Earthquakes

Tremors and Earthquakes Earth’s crust is always moving. Tremors are movement in the crust that you may or may not feel. Earthquakes are sudden, strong shaking in the crust that causes a lot of damage. Where earthquakes start deep in the Earth’s crust below the surface is called the focus. On the surface directly above the focus is the epicenter, where it shakes the most on the surface.

The Cause of Earthquakes Plate movement generates forces at boundaries between tectonic plates Rocks respond to these forces in different ways Called stress, strain, and strength This depends on the rock type and the temperature and pressure at the time of deformation

Stress What is a force? Any push or pull Stress - is the local force per unit area that causes rocks to deform What is a force? Any push or pull Stress causes a deformation of the rock A.K.A. Strain Measurement of amount of change Breaking, folding, tilting, bunching up

Types of Stress Tension Compression Shearing

Earthquakes An earthquake occurs when brittle rocks being stressed suddenly fail along a geologic fault

Earthquakes Fault – a break or a crack in the earth along which movement occurs

Types of Faults Normal Fault Caused by tension

Types of Faults Reverse Fault Cause by compression

Types of Faults Caused by shearing A.K.A. Strike Slip Fault Lateral Fault Caused by shearing A.K.A. Strike Slip Fault

Earthquakes and Waves Every earthquake generates vibrations called seismic waves that travel out from the focus in all directions. (Imagine ripples in water) Seismographs measure these seismic waves, even tremors we cannot feel, and records them on a sheet of paper. The record produced by a seismograph is called a seismogram. - It is made up of wavy lines, the higher the wavy lines are the stronger the earthquake is. - It can tell a scientist how far the epicenter is and the force of an earthquake.

Types of Waves Primary waves, or P-waves, squeeze and pull rocks in the same direction along which the waves are traveling. -Fastest / First to reach seismograph -Move through solids, liquids, and gases

Types of Waves Secondary waves, or S-waves, cause rocks to move at right angles in relation to the direction of the waves. -Slower than p waves / second to reach seismograph -Only travels through solids

Earthquakes and Waves Surface waves travel along Earth’s surface, moving in two directions as they pass through rock. -Also called long waves or L-waves and are the slowest and travel through solids

Earthquake Magnitude and Intensity The Richter scale - a numerical scale based on the size of the largest seismic waves - Earthquakes are given a number between 1 and 9 The stronger the earthquake the higher the number For each numerical increase the energy released is 10 times more than the previous number. 7 or more causes a great deal of damage 2.5 or less is typically not felt by people Largest earthquake recorded was a 9.5

Damage Buildings can sway, topple over, or collapse Damage to electrical lines, phone lines, and water pipes Explosions and fires from broken electric and gas lines. Landslides

Tsunamis A large ocean wave caused by an earthquake. Out in the open ocean do not get very high. As they get closer to shore and the depth decreases the height of the wave increases.

Zones of Activity Most big earthquakes and volcanic eruptions occur in 3 areas or zones: - Ring of Fire: most active volcanoes on landmasses are located here. Western coasts of North and South America are part of it. - Mid-Atlantic Ridge: long underwater chain of volcanic mountains. New crust is formed here. Iceland is a volcanic island part of it. - Eurasian-Melanesian Belt: mountains here were formed when parts of Earth’s crust collided.