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Using Seismographs, Then and Now
Using Seismographs, Then and Now
The Modern Seismograph
A modern seismograph, also called a seismometer, records the shaking of Earth's surface caused by
seismic waves. A seismogram is the record a seismograph makes. A seismogram shows seismic waves
as jagged up-and- down lines. Scientists compare multiple seismograms in order to pinpoint an
earthquake's epicenter.
Modern seismograph
The First Seismograph
Zhang Heng, a Chinese scientist, invented the first-known seismograph around 132 CE. It didn't look
anything like a modern seismograph. It was shaped like a large vase. The vase had eight dragons around
the outside, each looking downward and holding a ball loosely in its mouth. Below the eight dragons
were open-mouthed frogs. When an earthquake struck, the balls fell into the frogs' mouths below.
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Using Seismographs, Then and Now
Depending on which balls fell, it was possible to estimate the distance and direction to the earthquake's
source.
First-known seismograph
Learning About Our Earth from Seismographs
Scientists can learn a lot from seismographs, beyond just where an earthquake's epicenter. Take the
Danish scientist Inge Lehmann, for example. In her time, around 1900, scientists thought the earth had
just three layers: an outer crust, a solid mantle, and a liquid core. Lehmann studied seismograph records
of earthquakes. She analyzed how seismic waves changed as they traveled through Earth's interior.
Lehmann collected thousands of records organized in boxes-there were no computers back then! She
saw patterns in how seismic waves behaved as they moved through Earth. Lehmann concluded that
Earth's core has two parts: a liquid outer core and a solid inner core. In 1936, she announced her findings
and changed our view of Earth!
ReadWorks.org · © 2016 ReadWorks®, Inc. All rights reserved. This article is based on an original work of the Core Knowledge® Foundation made available through licensing under a Creative Commons
Attribution-NonCommercial-ShareAlike 3.0 Unported License. This does not in any way imply that the Core Knowledge Foundation endorses this work. This article is licensed under a Creative Commons
Attribution-NonCommercial-ShareAlike 3.0 Unported License. https://creativecommons.org/licenses/by-nc-sa/3.0/
Using Seismographs, Then and Now
ReadWorks.org · © 2016 ReadWorks®, Inc. All rights reserved. This article is based on an original work of the Core Knowledge® Foundation made available through licensing under a Creative Commons
Attribution-NonCommercial-ShareAlike 3.0 Unported License. This does not in any way imply that the Core Knowledge Foundation endorses this work. This article is licensed under a Creative Commons
Attribution-NonCommercial-ShareAlike 3.0 Unported License. https://creativecommons.org/licenses/by-nc-sa/3.0/