A German seismologist who emigrated to the USA in the 1930s, in 1913 Gutenberg used seismic data to calculate the diameter of the core. In 1926, he established the existence of the low-velocity layer (see low-velocity zone), noting that seismic waves from foci with depths of 50–250 km took longer to arrive than expected. At the California Institute of Technology he continued his seismic studies in collaboration with C. F. Richter. See also gutenberg discontinuity.