Earthquakes

What is an earthquake? Earthquake: a sudden release of energy in earth’s crust that causes movement

Why Earthquakes happen Friction prevents movement along a fault Fault: a fracture in a rock formation where movements occurs Sudden release causes a quake

Elastic Rebound Elastic rebound: the sudden return of deformed rock to its original position

Fence offset 8 1/2 feet by main fault in rural California1906.

Anatomy of an Earthquake Focus: the location within Earth along a fault at which the first motion of an Earthquake occurs The shallower the focus, the more destructive the quake

Anatomy of an Earthquake Epicenter: the location on Earth’s surface directly above the focus

Seismic Waves Seismic Waves: Vibrations caused by earthquakes

Body Waves Body waves: seismic waves that travel through earth’s interior Two types: Primary waves: P-waves- Fastest and the first to be detected Can move through solids, liquids, or gas

Body Waves continued Secondary waves: S-waves- shake the ground back and forth (2 nd fastest) Can move through solids ONLY

Animation

Surface waves Surface waves: Only move along the surface of Earth Slower, but cause the most damage

Surface Waves Love waves: fastest surface waves Move rock side to side

Diagram of love wave

Surface Waves  Rayleigh waves: also called a “ground roll”  Moves rock in a circular motion

Seismic Waves and Earth’s Interior The composition of the material a seismic wave moves through affect their speed and direction Andrija Mohorovicic (1909): used seismic waves to find the depth of the mantle

Seismic Waves and Earth’s Interior Shadow Zones: locations on Earth’s surface where no body waves from a particular earthquake can be detected animation

Seismic Waves and Earth’s Interior P-waves are bent as they pass through different layers S-waves are blocked by the liquid outer core because they can only travel through solids

Activity 1: Seismic Waves Reflection and extension quiz

Studying Earthquakes Seismograph: an instrument that detects and records seismic waves Seismogram: the recorded tracing produced by a seismograph

Studying Earthquakes (cont.) Different waves move at different speeds: P-waves arrive first, then S-waves, then Surface waves

Locating an Earthquake The longer the lag time between P-waves and S-waves, the further away the earthquake is The location of an earthquake can be found by triangulation: using the distance from 3 stations to find the epicenter of the earthquake earth_science/terc/content/investi gations/es1003/es1003page02.cfm ?chapter_no=investigation

Measuring Earthquakes Magnitude: the strength of a quake

Measuring Earthquakes Richter Scale: assigns a number to define the energy released during an earthquake utube.com/watc h?v=wVqYg4NP vC4https:// utube.com/watc h?v=wVqYg4NP vC4 richter scale explained

outube.com/w atch?v=1qbg7 orb1lc Bill nye

Measuring Earthquakes Big numbers = stronger earthquakes Taiwan (1999)

Measuring Earthquakes Intensity: the amount of damage caused by an earthquake

Tsunamis videos/tsunami videos/tsunami-101

Tsunamis Tsunami: a giant wave caused by an earthquake on the ocean floor

Earthquake Safety

Earthquakes are more likely to happen in some places, but can happen anywhere Before: have supplies on hand Such as: food, water, flash lights, batteries, radios and a first aid kit During: stand in a doorway, stay away from windows and tall things Protect your head from falling objects Drop, Cover and Hold On After: be cautious of fires, downed powerlines, etc. Remove yourselves from buildings and check for structural damage. e01.cfm?chapter_no=visualization

Earthquake Warnings/Forecasts Scientists study past quakes to predict where future quakes are most likely to occur There is No reliable way to predict when or where an earthquake will happen When stress is building up in rock, sensors can detect tilting and cracking Foreshocks usually happen before a large earthquake