Do you remember what explosion it was that you heard 80km away? Because I seriously doubt any of the weaponry Russia has dropped so far can be heard anywhere close to that far.
Not OP, but I remember reports of https://en.wikipedia.org/wiki/Buncefield_fire explosion which wikipedia claims "Because of an inversion layer, the explosions were heard up to 125 miles (200 km) away".
In my original post I was referring to an explosion _inside_ Belgorod: https://www.reuters.com/world/ukraine-strikes-fuel-depot-rus... which may or may not be directly linked to the war; Ukraine has denied responsibility.