Monitoring Earthquakes 6.3 p.178-183
Detecting Earthquakes • As early as 2000 years ago the Chinese had developed an instrument to detect earthquakes. • The modern day instrument is a seismograph. A seismograph is a heavy weight attached to a frame by a spring or wire. A pen is connected to the weight and rests on a drum covered by paper. As the drum rotates the pen writes on the paper.
Seismograms • When an earthquake occurs the paper makes a picture of graph of the earthquake. These zigzag patterns are called, • P,S and Surface waves all show up differently on seismogram. See p. 179
Other Earthquake instruments • Scientist sometimes place other instruments in earthquake prone areas. • Tiltmeters: measure the tilt or raising of the ground (measure vertical movement) works like a level. • Creep meters: uses a wire that is stretched across a fault attached to a post and measures horizontal movement when other end shifts. • Laser-ranging devices: laser beams detect horizontal movement. Laser strikes a reflector and then bounces back. If reflector moves they are notified.
GPS Satellites: markers are set up and using GPS the elevation and any movement can be detected with satellites. • Why do they want all this data? To try to predict when earthquakes will occur and where.
Mapping/monitoring Faults • Mapping all the faults is crucial to know where an earthquake will occur. • They then monitor friction. The amount of friction built up in an area will determine how big the earthquakes will be. • Hardly any: no stress and rarely any big earthquakes • Moderate friction: small earthquakes • High friction: big earthquakes