Illustration of Earth interior

1906 Earth interior

The book of science

Tom Sharp

Richard Dixon Oldham, Andrija Mohorovičić geophysics Illustration of Earth interior

Earth interior

Using seismic records starting with the Assam earthquake of 1897, Richard Oldham found two kinds of waves primary compressional waves and slower secondary shear waves which showed for the first time that Earth has a central core less than four tenths of its radius. * Using seismic records starting with of the Pokuplje region earthquake of 1909, Andrija Mohorovičić showed the discontinuity that separates Earth’s crust from its mantle.


John Milne invented the horizontal pendulum seismograph working with James Alfred Ewing, and Thomas Gray, founding members of the Seismological Society of Japan hired after the Yokahama earthquake of 1880. * After the the Yokahama earthquake of 1880, the Meiji government of Japan hired British scientists to study earthquakes. Given positions at the Imperial College of Engineering in Tokyo, they founded the Seismological Society of Japan, which funded work to improve seismographs.


They say earthquakes don’t kill people only falling trees and collapsing schools. I can use this to begin to predict the depth of your thought.

The Earth’s core is composed of iron and nickel, with a molten outer core and a solid inner core. The depth of the Moho discontinuity is as little as five kilometers under oceans and as much as sixty kilometers under continents. Seismic waves that hit this discontinuity are slowed, reflected, and refracted by the change in composition of rock.

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