Key Concept: Seismic waves cause the seismograph’s drum to vibrate. But the suspended weight with the pen attached moves very little. Therefore, the pen stays in place and records the drum’s vibrations.
In a simple seismograph, a pen hangs down from a heavy weight. The point of the pen touches graph paper that is wrapped around a cylinder, or drum. As the drum turns, the pen draws a line on the paper.
When an earthquake shakes the ground, the pen hardly moves because of the weight. But the drum shakes with the ground. The shaking of the drum makes the line on the paper jagged. The more jagged the line is, the stronger or closer the earthquake was.
Key Concept:To monitor faults,geologists havedeveloped instruments to measure changes inelevation,tilting of the land surface,and groundmovements along faults.
Ground movements near a fault are a clue that anearthquake might happen.So scientists measuregroundmovements near faults.They use tiltmeters,creep meters, and GPS satellites.
Tiltmetersshowhowmuch the ground is tilting, ortipping.A tiltmeter works like a carpenter’slevel.Whenthe groundtilts,water inside a glass bulbshowshowmuch tilting there is.
Creep meters showhowfar the sides of a faulthavemovedinoppositedirections.Acreepmeterusesawirestretched across the fault.The wire gets longer whenthe two sides moveapart.
Scientists put markers along both sides of a fault.GPSsatellites detect tinymovements of the markers in anydirection.
Why do scientists measure ground movements near faults? a. Ground movements are a clue that an earthquake may happen. b. Ground movements show that an earthquake is over. c. Ground movements show that rocks are no longer under stress.
Creep meters GPS Satellites
Key Concept:Seismographs and fault-monitoringdevicesprovide data used to map faults and detectchanges along faults.Geologists are also trying touse these data to develop a method of predictingearthquakes.
When seismic waves reach a fault, they bounce off it, like a ball bouncing off a wall.
Seismographs record the waves that bounce back. Scientists can use the seismographic data to find the fault.
Seismographic data can also be used to learn how easily rocks move at a fault. At faults where rocks do not move easily, stress builds up, and big earthquakes are likely.
Even with data from many sources, scientists cannot predict exactly where or when an earthquake will happen.
Circle the letter of the choice that describes where bigearthquakes are likely to happen. a. at faults where rocksmove easily b. at faults where rocks do not move easily c. at rocks where there are no faults
true or false? Scientists cannow predict exactly where and when earthquakes will happen. False