Mohorovičić, Andrija (1857–1936)

Croatian seismologist and meteorologist who discovered the Mohorovičić discontinuity, the boundary between the earth's crust and the mantle.

In 1909 after a strong earthquake occurred in the Kulpa Valley south of Zagreb, Mohovoricic discovered two distinct sets of P- and S-waves (types of seismic wave) – one set arriving earlier than the other. He deduced that one set of waves was slower than the other because it had travelled through denser material. Mohorovičić proposed that the earth's surface consists of an outer layer of rocky material approximately 30 km/19 mi thick, which overlies a denser mantle. Later research has shown that the boundary between these two layers, the ‘Moho’, lies at a depth of 5–10 km/3–6 mi beneath the ocean crust and approximately 35 km/21 mi beneath the crust of the continents. Seismic waves travel nearly 20% slower below the Moho than above and it is regarded as the bottom of the earth's crust.

Born in Volosko, Croatia, Mohorovičić studied mathematics and physics at Prague University. After seven years as a school teacher, he became a professor at the Zagreb Technical School and later Zagreb University. In 1892 he became director of the Meteorological Station in Zagreb, which later became the Royal Regional Centre for Meteorology and Geodynamics, establishing a seismological observatory there in 1901.

The Royal Regional Center for Meteorology and Geodynamics was renamed the Geophysical Institute in 1921. Mohorovičić continued seismological research there until 1926.