Inge Lehmann

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Inge Lehmann
Inge Lehmann 1932.jpg
Latest company Geodetic Institute
BSc physical science, mathematics
BSc university University of Copenhagen, University of Cambridge

Inge Lehmann (May 13, 1888 – February 21, 1993) was a Danish seismologist and geophysicist. In 1936, she discovered that the Earth has a solid inner core inside a molten outer core. Before that, scientists believed Earth's core to be a single molten sphere. However, seismologists had been unable to explain careful measurements of seismic waves from earthquakes, which were inconsistent with the Earth having a single molten core. Lehmann analysed the seismic wave measurements, and she concluded that Earth must have a solid inner inside a molten outer core to produce seismic waves that matched the measurements. Other seismologists tested and then accepted Lehmann's explanation. [1][2][3]

Career

A modern understanding of the Lehmann discontinuity: velocity of seismic S-waves in the Earth near the surface in three tectonic provinces: TNA = Tectonic North America SNA = Shield North America and ATL = North Atlantic.[4]

In 1925 Lehmann became an assistant to the geodesy Niels Erik Nørlund, who assigned her the task of setting up seismological observatories in Denmark and Greenland. Based on her studies in seismology, in 1928 she earned the magister scientiarum degree (equivalent to an MA) in geodesy and accepted a position as state geodesist and head of the department of seismology at the Geodetical Institute of Denmark led by Nørlund.[5] Lehmann looked into improving the coordination and analysis of measurements from Europe's seismographic observatories, as well as many other scientific endeavours."Inge Lehmann: Discoverer of the Earth's Inner Core". http://www.amnh.org/explore/resource-collections/earth-inside-and-out/inge-lehmann-discoverer-of-the-earth-s-inner-core/.</ref>

In a paper titled P' (1936),[6] Lehmann was the first to interpret P wave arrivals—which inexplicably appeared in the P wave shadow of the Earth's core—as reflections from an inner core, for example from the strong 1929 Murchison earthquake.[7] 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 when the interpretation was shown correct by computer calculations.[8] Lehmann was significantly hampered in her work and maintaining international contacts during World War II and the German occupation of Denmark. She served as the Chair of the Danish Geophysical Society in 1940 and 1944 respectively.

In 1952, Lehmann was considered for a professorship in geophysics at Copenhagen University, but was not appointed. In 1953, she retired from her position at the Geodetic Institute. She moved to the US for several years and collaborated with Maurice Ewing and Frank Press on investigations of Earth's crust and upper mantle. During this work, she discovered another seismic discontinuity, which lies at depths between 190 and 250 km and was named for her, the Lehmann discontinuity. Francis Birch noted that the "Lehmann discontinuity was discovered through exacting scrutiny of seismic records by a master of a black art for which no amount of computerization is likely to be a complete substitute."[8]


References

  1. "Lehmann, Inge". Complete Dictionary of Scientific Biography. Detroit, MI: Charles Scribner's Sons. 2008. http://www.encyclopedia.com/topic/Inge_Lehmann.aspx. Retrieved 15 October 2013.
  2. "Lehmann; Inge (1888–1993)". The Royal Society: Past Fellows. https://collections.royalsociety.org/DServe.exe?dsqIni=Dserve.ini&dsqApp=Archive&dsqDb=Persons&dsqSearch=Code==%27NA5258%27&dsqCmd=Show.tcl. Retrieved 24 September 2013.
  3. Bolt, Bruce A. (January 1994). "Inge Lehmann". Physics Today 47 (1): 61. doi:10.1063/1.2808386.
  4. Figure patterned after Don L Anderson (2007). New Theory of the Earth (2nd ed.). Cambridge University Press. p. 102, Figure 8.6. ISBN 0-521-84959-4. https://books.google.com/books?id=KB3KsIPa94sC&pg=PA102.; Original figure attributed to Grand and Helmberger (1984)
  5. Maiken, Lolck (2008). ""Lehmann, Inge." Complete Dictionary of Scientific Biography". Vol. 22: Gale. pp. 232–236. http://go.galegroup.com.rp.nla.gov.au/ps/i.do?id=GALE%7CCX2830905851&v=2.1&u=nla&it=r&p=GVRL&sw=w&asid=7c6d1a9b82c004b488f179acdeb4ab08. Retrieved 22 May 2015.
  6. Lehmann, I. (1936): P’, Publications du Bureau Central Seismologique International, Série A, Travaux Scientifique, 14, 87–115.
  7. Bolt, Bruce A. (1987). "50 years of studies on the inner core". EOS 68 (6): 73,80–81.
  8. 8.0 8.1 Dahlmann, Jan (23 January 2005). "Inge Lehmann og Jordens kerne" (in Danish). http://ing.dk/artikel/inge-lehmann-og-jordens-kerne-78611. Retrieved 14 May 2015.

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