Random thoughts about the difficulties from someone who definitely isn't an expert:
Low frequency noise is harder to block with materials, so you can't put a microphone in a foam box with one side open then swing it around looking for the direction the sound is loudest.
If it travels further (I guess it should if it's harder to block) then there's a greater chance anything you can hear is coming from further away.
If it's far away, it's harder to triangulate (because you need to go further between measurements).
If it's shaking the ground, does that mean the strength only falls off linearly? Do you get surface 'waves' that are then only spreading out linearly?
edit - This is a really interesting question though, I guess it is fairly hard, but it does feel like it should be simple.
If it's shaking the ground, then every surface near you (which is sufficiently rigidly attached to the ground) will be producing sound waves. Hence even if you can identify a direction to the sound, it's probably a red herring.
Low frequency noise is harder to block with materials, so you can't put a microphone in a foam box with one side open then swing it around looking for the direction the sound is loudest.
If it travels further (I guess it should if it's harder to block) then there's a greater chance anything you can hear is coming from further away.
If it's far away, it's harder to triangulate (because you need to go further between measurements).
If it's shaking the ground, does that mean the strength only falls off linearly? Do you get surface 'waves' that are then only spreading out linearly?
edit - This is a really interesting question though, I guess it is fairly hard, but it does feel like it should be simple.