Axel Plešingr (1933 - 2024)

On Easter Monday, 1 April 2024, after a short illness, our colleague from the Geophysical Institute of the Czech Academy of Sciences, Axel Plešingr (also Plešinger), passed away at the age of ninety (90). Axel was one of the founders of European and, without exaggeration, world broadband seismometry.

What path did Axel Plešingr, born 14 July 1933, take to become an expert in broadband seismometry in Europe and the world? Far from a direct path, young Axel specialized in electronics and joined the Geophysical Institute. He was attracted to the institute by an ambitious space study project in the Department of Ionospheric Research, but soon descended from the heights of the ionosphere down below the Earth’s surface to fundamentally change the way seismologists listen to the Earth's pulses. He replaced the by-then widespread and traditionally accepted recordings of seismic motions using narrow-frequency passes with broadband-frequency recordings. Axel built a broadband system, not only at the observatory of the Geophysical Institute, near Kašperské Hory, but also in Książ, Silesia, Poland. In addition to establishing a databank of broadband recordings from the two European sites, Axel designed studies related to the structure of the crust in central Europe based on the dispersion of long- period, surface waves. His broadband system was unique at the time and inspired worldwide seismologists. Today, broadband registration is the standard in seismology, and the map of Europe and the world is dotted by such stations. Axel’s old records from Kašperské Hory and Książ provide invaluable insight into world earthquake recordings that occurred in the days of broadband prehistory.

Axel Plešingr was not just a world-renowned expert in seismometry. Due to his specialty in seismic wave recording, Axel became a seismologist par excellence. His perfect understanding of seismic data, and his ability to accurately distinguish between natural signal and instrument artifacts on seismograms, led to fundamental studies: on the time functions of regional earthquakes, on the possibilities of studying lithospheric anisotropy, and on the possibilities of automatic type analyses for distinguishing between natural earthquakes and artificial seismic phenomena. As a recognized expert in seismometry, Axel helped to introduce modern methods of data recording and processing in many places around the world. His teaching abilities and his role as an expert in various seismological schools and courses, organized by scientific associations such as the European Seismological Commission or the International Union of Geodesy and Geophysics, cannot be overlooked.

In his scientific commitment, Axel Plešingr was rigorous and unrelenting in professional matters, but in his heart, he was always kind and willing to help. He helped others with his peculiar humor, and all of us who were in contact with him at the Geophysical Institute adored him for his spirit. In our memories, he remains with us.

Ivan Pšenčík and Jan Šílený, Czech Academy of Sciences