monitoring earthquakes chapter 2, section 3. did you know? the problem of predicting earthquakes is...
TRANSCRIPT
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Monitoring Earthquakes
Chapter 2, Section 3
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Did you Know? The problem of predicting Earthquakes is one of the many scientific questions that remains unsolved!
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It is important for scientists to develop ways to predict earthquakes because:
• A warning allows people who live in the area to protect themselves by:
– Reinforcing buildings and other structures– Getting emergency supplies– Evacuating
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• Earthquakes are dangerous, so scientists are trying to monitor them (monitor =watch closely)
What do scientists use to monitor and measure Earthquakes now?
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SeismoGRAPH• The machine that measures earthquake
seismic waves
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The Seismograph
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The Seismograph
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The Seismograph
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Seismic Waves cause the seismograph’s drum to vibrate
• The suspended weight with the pen attached to it moves very little
• Pen stays in place and records the drum’s vibrations
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Review: Which part of the Seismograph is moving?
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The part of the Seismograph that is moving is the rotating drum
http://www.youtube.com/watch?v=Gbd1FcuLJLQ
Modern-day Seismographs are digital and these are called “SeismoMETERS”
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Seismogram
• The pattern of lines that show a record of an earthquake’s seismic waves
• Seismograms are produced by the Seismograph machine
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SeismoGRAM –the written record of the seismic waves
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Look for the P waves, S waves, and Surface waves
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Seismic Waves on the Seismogram
• P waves –fastest and arrive first
• S waves –arrive shortly after p waves
• Surface waves –move the most slowly and produce the LARGEST disturbance on the seismogram
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In order to predict WHEN earthquakes are going to happen, where do you think is the first place that Geologists look?
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Geologists monitor FAULT LINES
• WHY?
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Geologists hypothesize that along a fault, they can monitor the stress buildup in the crust to predict when an earthquake might
occur
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Geologists measure the STRESS in the Earth’s crust on either side of faults, looking for:
• a slight rise or fall in the elevation (height) of the crust
• the tilt of the crust
• and the distance of horizontal ground movement
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Instruments for Monitoring Faults
• Tiltmeters
• Creep Meters
• Laser-Ranging Devices
• GPS Satellite
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1) Tiltmeter
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Tiltmeters
• Measures the “tilting” or lift of the crust on either side of the fault
• Consist of two contraptions that are filled with liquid and connected by a hollow stem
• If the land rises or falls slightly, the liquid will flow from one contraption to the other
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What type of faults are Tiltmeters used for?
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Used on NORMAL and REVERSE Faults
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2) Creep Meter
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Creep Meter
• Uses a wire stretched across a fault to measure horizontal movement of the ground
• One side of the fault, the wire is anchored to a post
• On the other side, the wire is attached to a weight that can slide if the fault moves
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Creep Meters
• Used on Strike-Slip Faults
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3) Laser-Ranging Devices
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Laser-Ranging Device
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Laser-Ranging Device
• Used on Strike-Slip faults
• Uses a laser beam to detect horizontal fault movements
• The device times a laser beam as it travels to a reflector and back
• The device can detect any change in distance to the reflector
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4) GPS Satellite
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GPS (Global Positioning System)
• Scientists can monitor changes in elevation AND horizontal movement along faults
• Scientists can see changes in elevation and horizontal movement
• Used for Normal, Reverse, and Strike-Slip Faults
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The movement along faults depends on how much friction there is between the sides of the fault
• Friction: the force that opposes the motion of one surface as it moves across another
• Low Friction = no Earthquake • Moderate Friction = small Earthquake• High Friction = big Earthquake
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Did You Know?
• Even with data from many sources, geologists cannot predict when and where an Earthquake will strike
• Reasons: – Sometimes stress builds up along a fault, but an
Earthquake does NOT occur – Sometimes an earthquake relieves stress in an
unexpected part of a fault
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The problem of predicting Earthquakes is one of many scientific questions that remains unsolved!