The resulting report was presented to the Royal Society as the "Report on the Great Neapolitan Earthquake of 1857". It was a major scientific work and made great use of the then new research tool of photography to record the devastation caused by the earthquake. In 1862, he published the ""Great Neapolitan Earthquake of 1857: The First Principles of Observational Seismology"" in two volumes; he brought forward evidence to show that the depth below the Earth's surface, from where the impulse of the Neapolitan earthquake originated, was about 8–9 geographical miles. One of Mallet's papers was "Volcanic Energy: an Attempt to develop its True Origin and Cosmical Relations", in which he sought to show that volcanic heat may be attributed to the effects of crushing, contortion and other disturbances in the crust of the earth; the disturbances leading to the formation of lines of fracture, more or less vertical, down which water would find its way, and if the temperature generated be sufficient volcanic eruptions of steam or lava would follow. During the Crimean War he designed a mortar of calibre capable of throwing a shell a distance of . The huge mortar was built in sections to allow transport, but was too late to be used in action. An example has been preserved at the Royal Artillery base in Woolwich and one is displayed before the Royal Armouries Fort Nelson near Portsmouth. Mallet was elected Fellow of the Royal Society in 1854, and in 1861 moved to London, where he became a consulting engineer and edited "The Practical Mechanic's Journal". He was awarded the Telford Medal by the Institution of Civil Engineers in 1859, followed by the Cunningham Medal of the Royal Irish Academy for his research into the theory of earthquakes in 1862 and the Wollaston medal of the Geological Society of London in 1877, the Geological Society's highest award. Blind for the last seven years of his life, he died at Stockwell, London, on 5 November 1881 and is buried at West Norwood Cemetery.