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Transcript
Chapter 6, section 2 Seismograph → X Seismic waves → Recording Earthquakes Seismograph- an instrument that detects and records seismic waves Seismogram- chart made by a seismograph in response to a earthquake Earthquakes produce three types of waves. Each waves travels at a different speed and causes the Earth’s crust to move in different ways: 1) P waves (primary waves) Moves the fastest and are first to be recorded by a seismograph Moves through solids and liquids Moves by squeezing and stretching (like a slinky) 2) S waves (secondary waves) Moves more slowly and are second to be recorded by a seismograph Can only move through solids Moves up and down (like a rope) X 3) Surface waves (long waves or L waves) When P and S waves reach Earth’s surface their energy is converted into surface waves Moves the slowest Only travels on Earth’s surface Causes the greatest damage Can move back and forth or up and down Locating an earthquake → In order to determine the epicenter of an earthquake scientists need a seismogram from at least 3 seismograph stations 1) Determine the elapsed time between the arrival of the P wave and the arrival of the S wave 2) Use a ‘time-distance graph’ to determine the distance from the station to the earthquake (P and S waves always travel at the same speed) 3) On a map, draw a circle around the epicenter. Radius= distance to the epicenter 4) Repeat for the two other seismic stations 5) The point where the three circles meet is the location of the epicenter X Measuring earthquakes → X 1) Richter Scale- measures the magnitude of an earthquake (the amount of energy released by an earthquake) o Magnitude is determined by measuring the amplitude of the largest wave o Each whole number on the Richter scale is ten times greater in wave amplitude than the number below (and releases about 32 times more energy) 2) Mercalli Scale- measures the intensity of an earthquake (the amount of damage it causes) o The scale ranges for I (felt by few people) to XII (total destruction) o Less scientific because the intensity changes depending on the distance to the epicenter, building quality, and ground material X X