Most earthquakes occur in the earth's crust, at a depth of less than 50 km. These are known as . However, in some regions of the globe, earthquakes occur at greater depths, up to around 680 km. These earthquakes are called " intermediate " if they occur down to a depth of around 300 km, and " deep " if they occur beyond that. While rocks are brittle at ambient temperature and pressure, which makes it possible to understand the instantaneous fracturing at the origin of surface earthquakes, at greater depths, deformation under the effect of tectonic forces is expected to occur plastically, without generating perceptible vibrations. Understanding the physical phenomena behind deep earthquakes is one of the major issues in current geophysical research. Although generally unperceived by humans, deep earthquakes played an important role in the plate tectonics revolution and in the construction of the first models of the earth's internal structure. I devoted four one-and-a-half-hour lecture sessions to this fascinating subject in October and November 2018.
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Lecture
Deep earthquakes
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