Hiding a subterranean alien megastructure

I need to know if it'd be possible for a underground ring-like structure of immense proportions and alien design to go unnoticed by modern day sonar, radar, and geological surveying.

For an idea of size, imagine a tunnel about the width of a football field or bigger (maybe 100-200 meters in diameter) that's buried 2- 5 kilometers underground and wraps around the entire planet (giving it a circumference of 40000 km).

Could something like this remain hidden until a mining project accidentally uncovers it in Africa, or would something this size have been detected by now with the technology developed in the 20th and 21st centuries?

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Hiding a subterranean alien megastructure

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