The Earth is always moving.
Large shifts in the Earth's crust cause cataclysmic earthquakes all over the world. But smaller shifts in fault lines occur all the time. Geologists study these smaller shifts, hoping to learn how and when earthquakes occur. Geologists hope that with enough data, they may someday be able to predict earthquakes in much the same way meteorologists predict storms. Measuring seismic shifts takes a wide variety of equipment.
Creepmeter
A creepmeter measures seismic movement with a simple wire. A wire stretches over a fault line and attaches to two firmly planted piers. Electrical and mechanical measurements show the relative change between the two piers as the fault slips. Creepmeters require multiple years of data. They have cyclical patterns as their rock base expands and contracts with the seasons.
Magnetometers
Magnetometers measure the fluctuations in the magnetic fields of the earth's crust. As stress grows around a fault line, heat builds up, changing the magnetic nature of the underlying minerals. Magnetometers must be carefully placed and maintained. Machinery, power lines and even cell phone towers all affect magnetometers, so they must be placed in isolated areas. Data obtained must be corrected for changes in the Earth's magnetic field as well as solar and magnetic storms that occur from time to time.
Strainmeter
The strainmeter consists of a stainless steel tube surrounded by a ring filled with silicone oil. The ring is split into three independent sections. Inserted up to 200 meters below the surface of the earth, the strainmeter is cemented firmly into place. As seismic shifts occur, the srainmeter records the pressure on each section of its oil-filled ring and sends the data to the surface to be analyzed.
Tiltmeters
Tiltmeters measure changes in the Earth's horizontal plane. There are two major types of tiltmeters, both using boreholes drilled near a fault line. The simplest tiltmeter is simply a pendulum. The pendulum lies underground surrounded by a charged plate. When the earth changes position enough, the pendulum shifts and touches the plate. A signal alerts the geologist to the subtle seismic change. The second type of tiltmeter resembles a carpenter's level. Oil or water, placed in a clear tube, is inserted deep below the earth. Cameras and mirrors give the geologist a clear view of the level. He records all changes.
Ocean Acoustic Monitoring
Earthquake survivors know that earthquakes make a lot of noise. On the surface, the sound of minor tremors are drowned out by everyday noise. But under water, the scraping sound of one plate as it moves against another is magnified. A variety of different microphones all over the planet listen for the sound of earthquakes. Sonobouys dropped by airplane record the sounds of earthquakes and marine animals in remote areas. The U.S. Navy maintains SoSus, or the Sound Surveillance System. This system, designed in the early 1970s during the Cold War, links arrays of cabled microphones. The system that once listened for enemy subs now gives geologists new ears for underwater seismic shifts.
Tags: fault line, seismic shifts, changes Earth, smaller shifts
