Very-long-baseline interferometry (VLBI) is a type of radio telescope interferometry where the necessary timing is stored at each telescope and later analysis is used to determine the direction from which the signal came, allowing telescopes far apart to be used. It has achieved angular resolution in the 10 microarcsecond range.
While it clearly is useful for observing sufficiently bright radio sources, it offers as a byproduct, measurement of changes in the distance between receivers, down to the millimeter range, thus reveals the effects of plate tectonics.
The arrays often use existing telescopes, and may be short-term projects, e.g., for specific surveys. Some VLBI arrays:
A recent development is electronic very-long-baseline interferometry, which is near-real-time transmission of the data for immediate analysis.