| 21. | The Richter scale is a measure of ground motion as recorded on seismographs.
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| 22. | Active volcanoes in developed countries can have several observatories and dozens of seismographs.
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| 23. | The output of a digital seismograph can be simply input to a computer.
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| 24. | Therefore, most professional seismographs are sealed in rigid gas-tight enclosures.
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| 25. | Each rotation of the seismograph drum is thirty minutes.
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| 26. | The high and low bounds are representative noise limits for seismographs deployed worldwide.
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| 27. | The instruments include seismographs that monitor ground vibrations.
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| 28. | Later in the week, checking seismograph records, it turned out I had.
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| 29. | Not everyone cared for what the seismograph recorded.
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| 30. | Most of them are too weak to be felt by anything but a seismograph.
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