The Seismograph • The Seismograph is a heavy weight attached to a frame by a spring or wire. A pen connected to the weight rests on its point on a drum that can rotate.
How does seismographs work? • 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.
Measuring Seismic Waves • All seismographs make use of a basic principle of physics: whether it is moving or at rest, every object resists any change to its motion. A seismograph’s heavy weight resists motion during a quake. But the rest of the seismograph is anchored to the ground and vibrates when seismic waves arrive.
Seismogram • Look at C5S2 Notes for definition
Reading Seismograms • P waves travel fastest • S waves arrive shortly after P waves • Surface waves produce the largest disturbance on the seismogram.
How do Geologists Monitor Faults? • To monitor faults, geologists have developed instruments to measure changes in elevation, tilting of the land surface, and ground movement along faults.
Tilt meter • A tilt meter measures tilt or raising of the ground. • It consists of two bulbs that are filled with liquid and connected by a hollow stem. It works like a level.
Creep Meter • Uses a wire stretched across a fault to measure horizontal movement of the ground. • One side is anchored to a post and the other side is attached to a weight that can slide if the fault moves.
Laser Ranging Device • Uses a laser beam to detect horizontal fault movement. The device times a laser beam as it travels to a reflector and back.
GPS • Scientists can monitor changes in elevation as well as horizontal movements along faults using a network on Earth’s Orbiting Satellites GPS (global positioning System)
How are seismographic data used? • Seismographs and fault-monitoring devices provide data used to map faults and detect changes along faults. Geologists are also trying to use data to develop a method of predicting earthquakes.
Mapping Faults • Since most faults are hidden by a thick layer of rock and soil. Geologists had to figure a way to map faults. They discovered that when seismic waves hit a fault, the waves are reflected off the fault. Seismographs can detect these reflected seismic waves. Geologists use this information to map the fault.
Monitoring changes along faults • Geologists study the types of movement that occur along faults. Along parts of some faults, the rocks on both sides are smooth and slide by each other without much sticking. • Other faults have large amounts of sticking due to rough and jagged edges, this sticking creates friction.
Friction • Is a force that opposes the motion of one surface as it moves across another surface. Friction exists because surfaces are not perfectly smooth.
The More Friction, the Greater the Earthquake!Earthquakes are not accurately predicted at this time, but if you could figure out how, you can become rich.