Inge Lehmann ForMemRS (13 May 1888 – 21 February 1993) was a Danish seismologist and geophysicist who is known for her discovery in 1936 of the solid inner core that exists within the molten outer core of the Earth. The seismic discontinuity in the speed of seismic waves at depths between 190 and 250 km is named the Lehmann discontinuity after her. Lehmann is considered to be a pioneer among women and scientists in seismology research.
In 1925, Lehmann was assigned to be the assistant of seismologist Niels Erik Nørlund. She took an interest in his field, and she began studying it on her own. She was chosen as a delegate for Denmark to attend the International Union of Geodesy and Geophysics in 1927—a role she filled another eight times over the next forty years. By 1928, Lehmann obtained a magister scientiarum in seismology, and she was appointed head the Geodætisk Institut‘s seismological department the same year. In this position, she was responsible for overseeing the operation of three seismographic observatories, two of which were in Greenland. She personally operated the one in Copenhagen, producing reports based on its readings. Though it was not part of her job, Lehmann also engaged in research at the facility.
In 1929, Lehmann studied the Murchison earthquake which struck on the South Island of New Zealand. She analyzed the seismic data from the earthquake and noticed that there were waves of significant amplitude recorded in the Russian cities of Sverdlovsk and Irkutsk, both unexpected locations. They were unexpected locations due to the theory that S-waves and some P-waves are deflected by the core creating a shadow area in which waves are not able to pass through. The waves seemed to pass through that area to reach Russia. This led to her discovering that there is a spherical core of solid material at the Earth’s centre.
“We take it that, as before, the Earth consists of a core and a mantle, but that inside the core there is an inner core in which the velocity is larger than in the outer one.”
Lehmann (1936)
Lehmann was the first to interpret P-wave arrivals as reflections from an inner core. She published her findings in a paper titled P′ (1936), The theory she developed was that the Earth consisted of 3 shells: the mantle, outer core and inner core. Lehmann inferred that the core wasn’t homogeneous; rather, there is a smaller core that exists that is surrounded by the outer core. She deduced that waves travel faster in the smaller core, but the waves can be reflected off if it arrived tangentially. Her theory allows for another wave deflection at the extra boundary and this accounts for the direction and location in which the waves emerge. Other leading seismologists of the time, such as Beno Gutenberg, Charles Richter, and Harold Jeffreys, adopted this interpretation within two or three years, but it took until 1971 for the interpretation to be shown correct by computer calculations.
Source: Inge Lehmann – Wikiwand Accessed 12 Apr. 2024.
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