Earthquakes Types of stress: Tension – Stress that stretches and pulls rocks. It happens when two plates move apart. Compression – The stress that squeezes rocks. It happens when rocks push together. Shearing – Stress that pushes rocks in opposite direction. Happens when plates slide past each other

Earthquakes Kinds of Faults: In many faults the fault line is slanted

Earthquakes Kinds of Faults: Normal Fault – Happens when tension pulls rocks apart. The hanging wall slips down.

Earthquakes Kinds of Faults: Reverse fault – When compression pushes rocks together. The hanging wall slides up and becomes higher than the footwall.

Earthquakes Kinds of Faults: Strike-Slip Fault – Happens when shearing pushes rocks in different directions. Sections of rock slide past each other horizontally.

Earthquakes Changing Earth’s Surface: Compression of Earth’s surface causes folding Anticlines – Folds that bend upward into ridges Synclines – Folds that bend downward into valleys

Earthquakes Changing Earth’s Surface:

Earthquakes Earthquakes and Seismic Waves: Earthquake – The shaking that occurs when rocks move inside the Earth. Focus – The place where rocks break and cause an earthquake. Epicenter – The point on the surface directly above the focus.

Earthquakes Types of seismic waves: P Waves – Moves rocks back and forth like a spring. Fastest waves.

Earthquakes Types of Waves: S Waves – Moves rocks up and down. Slower than P waves, but do more damage.

Earthquakes Types of waves: Surface waves – Combined P and S waves that travel along the surface. They are the slowest, but do the most damage.

Earthquakes Measuring Earthquakes: Mercalli Scale – Based on the amount of damage done. Uses Roman numerals I – XII to rank the damage. (See figure 9 in book) Richter Scale – Based on the size of the seismic waves. A seismograph is used to measure seismic waves. Does not work well for large or distant earthquakes.

Earthquakes Measuring Earthquakes: Moment Magnitude Scale – Based on the amount of energy an earthquake releases. (Includes seismic wave size)

Earthquakes Locating the Epicenter: P waves are faster than S waves The longer it takes for the S waves to reach the seismograph after the P waves, the further the epicenter is away. Three seismographs are used in different location to locate an epicenter.

Earthquakes

Earthquakes Monitoring Earthquakes: The Seismograph – A drum vibrates when seismic waves reach it as a suspended weight with a pen attached records the vibrations.

Earthquakes Instruments that Measure faults: Tiltmeters – Like a level that measures the shift of land.

Earthquakes Instrument that Measure faults: Creep Meters – Uses a wire stretched across a fault to measure horizontal movement. Laser-Ranging Devices – Uses a laser beam to detect horizontal movements. GPS Satellites – Bounces radio waves off receivers on the ground to pinpoint small changes in tilt and horizontal movement of a fault.

Earthquakes

Earthquakes Using Seismographic Data: We use data from different monitoring devices to: map faults 2. monitor changes along faults (like how much friction) 3. Try to predict earthquakes

Earthquakes Earthquake Safety: Geologists can determine earthquake risk by locating where faults are active and past earthquakes have occurred.

Earthquakes How Earthquakes Cause Damage: Shaking – Causes landslides and avalanches. Loose soil shakes more than rock. Liquefaction – The violent shaking can turn loose soil into liquid mud. Aftershocks – Buildings weakened by the initial quake can be finished off by the aftershocks. Tsunamis – Giant waves caused by under sea earthquakes.

Earthquakes Steps to earthquake Safety: Drop, Cover, and Hold If outdoors, go to an open area and sit down on the ground If you live in an earthquake area, have an earthquake kit that includes bottled water, canned food, and other emergency supplies (Like a First-Aid Kit)

Earthquakes Designing Safer Buildings: Newer buildings are built stronger and more flexible Older buildings need to be modified and reinforced (Fiberglass wrap) Base-isolated building – Rests on shock-absorbing rubber pads to reduce the energy that reaches the building. (Like suspension on a car)

Earthquakes