Mohorovicic, Andrija (1857-1936) (World of Earth Science)
Croatian seismologist and meteorologist
Croatian seismologist and meteorologist, Andrija Mohorovicic was the first one to suggest the existence of a boundary surface separating the crust of the earth from the underlying mantle. This layer, which is 5 mi (8 km) deep under the oceans and about 20 mi (32 km) deep under the continents in average, was later named the Mohorovicic discontinuity. In 1970, a large crater on the far side of the Moon was also named in Mohorovicic's honor.
Mohorovicic was born on in Volosko, now in Croatia. After spending his early school years in Volosko, then Rijeka, he studied physics and mathematics at the Faculty of Philosophy, in Prague. In 1882, he started his nine-year carrier in the Nautical School in Bakar teaching meteorology, and beginning his scientific work. A few years later, in 1887, he founded a meteorological station in Bakar.
In 1891, Mohorovicic transferred to Zagreb, and in 1892, he became the head of the Meteorological Observatory in Zagreb. Here he studied and wrote mainly about clouds, rainstorms, thunderstorms, tornadoes, whirlwinds, hail, and winds, focusing interest on these meteorological phenomena and their scientific interpretation, as well as studying the climate of Zagreb. In 1892, he started astronomical observations of stars. In 1893, he established a network of stations for thunderstorm observations. Still in 1893, he received his doctor of philosophy degree at the Zagreb University. In 1899, he founded hail stations, and the same year he started a research project about harnessing wind energy.
In 1901, Mohorovicic became director of the meteorological service of Croatia and Slovenia. In his meteorological research, he was still interested in the detection of tornadoes and thunderstorm tracking. Mohorovicic's last contribution to meteorology was in 1901, when he published his paper on vertically decreasing atmospheric temperature. After the turn of the twentieth century, Mohorovicic's scientific interest focused exclusively on the problems of seismology.
Mohorovicic gradually extended the activities of the observatory to other fields of geophysics: seismology, geomagnetism and gravitation, although as chief of the observatory, Mohorovicic was still responsible for recording all the meteorological data for Croatia and Slovenia. The earthquake in 1909 in Croatia directed his interest towards the examination of seismic waves, and in 1910, Mohorovicic published his findings. His plot (arrival time versus epicenter distance to recording station) used the data from 29 stations within 1,491 mi (2,400 km) of the epicenter. He concluded that at around 31 mi (50 km), there must be an abrupt change in the material in the interior of the earth, because he observed an abrupt change in the velocity of the earthquake waves. Although this conclusion was not accepted immediately, a few years later, in 1915, other researchers confirmed it. This discontinuity region under all the continents and oceans is today called the Mohorovicic discontinuity, or in short, the Moho. Although others later refined the study of crust and upper mantle with the application of new methods, Andrija Mohorovicic was clearly a pioneer of this area.
Mohorovicic also published a paper in 1909 on the effect of earthquakes on buildings that described periods of oscillation, which was considered by his contemporaries to be ahead of the times not only in his own country, but worldwide. In 1910, he became an associate university professor. From 1893 to 1917, he taught subjects in the fields of geophysics and astronomy at the Faculty of Philosophy in Zagreb. In 1893, Mohorovicic first became a corresponding member, then in 1898, a full member of the Academy of Sciences and Arts in Zagreb. Although at the end of 1921 he retired, he worked actively until the late 1920s. He died in 1936, and he is buried in Zagreb.
Because of his extensive work studying epicenters, seismographs, and travel-time curves, much of our knowledge of how earthquakes occur, as well as the current models of the earth's structure can be traced back to the work of Andrija Mohorovicic. Among his other achievements, Mohorovicic also found a procedure for identifying the unique location of earthquake epicenters and formulated an analytical expression for the increase of elastic wave velocity with depth, which was later named Mohorovicic's law. Mohorovicic's thoughts and ideas were original, and he focused his interest in more than one area: the effects of earthquakes on buildings, harnessing the energy of the bora, models of the earth, locating earthquake epicenters, seismographs, and many other subjects also in meteorology. Andrija Mohorovicic was an outstanding scientist and researcher, and his scientific work in the field of seismology rightfully gave him world recognition, making him one of the founders of modern seismology.
See also Earth, interior structure