Andrija Mohorovičić

Andrija Mohorovičić (1857–1936) was a Croatian geophysicist and seismologist who identified the boundary between Earth’s crust and mantle, now called the Mohorovičić discontinuity.

Mohorovičić discontinuity: The seismic boundary separating Earth’s crust from its mantle, marked by a sharp increase in wave velocity. The boundary he discovered bears his name and remains a defining result of his work.
Seismic refraction: The bending of seismic waves as they cross boundaries between materials with different wave speeds. Refraction at the crust–mantle boundary explains the unexpectedly early arrivals he analyzed.
Kupa Valley earthquake of 1909: A damaging earthquake near Pokupsko, Croatia, on 8 October 1909, whose records Mohorovičić analyzed. Its seismograms supplied the decisive evidence for his crust–mantle boundary.
Croatian Meteorological and Hydrological Service: Croatia’s national service for meteorological, hydrological, and related environmental monitoring. Its institutional history includes the Zagreb observatory Mohorovičić directed.
Seismic wave: A wave of energy that travels through Earth or along its surface, commonly generated by earthquakes. Changes in seismic-wave arrival times exposed the hidden boundary he identified.
Seismogram: A recorded trace of ground motion produced by a seismograph. Arrival times on earthquake records supplied the observations behind his inference.
Zagreb: The capital of Croatia, where Mohorovičić worked and directed the meteorological observatory. His seismological investigations were based at Zagreb’s observatory.
Beno Gutenberg: A German-American seismologist who helped establish the depth of the core–mantle boundary and advanced earthquake science. His later seismic research extended the use of wave behavior to map Earth’s interior.
Earth's crust: Earth’s outermost solid layer, comprising continental and oceanic crust. His discovery established the crust’s lower boundary beneath the mantle.
Seismic velocity: The speed at which a seismic wave travels through a material. The abrupt velocity increase across the interface was the key clue in his analysis.

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