Recording Earthquakes

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Seismogram

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The record made by a seismograph; the paper on which earthquake waves are recorded.

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Seismograph

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An instrument that detects, records, and measures the vibrations produced by an earthquake.

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Aftershock

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An earthquake wave that follows the main shock of an earthquake along the same fault.

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S-P Interval (Lag time)

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The time between the arrival of P-waves and S-waves at a location where an earthquake occurs or seismic waves are being monitored.

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Epicenter

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The point on the Earth's surface directly above the hypocenter (focus) of an earthquake.

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Tectonic Plate

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A rigid layer of Earth's crust that drifts slowly.

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Plate Boundary

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A place where pieces of the broken lithosphere (crust and upper mantle) meet. There are three types: convergent, divergent, and transform.

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Magnitude

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A measure of the total amount of energy released at the hypocenter (focus) of an earthquake.

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Intensity

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A measure of the damage caused by an earthquake, determined by its effects on people, structures, and nature.

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Focus / hypocenter

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The location in the crust where the rupture of an earthquake begins and energy is released.