are undisturbed, the deeper you get the older the rocks, fossils, etc. are.

When rock layers are disturbed or changed, the oldest is not always found on the bottom. ◦ Folding, faulting, and the rise of magma change

rock layers. ◦ Anytime igneous rocks cut across sedimentary

rock layers, they are the youngest. ◦ This causes the law of superposition to be

incorrect at times.

The movement of Earth’s Plates and convection currents causes the rock cycle. ◦ Zones of subduction form magma, which rises

and creates igneous rocks. ◦ Zones of subduction also create metamorphic

rock, exposing rocks to extreme heat and pressure.

◦ When mountains are formed, they will weather, creating sediments and sedimentary rock.