A South Korean security analyst suggested that DPRK artillery pieces of calibers 170mm and 240mm "could fire 10,000 rounds per minute to Seoul and its environs." The number of Koksan guns is not publicly reported, but it is reliably reported that North Korea has about 500 long-range artillery tubes within range of Seoul, double the levels of a the mid-1990s. Large caliber self propelled artillery pieces typically have a sustained rate of fire of between four and eight rounds per minute. This suggests a total rate of fire of artillery alone of between 2,000 and 4,000 rounds per minute. The DPRK's two hundred 240mm MRLS's fire either 12 or 22 rounds, providing a maximum single salvo of no more than 4,400 rounds.
Since it usually takes about ten minutes to reload an MRLS, these systems could fire six salvoes an hour.
Based on the above information, the absolute most the North Koreans would be able to fire at Seoul that first hour, not taking into account any counter-battery fire, is 266,400. Realistically, the rate of fire will likely be about half of this. During this recent artillery duel, the South Korean Air Force responded within four minutes and the South Korean artillery within thirteen minutes. This would likely result in a significant portion of their artillery and rocket launchers being knocked out or forced to relocate before the first hour is up.
Don't get me wrong; an attack on Seoul would be devastating and would result in thousands, possibly tens of thousands, of casualties, but it isn't quite the doomsday scenario that this article suggests.
As I’ve seen happen a lot, the original article conflated the artillery pieces in range of Seoul, with the total rate all NK artillery could fire over the ENTIRE DMZ.
Only a fraction of NK artillery has enough range to reach Seoul and is close enough to do so.
Cities and their citizens are a lot tougher than people imagine, as was found out in WWII.