Lugwig Geiger

Ludwig Carl Geiger was a Swiss physicist and seismologist who is known for developing a method to determine earthquake epicenters.

Life

Ludwig Carl Geiger was born in [[Basel[Switzerland]] on 16. September 1882. His father was the pharmacist Dr. Friedrich Geiger and his mother was Elisabeth Caroline Geiger (maiden name Knapp). He went to school in Basel until spring 1902. Then he studied in Basel, Berlin, Heidelberg and Göttingen. His subjects were physics, mathematics, astronomy, and chemistry. His Ph.D. thesis on observational aspects of the Zeeman effect was finished at Göttingen on 12. December 1906. In April 1907 he became assistant of Emil Wiechert at the Institute of Geophysics and started to work on seismology. He married in 1907 and two sons were born in 1908 and 1909. Geiger was Wiechert’s assistant until 30. April 1911, then ‘Voluntärassistent’. From 1911 to 1912 Ludwig Geiger mainly worked on atomic physics doing spectroscopy. His ’Habilitation’ on spectral lines was accepted on 16. November 1912. On 17. April 1913 Geiger went to the Samoan islands to become observer at the Samoa observatory until 31. July 1914. The following day, the World War I started, and Ludwig Geiger could not leave Samoa. He became interested in the Samoan culture and astronomical observations. In March 1915 he left the island and returned to Basel. Since he could not get a position as (geo-)physicist, Geiger completely changed his profession. From now on he worked as manager in the pharmaceutic factory of his brother. Ludwig Geiger died on 26. November 1966 at the age of 84 in Basel.

Geiger was in charge for the annual seismic bulletins at Göttingen from 1907 to 1910. Together with Karl Zoeppritz, Geiger determined the incidence angles of teleseismic phases and calculated the geometry of the ray paths, using Benndorf’s law. They proposed a mantle of the Earth made of stone with a thickness of 1519 km and 1438 km from P- and S-wave observations, respectively. Later, from1909 to 1910 Geiger applied the Herglotz-Wiechert formula and derived a 1D Earth model with a discontinuity at 1521 km and 1429 km depth for P- and S-waves, respectively. In 1910 and 1911 Ludwig Geiger and Beno Gutenberg determined improved Earth models with three discontinuities in the mantle at depths of about 1200, 1700, and 245 km. The most famous contribution by Ludwig Geiger is his method for locating epicentres - the Geiger method. He found a possibility to locate earthquakes with accurate P-arrival times only. Starting from a guessed epicentre, the solution is found by a least-squares inversion. Geiger demonstrated his method at the India earthquake of 4. April 1905. He used data from 5 stations (Taschkent, Schemacha, Tiflis, Irkutsk and Batum) and chose as starting solution the macroseismic epicentre at 76° 24’ E and 32° 18’ N. His estimated epicenter is at 77° 7’ E±26’ and 32° 14’ N ±47’. Besides his seismological work Ludwig Geiger also contributed to atomic physics. His Ph.D. and his ’Habilitation’ theses comprise studies on atomic spectroscopy. On Samoa Geiger conducted also geoelectric, geomagnetic and meteorological observations. The Figure displays the error ellipse (in miles) for the epicentre of the India earthquake as determined by Ludwig Geiger in 1910

External links

• www.example.com

ftp://ftp.norsar.no/pub/outgoing/johannes/hist/goett_1.pdf

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