Measuring Earthquakes - 12 of 19

Measuring Earthquakes FAQs - 19 Found

What are seismograms? How do you read them?

Seismograms are the recordings of earthquake shaking. Each seismograph records the shaking of the ground at the location of that instrument. The recordings have been done in different ways over the years, from photographic records and paper records, to currently digital records. The paper records were typically long sheets of paper wrapped around drums that slowly rotated, recording the ground movements. These were called "helicorders".  Even now, many years after digital records were first possible, helicorders are used in the public areas of educational institutions as a way to display seismograms to the public.  "Electronic helicorders" or "webicorders" are even used on websites.

Seismograms are used to, among many other applications, calculate the location and magnitude of an earthquake. They show how the ground moves with the passage of time at a single location. On a seismogram, the HORIZONTAL axis = time (measured in seconds) and the VERTICAL axis= ground displacement (usually measured in millimeters). When there is NO EQ reading there is just a straight line except for small wiggles caused by local disturbance or "noise" and the time markers.

Before there were digital seismograms, scientists would use rulers to measure parts of the seismogram to make various calculations.  The current digital seismograms provide much more accurate measurements and thus more accurate results.

Learn More: "An Illustrated Guide to Reading a Seismogram" video
(In this video, the "real data" refers to the digital data.)

Tags: Seismology, Liquefaction, Tsunamis, Earthquakes, Faults, Tectonics, Magnitude, Prediction