How does the ITRS frame related to ECEF frame? How does the International Terrestrial Reference frame related to the Earth-centered, Earth-fixed frame, as both of them rotate with the Earth?
The simple explanation:
The International Terrestrial Reference (ITR) Frame is an Earth-centered, Earth-fixed (ECEF) frame, but with the axes of the ITR frame precisely specified taking into consideration the movements of the Earth's crust due to plate tectonics.

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