Well, your textbook is slightly off. 63 people, not 30,000 died 
. I hope this is just a simple, baseless story, and not an embellishment of the San Fransisco quake, because this is more DPRK then PRC.
The Loma Prieta earthquake wasn't anywhere close to 8.2 magnitude anyway. Not to mention that no natural disaster has caused that much loss of life in the United States (biggest was the 1900 Galveston hurricane killing 8,000). I'm guessing that this is a totally fictional story that just happened to be set in the same year as a significant real life earthquake.
