USA

James Freeman Gilbert

1990 Balzan Prize for Geophysics (Solid Earth)

For his outstanding contribution to our knowledge of the Earth’s deep interior.

Professor James Freeman Gilbert’s (1931 – 2014) contribution to the Physics of the Solid Earth has opened the way to a more exact knowledge of the Earth’s interior.
Strong earthquakes produce free oscillations of the Earth. Since the Mid-Sixties they could be investigated by using very precise gravimeters and long-period seismometers, but the resulting collections of data needed a new analytical method for their interpretation. Together with George BACKUS. James Freeman GILBERT became the pioneer of the so-called “Geophysical Inverse Theory’ (1966/67), now widely used not only in geophysics, but also in other branches of science.
The theory was developed to find the best model of the Earth’s interior fitting the data obtained from observations on the Earth’s surface. This provided a tool for determining the distribution of density and elastic constants in the Earth’s mantle and core.
By analysing deep earthquakes in cooperation with Adam DZIEWONSKI (1975/76), convincing arguments were obtained for the solid nature of the inner core of the Earth.
Based on these successes Professor GILBERT and others proposed and established a global array of precision gravimeters (International Deployment of Accelerators, IDA). This network has continued to grow and has been improved with time. Today it is an outstanding example of international cooperation in science.
Professor GILBERT founded a School in La Jolla, California from where not only outstanding publications but also excellent young seismologists emerged.