Richard Dixon Oldham (1858-1936)
From The Cambridge Dictionary of Scientists
Oldham was educated at the Royal School of Mines, in 1879 joining the Geological Survey of India (of which his father was director). Upon retirement in 1903 he became director of the Indian Museum in Calcutta. Following the violent Assam earthquake of 1897, Oldham was able clearly to distinguish in the seismograph record for the first time between the P (primary, or compressional) and S (secondary, or shear) waves (predicted theoretically by Poisson) and the tertiary (surface) waves.