Wednesday January 2, 2013 What is an earthquake? (yes, I will be checking your answers!)

An earthquake is a shaking of the ground caused by the sudden breaking and shifting of large sections of Earth's rocky outer shell. What is an Earthquake? The movement of the Earth’s plates creates powerful forces that squeeze or pull the rock in the crust. These forces are examples of stress.

The three types of boundaries

Types of stress Shearing Tension Compression The crust is pulled, stretching the rock thinner in the middle. The rock is squeezed until it folds or breaks. Rock is pushed in opposite directions causing a break or slip

When enough stress builds up in rock, the rock breaks, creating a fault. A fault is a break in the crust.

There are 3 types of faults 1 Strike-slip faults : this is where the rocks slide past each other. This occurs along transform boundaries. (EX. The San Andreas fault)

There are 3 types of faults 1 Normal Faults : this is where tension forces cause one side to rise above the other. This happens along divergent boundaries (EX. The Rio Grande rift valley).

There are 3 types of faults 3. Reverse Faults: this is where compression forces cause one side to rise above the other. Often times mountains are formed along these faults. (EX. The Appalachian mountains)

Friction Where friction is low, the rocks slide past each other easily. Where friction is moderate, the sides jam and jerk producing small earthquakes. Where friction is high, the rocks lock together. Stress builds until a major earthquake occurs.

Where do earthquakes occur? Most earthquakes occur along plate boundaries or stress points.

The latest seismic activity

Measuring Earthquakes Seismic waves are vibrations that travel through Earth carrying energy released during an earthquake. They travel from the focus, through the Earth’s interior, and across the surface. The epicenter is the point on the Earth’s surface directly above the focus.

Seismic Waves P waves or primary waves cause the ground to compress and expand like an accordion. P waves are the fastest seismic waves. And they can travel all the way through the earth. P waves create a push/pull effect.

Seismic Waves S waves or secondary waves cause the ground to shake up and down. These waves can only travel through solid material, thus when the waves hit the outer core they stop.

Seismic Waves –Surface waves are the third type of wave. –These are the waves that produce the most destruction. –Surface waves are limited to travel along only the surface of the Earth.

Measuring Earthquakes A seismograph records the ground movement caused by seismic waves. The magnitude is the measurement of the earthquake strength based on the seismic waves and movement along faults.

SCALES The Mercalli scale was developed to rate earthquakes according to their intensity. It is not as accurate as the... The Richter scale is a rating of the size of seismic waves measured by a seismograph. The Moment Magnitude Scale is a rating system that estimates the total energy released by an earthquake. It is the most accurate. Charles Richter

Mountain building Mountains formed by faulting are called fault-block mountains These mountains are formed when two normal faults mirror each other. Mountains and valleys are formed in this way. The Great Basin

Mountain building Folds are bends in rock that form when compression forces are present. Collision of plate boundaries can cause folded mountains. These collisions can lead to earthquakes due to faults produced. The Himalayas and the Alps

Anticlines and Synclines These terms describe the folds in the rock. A fold that bends upward into an arch is an anticline. A fold that bends downward to form a bowl is a syncline.