Monitoring Earthquakes Chapter 2, Section 3
Did you Know? The problem of predicting Earthquakes is one of the many scientific questions that remains unsolved!
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
Earthquakes are dangerous, so scientists are trying to monitor them (monitor =watch closely) What do scientists use to monitor and measure Earthquakes now?
SeismoGRAPH • The machine that measures earthquake seismic waves
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
The part of the Seismograph that is moving is the rotating drumhttp://www.youtube.com/watch?v=Gbd1FcuLJLQModern-day Seismographs are digital and these are called “SeismoMETERS”
Seismogram • The pattern of lines that show a record of an earthquake’s seismic waves • Seismogramsare produced by the Seismograph machine
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
In order to predict WHEN earthquakes are going to happen, where do you think is the first place that Geologists look?
Geologists hypothesize that along a fault, they can monitor the stress buildup in the crust to predict when an earthquake might occur
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
Instruments for Monitoring Faults • Tiltmeters • Creep Meters • Laser-Ranging Devices • GPS Satellite
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
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
Creep Meters • Used on Strike-Slip Faults
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
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
The movement along faults depends on how much frictionthere 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
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
The problem of predicting Earthquakes is one of many scientific questions that remains unsolved!