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USGS Geology in the Parks

Joshua Tree National Park Geology: Hector Mine earthquake seismogram

Recorded near Palmdale, California, October 16, 1999

Hector Mine earthquake seismogram

If you experienced the Mojave desert's most recent earthquake first hand, you know that earthquakes can produce BIG vibrations. These vibrations can be detected by sensitive devices called seismometers. Data from the seismometer is sent to a seismograph where it is recorded.

A pen at the top of the seismograph records a zig-zag line on the moving, paper-covered cylinder whenever an earthquake is detected. Each day the paper record, called a seismogram, is removed and replaced with a new one. Scientists then analyze the earthquake data from the seismogram. Seismographs can help us determine the time, epicenter, focus, and the type of faulting that produced an earthquake as well as estimate how much energy was released.

Most of the time the seismograph pen draws a fairly smooth line, telling us that no earthquakes have occurred within range of our seismograph's sensitivity. Most of the horizontal lines recorded on the seismogram above are smooth, with regular 'blips' that scientists use to help keep track of the time of day. It doesn't take an expert to see the earthquake record on this seismogram!

Click here to see entire seismogram (large file: 189 MB)

Click here learn about how seismograms are made at Sunset Crater Volcano National Monument.

Click here load high resolution, full-size gif to print. (large filel: 212 MB)

| U.S. Geological Survey Pasadena Office of Earthquake Information |
| Joshua Tree earthquake home | Joshua Tree National Park home |

 

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