Richard Dixon Oldham, British geologist who makes the first clear identification of the separate arrivals of P-waves, S-waves and surface waves on seismograms and the first clear evidence that the Earth has a central core, is born in Dublin on July 31, 1858.
In 1879 Oldham becomes an assistant-superintendent with the Geological Survey of India (GSI), working in the Himalayas. He writes about 40 publications for the Survey on geological subjects including hot springs, the geology of the Son Valley and the structure of the Himalayas and the Indo-Gangetic plain. His most famous work is in seismology. His report on the 1897 Assam earthquake goes far beyond reports of previous earthquakes. It includes a description of the Chedrang fault, with uplift up to 35 feet and reported accelerations of the ground that have exceeded the Earth’s gravitational acceleration. His most important contribution to seismology is the first clear identification of the separate arrivals of P-waves, S-waves and surface waves on seismograms. Since these observations agree with theory for elastic waves, they show that the Earth can be treated as elastic in studies of seismic waves.
In 1903, Oldham resigns from the GSI due to ill health and returns to the United Kingdom, living in Kew and various parts of Wales. In 1906 he writes a paper analyzing seismic arrival times of various recorded earthquakes. He concludes that the earth has a core and estimates its radius to be less than 0.4 times the radius of the Earth.
Richard Dixon Oldham dies at Llandrindod Wells in Wales on July 15, 1936.