Portrait of Andrija Mohorovicic (1857-1936), Croatian geophysicist. Mohorovicic was born at Volosko, now part of Yugoslavia. His best research was done following the 1909 Balkan earthquake. Studying the wave patterns from this, Mohorovicic deduced that the Earth's outer crust rested on a deeper layer that was more rigid, and through which shock waves travelled more rapidly. The boundary he showed was sharp rather than gradual, now called the Mohorovicic discontinuity. It is now known that this lies between ten and 40 miles below the surface. Mohorovicic's work changed the science of seismology, and has allowed a far better understanding of the Earth's structure.