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AIM: How are earthquakes monitored? OBJ: Given notes and activity sheet SWBAT explain how a seismograph works, how fault activity is monitored and how seismographic data is used with 70% accuracy DN: Watch video: https://www.youtube.com/watch?v=kXrftpP-bRY HW Check- Earthquakes & Seismic Waves ACT: Introduction to seismograph, monitoring faults, and using seismographic data. Text, read, p. 60-65, Work on Monitoring Earthquakes HW: Complete Monitoring Earthquakes Activity Sheets; Work on Tectonics Activity Sheets, Tectonics Exam, Friday, February 13. Seismograph: instrument used to measure seismic waves (earthquake movement/vibrations) Seismic waves cause the seismograph’s drum to vibrate.The suspended weight with the pen remains stationary while the drum records the vibrations. The pen remaining stationary occurs due to a basic principle of physics, “every object resists any change to its motion”. Seismogram: a record of an earthquake’s seismic waves. The height of the jagged line represents the magnitude (strength) of the earthquake. Seismograph & Seismogram Instruments that Monitor Faults: Change in elevation and tilt of the land is related to the build up of stress in the rocks. Increasing stress eventually results in an earthquake. To monitor fault activity, a variety of devices are used: Tiltmeter: measures vertical movement (tilting or raising of the ground); ex: carpenter’s level Creep Meter: measures horizontal movement of the ground across a fault. Laser Ranging Devices: measures long distance horizontal movement. GPS Satellites: monitor changes in elevation, tilt of the land and horizontal movements along a fault with great precision. Tilt Meter Creep Meter Using Seismographic Data: Seismogram and fault monitoring data are used to map active faults, monitor changes along faults and develop a method of predicting earthquakes. Mapping Faults: faults can be hidden by a thick layer of rock or soil. Seismic data helps to map fault length and depth so that the earthquake risk for an area can be determined. Monitoring Changes Along Faults: Friction: is the force that opposes the motion of one surface as it moves across another surface. If friction is low, the stress is low and a major earthquake is unlikely. If the friction is high, the rocks lock together, the stress increases until an earthquake occurs. 3D Fault Model Predicting Earthquakes: Geologist’s can not predict when and where an earthquake will strike. Usually, stress increases along a fault until an earthquake occurs. But sometimes the earthquake doesn’t occur or one or more quakes occur along subsidiary parts of the fault. Predicting an earthquake remains an uncertain science.