Søren Gregersen (1942 - 2023)

On 28 September 2023, Søren Gregersen Dr. Scient. State Seismologist Emeritus, passed away in Hørsholm, Denmark, at the age of 81.

Søren 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, Søren 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, Søren worked with researchers and the US military staff running the base and operating a nuclear reactor for a power supply. In regular letters, Søren's adventures on the Greenland ice sheet were published in Danish newspapers, making him famous throughout Denmark as “Søren the scout”. At University of Copenhagen, Søren studied geophysics and specialized in seismology, earning the master of science degree in 1968. After completing his degree, Søren 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 Søren 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. Søren'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. Søren 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 Søren was appointed senior researcher. In 1997, Søren was appointed State Seismologist and headed the section managing the seismic service. In addition, Søren was appointed affiliate professor at University of Copenhagen. In 2004 the seismic service was transferred to the Geological Survey of Denmark and Greenland, where Søren continued his work as State Seismologist until 15 November 2009, when he retired.

After his retirement Søren enjoyed life with his wife Allis and their grandchildren. Søren 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 Søren 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. Søren 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 Søren'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 Søren was always a great pleasure, especially when Allis jointed Søren at the many conferences. Søren 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