Who was Inge Lehmann?

Inge Lehmann (1888–1993) was a Danish seismologist celebrated for discovering the Earth's inner core in 1936 through seismic wave data analysis. This led to the identification of the Lehmann discontinuity between the Earth’s inner and outer core, approximately 5,100 km deep. Lehmann also identified another discontinuity in the upper mantle, around 200 km beneath the surface. Besides her groundbreaking discoveries, she cofounded the Danish Geophysical Society in 1936. Her contributions to geophysics were recognized with the William Bowie Medal in 1971, and the Seismological Society of America's Medal in 1977. The American Geophysical Union established the Inge Lehmann Medal in 1995 to honor researchers who significantly advanced the understanding of Earth's mantle and core.

What is a seismologist?

A seismologist is a scientist who studies earthquakes and the propagation of seismic waves within the Earth. Seismologists work to determine subsurface faults and other structures, assess seismic hazards, and predict ground motions in future earthquakes. Inge Lehmann (1888–1993) was a Danish seismologist known for discovering the Earth's inner core in 1936 using seismic wave data. Lehmann examined seismograph data collected after an earthquake in New Zealand and noticed seismic waves with higher amplitudes than expected, leading her to posit a three-shelled model of Earth's interior. There are two boundary regions named after Lehmann. One is between Earth’s inner and outer core at roughly 5,100 km, and the other is approximately 200 km beneath Earth’s surface in the upper mantle.

What important discovery did Inge Lehmann make about the Earth’s inner core?

Inge Lehmann, a Danish seismologist, discovered the Earth's inner core in 1936 through her analysis of seismic wave data. By examining seismograph records from a New Zealand earthquake in 1929, Lehmann noticed that certain seismic waves were "bent" and had higher amplitudes than expected in Russian cities. This led her to propose a three-shelled model of the Earth's interior, consisting of the mantle, outer core, and a solid inner core. Her model suggested that seismic waves travel at different velocities through each shell. The boundary between the inner and outer core is now known as the Lehmann discontinuity.

How did Inge Lehmann use earthquake data in her research?

Inge Lehmann used earthquake data to make her discovery of the Earth's inner core in 1936. After noticing that seismographs in Russian cities recorded seismic waves with higher amplitudes than expected after an earthquake in New Zealand in 1929, Lehmann analyzed seismograph data and discovered that some waves appeared to be "bent". At the time, it was known that the Earth’s core deflected secondary (S) waves and some primary (P) waves. Lehmann published a paper in 1936 that proposed a three-shelled model of the Earth's interior, which included the mantle, outer core, and inner core. Her model suggested that seismic waves travel through each shell at different but constant velocities.

Why was Inge Lehmann’s work important in understanding Earth’s structure?

Inge Lehmann, a Danish seismologist, significantly contributed to understanding Earth's structure through her discovery of the inner core in 1936. By analyzing seismic wave data, Lehmann found that some waves were bent, leading her to propose a three-shelled model of Earth's interior: the mantle, outer core, and inner core. Her work also led to the discovery of the Lehmann discontinuity , the boundary between the inner and outer core, located approximately 3,200 miles beneath Earth's surface.

Inge Lehmann

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Cross-sectional diagram of Earth showing how S-waves and P-waves from an earthquake travel through the planet's layers, with S-waves stopping at the liquid outer core and P-waves bending as they pass through the solid inner core, creating shadow zones.

Quick Facts

Born:: May 13, 1888, Copenhagen, Denmark

Died:: February 21, 1993, Copenhagen (aged 104)

Subjects Of Study:: Earth’s core; seismic wave

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Inge Lehmann

Danish seismologist

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Top Questions

Who was Inge Lehmann?
Inge Lehmann (1888–1993) was a Danish seismologist celebrated for discovering the Earth's inner core in 1936 through seismic wave data analysis. This led to the identification of the Lehmann discontinuity between the Earth’s inner and outer core, approximately 5,100 km deep.

Lehmann also identified another discontinuity in the upper mantle, around 200 km beneath the surface. Besides her groundbreaking discoveries, she cofounded the Danish Geophysical Society in 1936. Her contributions to geophysics were recognized with the William Bowie Medal in 1971, and the Seismological Society of America's Medal in 1977. The American Geophysical Union established the Inge Lehmann Medal in 1995 to honor researchers who significantly advanced the understanding of Earth's mantle and core.
1 Britannica Source
1. Inge Lehmann
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What is a seismologist?
A seismologist is a scientist who studies earthquakes and the propagation of seismic waves within the Earth. Seismologists work to determine subsurface faults and other structures, assess seismic hazards, and predict ground motions in future earthquakes.

Inge Lehmann (1888–1993) was a Danish seismologist known for discovering the Earth's inner core in 1936 using seismic wave data. Lehmann examined seismograph data collected after an earthquake in New Zealand and noticed seismic waves with higher amplitudes than expected, leading her to posit a three-shelled model of Earth's interior. There are two boundary regions named after Lehmann. One is between Earth’s inner and outer core at roughly 5,100 km, and the other is approximately 200 km beneath Earth’s surface in the upper mantle.
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What important discovery did Inge Lehmann make about the Earth’s inner core?
Inge Lehmann, a Danish seismologist, discovered the Earth's inner core in 1936 through her analysis of seismic wave data. By examining seismograph records from a New Zealand earthquake in 1929, Lehmann noticed that certain seismic waves were "bent" and had higher amplitudes than expected in Russian cities.

This led her to propose a three-shelled model of the Earth's interior, consisting of the mantle, outer core, and a solid inner core. Her model suggested that seismic waves travel at different velocities through each shell. The boundary between the inner and outer core is now known as the Lehmann discontinuity.
3 Britannica Sources
Created from Britannica articles using AI. AI can make mistakes, so verify using Britannica articles.
How did Inge Lehmann use earthquake data in her research?
Inge Lehmann used earthquake data to make her discovery of the Earth's inner core in 1936. After noticing that seismographs in Russian cities recorded seismic waves with higher amplitudes than expected after an earthquake in New Zealand in 1929, Lehmann analyzed seismograph data and discovered that some waves appeared to be "bent".

At the time, it was known that the Earth’s core deflected secondary (S) waves and some primary (P) waves. Lehmann published a paper in 1936 that proposed a three-shelled model of the Earth's interior, which included the mantle, outer core, and inner core. Her model suggested that seismic waves travel through each shell at different but constant velocities.
1 Britannica Source
1. Inge Lehmann
Created from Britannica articles using AI. AI can make mistakes, so verify using Britannica articles.
Why was Inge Lehmann’s work important in understanding Earth’s structure?
Inge Lehmann, a Danish seismologist, significantly contributed to understanding Earth's structure through her discovery of the inner core in 1936. By analyzing seismic wave data, Lehmann found that some waves were bent, leading her to propose a three-shelled model of Earth's interior: the mantle, outer core, and inner core. Her work also led to the discovery of the Lehmann discontinuity, the boundary between the inner and outer core, located approximately 3,200 miles beneath Earth's surface.
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1. Inge Lehmann
2. Earth: The interior of Earth
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Inge Lehmann (born May 13, 1888, Copenhagen, Denmark—died February 21, 1993, Copenhagen) was a Danish seismologist best known for her discovery of the inner core of Earth in 1936 by using seismic wave data. Two boundary regions, or discontinuities, are named for her: one Lehmann discontinuity occurs between Earth’s inner and outer core at a depth of roughly 5,100 km (about 3,200 miles), and the other occurs at a depth of approximately 200 km (about 120 miles) beneath Earth’s surface in the upper mantle.

Early life

Inge Lehmann was born to Alfred Lehmann, a psychology professor, and Ida Tørsleff. Growing up in Copenhagen, she attended a high school that treated girls and boys equally—a progressive idea at the time. In 1907 she began her study of mathematics at the University of Copenhagen, intending to obtain a candidata magisterii (cand.mag.; comparable to a master’s degree). From the autumn of 1910 to December 1911, Lehmann attended Newnham College, Cambridge, but fatigue and overwork forced her return to Copenhagen.

Lehmann did not attend school between 1911 and 1918, instead serving as an actuarial assistant. She returned to the University of Copenhagen in 1918 and graduated with a cand.mag. in mathematics in 1920. She continued studying mathematics at the University of Hamburg during the fall of 1922, before taking another position as an actuarial assistant in 1923, this time working with a professor in the actuarial science department at the University of Copenhagen. In 1925 she became an assistant to the head of the Royal Danish Geodetic Institute, and part of her work involved setting up Denmark’s first seismic stations near Copenhagen, as well as in Ivigtut and Scoresbysund (now Ittoqqortoomiit), Greenland. Because of her growing interest in that topic, she again enrolled in the University of Copenhagen and studied seismology during the summer of 1927, later graduating with a magister scientiarum (master of science) in 1928. That same year Lehmann was appointed as the state geodesist and was made the head of the Seismological Department of the Royal Danish Geodetic Institute. She held the latter post until her retirement in 1953.

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Discoveries

earthquake: P waves and S wavesP and S waves travel through the planet Earth after an earthquake. Scientists studying the waves produced by earthquakes learned that Earth's core has separate liquid and solid layers. S waves do not travel through liquid, but P waves do. A simplified diagram shows the S waves on the left and the P waves on the right, but waves of both types would actually radiate in all directions.

The bulk of Lehmann’s work at the Seismological Department involved managing the seismological stations both in Denmark and in Greenland, as well as collecting seismograph information and creating the bulletins associated with the stations. She became interested in determining the location of earthquake epicentres more accurately from the data her seismographs provided. She did so by correlating the primary seismic wave forms collected.. She was also interested in calculating the travel times of various types of seismic waves through the planet.

In 1929, while examining seismograph data collected after a large earthquake in New Zealand, Lehmann noticed that seismographs stationed in the Russian cities of Swerdlowsk (Yekaterinburg) and Irkutsk collected seismic waves with amplitudes that were higher than she had expected. She also discovered that some waves traveling away from the earthquake’s focus appeared to have been “bent.” It was known at the time that Earth’s core deflected secondary (S) waves and some primary (P) waves—thereby creating shadow zones behind the core—as those waves traveled outward from an earthquake’s focus to its antipode on the other side of the planet. In 1936, Lehmann published her findings in a paper that posited a three-shelled model of Earth’s interior (which was made up of the mantle, outer core, and inner core), with seismic waves traveling through each shell at different but constant velocities. The model included Earth’s core but also postulated the existence of an inner core. It was not until 1970 that advances in seismographs provided unequivocal evidence of the inner core’s existence. The boundary between the inner and outer core, which occurs at a depth of roughly 5,100 km (about 3,200 miles), is known as the Lehmann discontinuity.

Lehmann is also known for researching Earth’s mantle. Working with American seismologist Beno Gutenberg in 1954, she noticed the existence of a region in Earth’s upper mantle in which seismic waves travel faster. That region, which spans perhaps 50 km (about 31 miles) and is also known as the Lehmann discontinuity, occurs about 200 km (120 miles) below Earth’s surface.

Awards and accolades

In addition to her discoveries, Lehmann cofounded the Danish Geophysical Society (1936) and chaired the organization in 1941 and 1944. She was awarded the William Bowie Medal of the American Geophysical Union in 1971 for her contributions in the field of geophysics and received the Medal of the Seismological Society of America in 1977. The American Geophysical Union created the Inge Lehmann Medal in her honour in 1995, and, starting in 1997, it was awarded to researchers displaying “outstanding contributions to the understanding of the structure, composition, and dynamics of the Earth’s mantle and core.”

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