Andrija Mohorovičić

Croatian geologist

• Born: January 23, 1857; Opatija, Croatia
• Died: December 18, 1936; Zagreb, Croatia

Andrija Mohorovičić’s research on the structure and makeup of the Earth’s crust contributed to the rise of seismology, the scientific study of earthquakes, in the twentieth century. The disparate geological region that separates the Earth’s crust and mantle layers is dubbed the “Mohorovičić discontinuity,” or Moho, in his honor.

Primary field: Earth sciences

Specialties: Geology; seismology

Early Life

Andrija Mohorovičić was born in the western Croatian city of Opatija in 1857. His father, a blacksmith by trade, raised him after his mother’s death due to complications in childbirth. Mohorovičić’s academic prowess was evident from a very early age. After completing primary and grammar schooling in Opatija’s Volosko district by the age of fifteen, he was already fluent in English, French, and Italian.

In 1875, Mohorovičić graduated from the University of Prague, having studied mathematics and physics under the venerated Czech Austrian physicist and philosopher Ernst Mach. Well-known for his scientific research on shock waves and supersonic flow, Mach may have had an influence on Mohorovičić’s eventual academic path.

Upon graduation Mohorovičić began a career as a teacher, first as an instructor of grammar school students, then as an instructor of math, physics, and meteorology at the Nautical School in the seaside village of Bakar, Croatia. In Bakar’s coastal location, thunder, lightning, and hail were common occurrences, which further sparked the young teacher’s interest in meteorological studies. In fact, Mohorovičić was a prominent force in the construction of a meteorological research center at the Nautical School, which he utilized for both instructional purposes and his own research. It was also during this time that Mohorovičić met his wife Silvija, with whom he would have four sons.

Mohorovičić’s interest in the natural sciences is evident by the several scientific research papers he penned during his time in Bakar, which concentrated on a number of meteorological topics, including studies on wind movement and cloud direction. Mohorovičić’s papers on clouds, cloud types, and related airflow yielded preliminary observations of what is known today as wave phenomena. His meteorological work in Bakar eventually enabled him to earn a doctoral degree from the University of Zagreb in 1897.

Life’s Work

Mohorovičić moved with his family to the Croatian capital of Zagreb in the early 1890s, where he would stray from his meteorological interests and begin to immerse himself fully in research related to the Earth’s surface. In 1892, he was named the head of the meteorological observatory in Zagreb.

At this point in his career, Mohorovičić’s aptitude as meteorologist preceded him, prompting the editor of Zagreb’s major newspaper, Agramer Zeitung, to plead with him to provide tentative weather forecasts for daily editions. Of Mohorovičić’s several hundred forecasts in 1896, over seventy percent were deemed to be accurate, an impressive degree of precision given the meteorological apparatus available at the time. By the time a new wave of meteorologists had begun to make more precise predictions relating atmospheric circulation and density to temperature and humidity, Mohorovičić was well established as an expert seismologist.

Scholars agree that many factors were involved in Mohorovičić’s eventual departure from meteorological studies, though he left no letters or memoirs describing the exact reasons for his shift in focus. In addition to his frustration with rudimentary equipment and data-tracking devices, the outbreak of World War I had resulted in many of his assistants reporting for military duty. Furthermore, difficulties in communication severely limited the flow of information regarding weather conditions in other regions of Europe.

Mohorovičić would make a contribution to the war effort in 1901. With the help of remaining assistants, he led an analysis of newly unveiled cannon prototypes in the hope of determining which weapon would be the simplest, most effective, and most cost efficient to operate.

Under Mohorovičić’s supervision, the Zagreb Observatory underwent a complete transformation and was redubbed the Royal Regional Center for Meteorology and Geodynamics. Mohorovičić would transform this institute into one of the world’s most important centers for seismological study. His role as director allowed him to expand his research activities into experiments investigating the properties of geomagnetism and the role of gravity in the Earth’s geological composition and behavior in orbit.

By the time of Mohorovičić’s arrival in Zagreb, the major concepts of seismological studies were very much in their infancy. German scientist Ernst von Rebeur-Paschwitz had become the first to capture earthquake vibrations, which he detected on seismic monitoring equipment of his own invention. Having observed seismic activity in Japan, in the spring of 1889 Rebeur-Paschwitz inspired an international seismological observatory alliance. It was in the early 1900s that German seismologist Beno Gutenberg began to observe varying seismic wave velocities at different depths of measurement.

Mohorovičić led a 1909 study in a similar vein. He concentrated on the time sequences of seismic waves between monitoring stations throughout southeastern Europe. Mohorovičić was able to utilize the data to hypothesize that some seismic waves resulting from movement in the Earth’s crust took longer than others to reach monitoring stations, despite emerging from the same seismic event. Mohorovičić hypothesized that the cause of such lapses was a previously undiscovered boundary, or discontinuity, between the Earth’s crust—its mountainous outer shell—and the Earth’s mantle, or denser mineral sublevel. His findings would be published in a 1910 paper, in which he proposed his interpretation of seismic wave velocities and a discontinuity between the planet’s top geographical surfaces as the standard for all future research. Mohorovičić’s discontinuity theory came to represent a massive shift in the scientific interpretation of both the chemical composition and behavioral variables in action in the Earth’s subsurface.

In the years following Mohorovičić’s treatise, the growing international community of geologic and seismological scholars began to utilize his methods to confirm the existence of his hypothesized discontinuity under all seven continents and ocean floors. So influential was Mohorovičić’s work that the layer itself was named the Mohorovičić discontinuity, or Moho, in his honor. Mohorovičić died in Zagreb in 1936 at the age of 79.

Impact

Years after his retirement, Mohorovičić’s pioneering work in seismology would come to be regarded as well ahead of its time. Despite the use of largely primitive equipment and lagging communication times between his international colleges, Mohorovičić was able to make deductions that would be invaluable to future scientists in the field. His research would play an important role in the analysis of earthquakes well below the planet’s outer levels. Mohorovičić’s analysis of seismograph data would also be instrumental in the refinement of strategies utilized to locate earthquake epicenters. The ability to survey and analyze the effects of seismic shifts beneath the Earth’s surface led to improvements in both building design and construction as subsequent generations of scientists and engineers aimed to mitigate structural damage and loss of life from earthquakes.

Bibliography

Brush, Stephen. A History of Modern Planetary Physics: Nebulous Earth. Vol. 1. Cambridge, England: Cambridge UP, 1996. 145–47. Print. Discusses the relationship between Mohorovičić’s work and the Gutenberg discontinuity in the work of seismologists in the mid-1920s, and its implementation in research investigating the geological properties of the Earth’s core.

Monroe, James. The Changing Earth: Exploring Geology and Evolution. New York: Brooks, 2008. Print. Discusses the early discoveries related to the Earth’s mantle, with descriptive explanation of Mohorovičić’s initial experiments with data from varying seismic monitoring stations throughout western Europe.

Orlic, Mirko. “Andrija Mohorovičić as a Meteorologist.” Geofizika 24.2 (2007): 75–91. Web. 15 May. 2012. In-depth study of Mohorovičić’s early work in meteorology, including early research, instruments utilized, and extensive survey of findings. Discusses Mohorovičić’s transition from meteorology to pursuits related to geology and seismology.

Rothery, David, ed. An Introduction to the Solar System. Vol. 1. Cambridge, England: Cambridge UP, 2011. 43. Print. Survey of Mohorovičić’s career and conception of the Mohorovičić discontinuity and its relationship to the future location of earthquake epicenters.