William Lowrie is Professor Emeritus of Geophysics at the Institute of Geophysics at Eidgenössische Technische Hochschule Zürich, Switzerland, where he taught geophysics and carried out research in rock magnetism and paleomagnetism. He graduated from the University of Edinburgh in 1960 with first class honors in physics, before completing a masters degree in geophysics at the University of Toronto and a doctorate at the University of Pittsburgh. He has been President of the European Union of Geosciences (1987-9) and Section President and Council member of the American Geophysical Union (2000-2). He is a Fellow of AGU and a Member of the Academia Europaea. Andreas Fichtner is Professor of Geophysics at Eidgenössische Technische Hochschule Zürich. He received his Ph.D. in 2010 from the University of Munich. His principal research interests include the development and application of methods for full seismic waveform inversion, resolution analysis in tomography, earthquake source inversion, seismic interferometry, and inverse theory. For his work, he received the Keiiti Aki Award from the American Geophysical Union, the Early Career Scientist Award from the International Union of Geodesy and Geophysics, and the Hoffmann Prize from the Bavarian Academy of Sciences. He is a former Fulbright scholar and a current member of the Young Academy of Europe.