It’s International Women’s Day 2023, so the EGU Seismology Division would like to celebrate the life and work of singular seismic-wave spotter – Inge Lehmann (1888-1993), a Danish seismologist who discovered that the inner core was solid!
In 1936, Lehman published her seminal paper, the pithily titled “P’” (Lehmann, 1936), suggesting that the core wasn’t all liquid, but instead had a solid inner core (which deflected the P waves) and a liquid outer core, overturning the established status-quo. The diagram in Figure 3 shows the shadow zone highlighted in blue, where ray 5 shows the ray path that was reflected by a solid inner core, thus ending up in the assumed shadow zone. After further study, she went on to discover a discontinuity in the upper mantle between 190 and 250 km (Lehmann, 1962), where seismic wave speeds increased dramatically, which was later called the Lehmann Discontinuity after her. As a result of Inge’s work, the Earth’s interior had gained a layered mantle, as well as a solid core.
Lehmann, I. (1936). P’. Bureau Central Seismologique International, Traveaux Scientifiques (A), 14-88.
Herndon, J. M. (2010). Inseparability of science history and discovery. History of Geo-and Space Sciences, 1(1), 25-41.
Lehmann, I. (1962). Recent studies of body waves in the mantle of the Earth. Quarterly Journal of the Royal Astronomical Society, 3, 288.
Details of life story: Rousseau, C. (2013). How Inge Lehmann discovered the inner core of the Earth. The College Mathematics Journal, 44(5), 399-408.
This piece, written by Katinka Tuinstra,
is an expanded and adapted version of a short post included within the
Seismology Division’s Advent Calendar for Christmas 2021 by Matthew Kemp.