Mohorovicic
ACHIEVEMENT(S): Discovered the Mohorovicic discontinuity (boundary between the Earth's crust and mantle)
DATE AND PLACE OF BIRTH: January 23, 1857, Volosko, Croatia, Austrian Empire
DATE/PLACE OF DEATH/AGE AT DEATH: December 18, 1936, Zagreb, Yugoslavia [now Croatia]. Aged 79
DISCIPLINE: Meteorologist/Seismologist
FIELD: Seismology
LANGUAGE: Croatian and other European languages
PARENTS: Names unknown
SIBLINGS: Unknown
SPOUSE: Name unknown
CHILDREN: Stjepan (also a distinguished seismologist)
EDUCATION: Rijeka Grammar School, Croatia; University of Prague
MAJOR WORK: "Das Beben vom 8.X.1909"
LIFE AND TIMES:
In 1875, Mohorovicic entered the University of Prague to study mathematics and physics and attended lectures by Austrian physicist Mach*. Graduating in 1878, Mohorovicic taught in a secondary school for four years before joining the Royal Nautical School at Bakar, near Rijeka, as a teacher of meteorology and oceanography. Meteorology soon became his passion, and in 1887 he helped establish the Meteorological Station at Bakar.
In 1891, he was made a professor at the Main Technical School in Zagreb, and a year later became director of the school's meteorological observatory. He got his doctorate from the University of Zagreb in 1897, and the same year began working there as an unsalaried lecturer, being promoted to reader in 1910.
All through the 1890s, Mohorovicic had pushed to get Croatian meteorological centers out of the control of Budapest, the capital of Austro-Hungary, of which Croatia was a province. In 1900, he got his way and was allowed to establish the Zagreb observatory as the meteorological center for all Croatia and Slavonia. (The observatory is now called the Regional Center for Meteorology and Geodynamics.)
Soon after, he switched his scientific interest to seismology, a relatively new science that had its beginnings in the 1850s with the work of Irish geologist Mallet*.
On Oct. 8, 1909 the Zagreb observatory recorded a minor earthquake in the Kulpa Valley, about 30 miles south of Zagreb. Mohorovicic collected seismographs and other physical material from all the stations in the area, and set about making a thorough systematic study of the tremor.
By the turn of the 20th century, seismologists had discovered that when an earthquake occurs, tiny vibrating rock particles distribute the energy in wave form. These waves, known as "body" waves, radiate in all directions. The primary, or "P" waves, are compressed and cause a bumping, back-and-forth motion. The secondary, or "S" waves, have an up-and-down motion. Mohorovicic noted that there were two distinct pairs of P and S waves. One set moved slowly but directly through the outer part of the earth (the earth's crust) but waves underneath (in the earth's mantle) moved much faster, arriving at seismic detecting stations well before the surface waves.
Mohorovicic correctly concluded that the speed of seismic waves must depend on the density and elasticity of the materials through which they move, and that since waves moved slower through the earth's crust, the earth's crust and the earth's mantle (which extends 1,800 miles to the earth's core) must have different physical and chemical compositions, and that a boundary, or "discontinuity" (though a relatively narrow one) must exist between them.
The boundary separating the crust and the mantle is now called the "Mohorovicic discontinuity." Mohorovicic's initial calculations suggested that the boundary layer was between 30 and 35 miles thick. (Later calculations verified the existence of the discontinuity but reduced Mohorovicic's estimate to about 20 miles thick.)
Often referred to as simply the Moho, this crust-mantle boundary is found all over the world, although it is deeper under major mountain ranges, and only three to six miles deep below ocean floors. Modern instruments have shown that seismic-wave velocity rapidly increases to more than 5 miles per second at this boundary.
Mohorovicic's other scientific achievements include the development of a method for determining the epicenter of earthquakes, and a model for estimating the travel time of seismic waves over distances of up to 10,000 miles.
In his later years, he attempted to develop earthquake-proof buildings and studied ways of improving the mechanics of seismographs. His meteorological research was also notable, and he produced a number of important papers on this subject, including articles on cloud movement, tornadoes, atmospheric temperatures, and precipitation patterns.
In 1898, Mohorovicic was elected to the Yugoslav Academy of Sciences and served as secretary of its mathematics and science section from 1918 to 1922. He continued in active seismological research until 1926.
ASSESSMENT: The Mohorovicic Discontinuity had important implications for seismological research
EXTRA CONNECTIONS: His work related to that of Wegener*
ONELINER A. Mohorovicic, discoverer of the Earth’s ‘Moho discontinuity’
BIBLIOGRAPHY:
EB, DSB
Crawford, Tom, "Andrija Mohorovicic", in Notable Twentieth-Century Scientists, ed. Emily J. McMurray, New York & London: Gale Research Inc., 1995
Verney, Peter, The Earthquake Handbook, New York & London, 1979