I think you are looking at the photos backwards.
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The blue scree seen in that picture is not blown out from the entrance to the tunnels. The tunnel entrances are facing the other way. The tunnel complex extends from those impact points and connects to the center prong of the trident shaped road in the lower right.
The lower blue color swath seems to follow the presumed path of the underground tunnels. Not a shotgun discharge blasting out from the tunnel entrances. Something stirred up the surface above the tunnels enough to displace the normal top layer of dirt and reveal the underlying layer color. The same color seen in the scree piles.
This had to be a measurable seismic event. The only question is who or what would be listening for it? And who controls those seismographs? How far would a very shallow event radiate or be detectable?