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Earthquakes Ch.6 Faults • Pg. 86 • Faults shift due to stress from surrounding rock. 6.1 Earthquakes and Plate Tectonics • Earthquakes – vibrations of the earth’s crust • -caused by the shift in a rock because of stress in along a fault • Locked - Friction holds the fault together for awhile • 1. Elastic rebound theory • 2. Major Eathquake zones Elastic rebound theory • • • • • • • • • • • • The rock under stress springs back to its original shape after separating at weakest point of the fault The rocks on each side of a fault are moving slowly. Stress builds until the rocks fracture at the weakest point. Which causes the rocks to break and spring back to their original position. If the rocks are “locked” stressed builds. Seismic waves – energy released in vibrations as rocks slip into new positions causing the ground to shake. Aftershocks – small tremors Focus – area of slippage first (shallow underground) within 4 miles Epicenter point on the surface above the focus Lots of Energy and damage to surface with shallow focus Aftershocks p.1 • After the initial breakage of rock causing an earthquake, other areas around it give off smaller waves called aftershocks. Focus of an Earthquake p.2 • The area along a fault where the slippage first occurred. Epicenter p.2 • The point on the earth’s surface directly above the focus. Focus Depths p. 2 • 90 % of all earthquakes happen near the surface. • Less than 70 km down. • Why do you think this is? Answer • The deeper you go down in the earth the hotter it is. • Making the rock like playdough. • They mush together a faults and don’t snap causing vibrations. Major Earthquake zones • Pacific Ring of Fire • Midocean ridge • Eurasian-Melanesian belt • Fault zones Earthquake zones Major Earthquake Zones p.3 1. Pacific Ring of fire - see page 101 - plates are subducted – causing stress resulting in earthquakes. 2. Along mid-ocean ridges - divergent plates push outwards and creates stress. 3. Eurasian-Melanesian Mountain Belt - Convergent plates – they hit and stress cause Why Then Does Missouri and Tennessee Have Earthquakes? • They are not on a plate boundary? 1970 they found an ancient fault buried under sediment. Fault formed 600 million years ago. 1812 big quake Homework • page 102 # 1-4 • 1. 2. 3. 4. Draw an earthquake. Label: Epicenter Focus Pick a fault type and use it Draw the seismic waves 6.2 Recording Earthquakes • • • • Seismograph – 3 electric sensing devices 1 vertical 2 horizontal Mechanical energy to electric on magnetic tape • 1. types of seismic waves • 2. Locating an earthquake • 3. earthquake measurement 1. types of seismic waves • P waves – primary waves, fastest, 1st recorded, solids and liquids, more ridgid the rock - faster • S waves – secondary waves, only solid material, moves at right angles, doesn’t make through the core to other side of earth • Surface waves – slowest moving causing the ground to rise and fall 2. Locating an earthquake • • • • 3 plots P waves S waves Surface waves 3. earthquake measurement • Magnitude – ground motion or amount of Energy released • Richter scale • Microquakes – less than 2.5 magnitude • Mercalli scale – expresses the intensity of an earthquake, or the amount of damages it causes I - XII Earthquake 20 min. Seismic Waves p.4 • When an earthquake occurs energy in the form of seismic waves is given off. These waves are what causes the rocks to be stressed, break, and snap back. (ERT) Seismograph 3 Types of Seismic Waves p.5 1. Primary waves or P waves - move the fastest - are the first to be recorded by a seismograph - can go through solids and liquids - the more rigid the material the faster a P wave can travel Types of Seismic Waves cont..p.6 2. S waves - Can travel only through solids - can not go through the liquid outer core 3. Surface Waves - when P or S waves reach the surface (crust) -causes the surface to rise and fall - really destructive when traveling through loose soil Locating Earthquakes • Like thunder and lightning • P waves are 1.7 times faster than S waves. • They record how far apart the P and S waves are recorded – tells them how far away the epicenter is located. • 3 seismograph stations needed - pg 104 - 3 circles Measuring Earthquakes • Magnitude – the measure of the energy released by an earthquake. - also the amount of ground movement Scales Used to Measure Earthquakes p.7 • Richter scale – a number describing how big the earthquake is 7 or above – major earthquake - wide spread damage 6-7 moderate earthquake 2.5 – 6 minor earthquake under 2.5 – called a microquake – not felt by people Mercalli Scale p.8 • Measures the intensity or amount of damage an earthquake caused • Uses roman numerals I through XII I not felt by people X total destruction Homework • Page 105 # 1-5 Earthquake Damage 6.3 Injuries/Death p.9 • Most injury and death is not from the ground shaking it is from buildings/structures collapsing. Other Problems from Earthquakes p.9 • Fire from broken gas lines • Dams break Buildings Collapse p.9 • Buildings on loose soil are effected more - the ground acts like jello and shakes more violently • Tall buildings sway, collapse, or tip over as the ground shakes Earthquake safety • Being in an open field or area is safest • If in your house stay away from shelving and windows. • Stand inside a doorway Why would this be the safest spot? Buildings and safety • In Tokyo and the bigger cities in California build their buildings that can “sway” without falling. • The base of the building is the key. Irregular shapes / rubber type material Absorbs seismic waves =less damage Earthquake Warning/Predictions • They are hard to predict which means we can’t warn people to get to safety • Possible warnings Right before an earthquake some animals will act restless or nervous. Scientific Warning/Predictions • Scientists can look at seismic gaps. These are areas along faults that have been locked and are experiencing stress. Which means it can snap! Page 111 figure 6-7 Homework • 6.3 Review 1-5 pg. 111 • Review pp. 112-113 1-14 • Testbank 1-24 Tsunamis Tsunamis p.10 • A major earthquake with an epicenter on the ocean floor that causes a giant wave. • The ocean crust breaks and along the fault it causes a rise or fall in the sea floor. When it rises or falls the water gets pushed up in the form of a wave. Video- click on it. 2004 Tsunami • The 2004 Indian Ocean earthquake, was an undersea earthquake that occurred at 00:58:53 UTC (07:58:53 local time) December 26, 2004, with an epicentre off the west coast of Sumatra, Indonesia. The earthquake triggered a series of devastating tsunamis along the coasts of most landmasses bordering the Indian Ocean, killing more than 225,000 people in eleven countries, and inundating coastal communities with waves up to 30 meters (100 feet). This was the ninth-deadliest natural disaster in modern history. Indonesia, Sri Lanka, India, Thailand, and Myanmar were hardest hit. • With a magnitude of between 9.1 and 9.3, it is the second largest earthquake ever recorded on a seismograph. This earthquake had the longest duration of faulting ever observed, between 8.3 and 10 minutes. It caused the entire planet to vibrate as much as 1 cm (0.5 inches)[1] and triggered other earthquakes as far away as Alaska.[2] • The disaster is known by the scientific community as the Great Sumatra-Andaman earthquake,[3] and is also known as the Asian Tsunami and the Boxing Day Tsunami. The tsunami occurred exactly one year after the 2003 Bam earthquake and exactly two years before the 2006 Hengchun earthquake. • The plight of the many affected people and countries prompted a widespread humanitarian response. In all, the worldwide community donated more than $7 billion (2004 U.S. dollars) in humanitarian aid. Homework • Page 112-113 #1-14 Critical thinking #1-4 Application #1,2