What are seismographs?
Seismographs are instruments used to record the motion of the ground during an earthquake–installed in the ground throughout the world and operating as a seismographic network; 1st developed ~1890. • Q: What are seismograms? A: The records (paper copy) produced by seismographs used to calculate the location and magnitude of an earthquake. Shows how the ground moves with the passage of time. SEISMO How do you read seismograms? The HORIZONTAL axis = time (measured in seconds); VERTICAL axis= ground displacement (usually measured in millimeters) When there is NO earthquake reading = straight line except for small wiggles caused by local disturbance or “noise.” • Q: What is a seismometer? A: An internal part of the seismograph which may be a pendulum or a mass mounted on a spring. • Q: How is the movement of the seismometer converted into a seismogram? A: There are several ways: • a pen drawing an ink line on paper revolving on a drum; • a light beam making a trace on a moving photographi
