What did scientists learn from the information found on seismographs? how deep the ocean is the structure of the earth's crust the depth and density of earth's layers the elements present in the interior

The correct answer is the depth and density of the Earth's layer.  

An instrument used for measuring seismic or earthquake waves is known as a seismograph. They are held in a very solid alignment, either on a concrete base or on the bedrock. The seismograph itself comprises a frame and a mass, which can move comparatively to it.  

A seismograph records and measures seismic waves, which move through the Earth as a consequence of an earthquake. Thus, it can provide information on the depth and density of the Earth's layers.  

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