# Bellringer How many seismic stations are required to triangulate the epicenter of an earthquake?

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Bellringer How many seismic stations are required to triangulate the epicenter of an earthquake?

Monitoring Earthquakes Notes

The Seismograph 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.

Seismogram

Instruments that Monitor Faults Ground movements near a fault are a clue that an earthquake might happen. So scientists measure ground movements near faults. They use tiltmeters, creep meters, laser-ranging devices, and GPS satellites.

Instruments that Monitor Faults Tiltmeters show how much the ground is tilting, or tipping. A tiltmeter works like a carpenter’s level. When the ground tilts, water inside a glass bulb shows how much tilting there is.

Instruments that Monitor Faults Creep meters show how far the sides of a fault have moved in opposite directions. A creep meter uses a wire stretched across a fault. The wire gets longer when the two sides move apart.

Instruments that Monitor Faults Laser-ranging devices use a laser beam to detect horizontal fault mov’t. The device times a laser beam as it travels to a reflector and back. Thus, the device can detect any change in distance to the reflector.

Instruments that Monitor Faults To use the Global Positioning System, scientists put high-tech markers along both sides of the fault. GPS satellites detect any tiny mov’t of the markers in any direction.

Using Seismographic Data When seismic waves reach a fault, they bounce off it, like a ball bouncing off of a wall. Seismographs record the waves that bounce back. Scientists can use the seismographic data to find the fault. This is very similar to biological echolocation as seen in specific species of bats, whales, and dolphins.

Using Seismographic Data Seismographic data can also be used to learn how easily rocks move along a fault. At faults where rock do not move easily, stress builds up, and big earthquakes are likely. Friction is one factor that determines how easily a rock will move.

Using Seismographic Data Sometimes stress builds up, with no earthquake. Sometimes, the fault will slip somewhere with less stress, and relieve some of the pent up energy from elsewhere along the fault. Even with many sources of data, earthquake prediction is still hit-and-miss. Some even claim that animal behavior can be used to predict earthquakes.

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