Maybe a few 1st strikes with a few MOAB's would help.
Wouldn’t do a lot of good. There are too many of them, concealed in solid bunkers. They have constructed thousands of caves and supply tunnels in the mountains to supply the guns, which can retract immediately after firing. They are scattered all over the hills, and we couldn’t even find them until they fired. We’d have to first find the gun, by waiting for it to fire, then take it out individually. While we get one gun, hundreds more will be lobbing bombs (and maybe more?) into the city.
Unless we nuke the hills, which we won’t, the artillary will decimate the civilian population until troops battle up there and take them out.
The US Army has successfully shown an repeated ability with its THEL high-power lasers ( as of two years ago, link requires Acrobat Reader) to track and blow-away artillery shells in flight! Deploy a couple hundred of these to cover most of the ballistic paths to Seoul from the known cannon locations, and we will have an all new regional situation. In view of the 'use it or lose it' mentality alluded to in the article, I would get the system 100% deployed BEFORE the North Koreans catch wise of it. Tell the locals that we are putting in 'weather-tracking' installations. Lead Weather. Once the NK attack is launched and blunted, the US JDAMs can crush the tunnel entrances of all the artillery. Prioritization of so MANY targets will be a bitch though. Particularly since the NK Army won't be standing idle, but will be popping up behind SK lines through their tunnels, their own flanking amphibious assaults, and even driving straight down that stupid railway opened up between the North and South by the incredibly credulous Southerners...