Mathematics and seismology
Lehmann studied mathematics in Copenhagen and Cambridge before investigating how earthquake energy travels through the Earth. In 1925 she became Niels E. Nørlund’s assistant at Denmark’s Gradmålingen. Renamed the Geodetic Institute in 1928, it appointed her state geodesist that year, responsible for stations and records in Denmark and Greenland. She retired in 1953.
Proposing an inner core
While studying the 1929 New Zealand earthquake, she found seismic arrivals in locations that existing models did not readily explain. Her 1936 paper P′ used P-wave data to propose an inner region with higher wave velocity, an important step in distinguishing the inner and outer core.