Defining the Mohorovičić Discontinuity (Moho)
The Mohorovičić Discontinuity, commonly known as the Moho, is the boundary within Earth's interior that separates the crust from the underlying mantle. It represents a significant change in rock composition and physical properties, marking the base of the crust.
Detection Through Seismic Waves
The Moho is primarily identified by a distinct and sudden increase in the velocity of seismic P-waves (compressional waves) and S-waves (shear waves) as they travel deeper into the Earth. This abrupt change in speed indicates a transition from the less dense, brittle rocks of the crust to the denser, more rigid rocks of the mantle.
Location and Significance
The depth of the Moho varies considerably across the globe, typically ranging from about 5-10 kilometers (3-6 miles) beneath oceanic crust to 20-90 kilometers (12-56 miles) under continental crust, being deepest beneath major mountain ranges. Its existence is crucial for understanding the layered structure, composition, and dynamics of Earth's internal layers.
Discovery and Importance to Geophysics
The Moho was discovered in 1909 by Croatian seismologist Andrija Mohorovičić, who observed the abrupt change in seismic wave speeds during an earthquake. His groundbreaking discovery provided the first clear evidence for a distinct boundary between the crust and mantle, fundamentally shaping our understanding of planetary geophysics.