S?ren Gregersen (1942 - 2023)

On 28 September 2023, S?ren Gregersen Dr. Scient. State Seismologist Emeritus, passed away in H?rsholm, Denmark, at the age of 81.

S?ren Gregersen was born on 27 April 1942 and from a young age had a strong interest in science. At that time growing up in Denmark, science was dominated by Niels Bohr, and major advances in physics were being made. In October 1960, at the age of 18, S?ren was selected along with an American scout, to live for six months at the Camp Century base, where drilling into the Greenland ice sheet was underway. During his time at the base, S?ren worked with researchers and the US military staff running the base and operating a nuclear reactor for a power supply. In regular letters, S?ren's adventures on the Greenland ice sheet were published in Danish newspapers, making him famous throughout Denmark as “S?ren the scout”. At University of Copenhagen, S?ren studied geophysics and specialized in seismology, earning the master of science degree in 1968. After completing his degree, S?ren was employed as a geodesy assistant at the Danish Geodetic Institute, where the seismic service at that time was hosted and that operated and reported on data from seismographs in Denmark and Greenland since 1927. In 1970 S?ren went to the Lamont-Doherty Geological Observatory at Columbia University in New York, U.S.A., where he graduated with a Ph.D. in seismology in 1974. His thesis was on the amplitudes of horizontally refracted Love waves. As a researcher, he returned to the Danish Geodetic Institute and continued his work in seismology focusing on earthquakes in Denmark and Greenland, Lg wave propagation and Lg wave tomography. S?ren's studies on Lg waves constituted a major part of his Dr. scient thesis which he successfully defended at University of Copenhagen on 6 December 1985. S?ren presented his research on many journeys around the world and often was provided with gifts for Inge Lehmann, which he presented to her during coffee at her apartment in Copenhagen.

In 1994 the seismic service was transferred to the National Survey and Cadastre where S?ren was appointed senior researcher. In 1997, S?ren was appointed State Seismologist and headed the section managing the seismic service. In addition, S?ren was appointed affiliate professor at University of Copenhagen. In 2004 the seismic service was transferred to the Geological Survey of Denmark and Greenland, where S?ren continued his work as State Seismologist until 15 November 2009, when he retired.

After his retirement S?ren enjoyed life with his wife Allis and their grandchildren. S?ren also received the Emeritus title at the Geological Survey of Denmark and Greenland, publishing several papers mainly focused on postglacial uplift and earthquakes in Scandinavia.

I first met S?ren in the mid 1990s, where he was a regular visitor at the Institute of Geophysics where I did my studies, and we later became close colleagues at the seismic service. S?ren was always welcoming seismology students as a supervisor, providing lectures, leading study groups and much more. We were many students across Europe that benefited from S?ren's leadership during the Teleseismic Tomography experiment across the Tornqust Zone, in short the TOR project, one of the first large multi-national deployments of broad band and short period digital mobile seismic stations, in Germany, Denmark and Sweden. Traveling with S?ren was always a great pleasure, especially when Allis jointed S?ren at the many conferences. S?ren had an enormous network in the research community from his engagement at the IUGG, the CTBTO, and many other international collaborations. He was always eager to share his network and to bring people together with a contagious kindness, enthusiasm, and optimism.

Peter Voss, 12 October 2023