Gilbert was among the first to recognize that the free oscillations of the Earth ( so-called bell-ringing modes ) could be measured immediately following large earthquakes , and could be used to produce structural models of the inner earth . In collaboration with Adam Dziewonski , he applied these ideas first to seismic records from the 1964 Alaska earthquake and then to records from the 1970 Colombia earthquake . In this context he and Backus developed robust methods for inverting seismic data
1964 Alaska earthquake
1964 Alaska earthquake
James Freeman Gilbert