In the context here, Very-Long-Baseline Interferometry is used in radio astronomy for the purpose of triangulation of a specific point on the Earth’s crust. Radio emissions from quasars, which are millions to billions of light-years away, are generated as accretion disks collapse around supermassive black holes at the centers of galaxies. These radio emissions and their time difference are collected at various points around the globe for use in tectonic studies with precision on the order of millimeters.
