Re: I'm very dubious about this
Err, there's an explanation right in the Global Times article which El Reg references in the second paragraph of their story.
Here's one example of how seismic data can be used for nefarious purposes:
"By obtaining relevant data from seismic monitoring centers, hackers can deduce the underground structure and lithology of a certain area," the expert said. "For example, it can be inferred whether there is a large underground cavity, and thus whether it might be a military base or command post."
Seismic intensity data is closely related to national security, for instance, some military defense facilities need to take into account factors such as seismic intensity, experts said.
So hypothetically you hack into a country's seismic monitoring system and wait for an earthquake. You then analyze the data to get an idea of the regional geology and how it relates to large underground command posts or aircraft shelters (whose location you find by other means) which you then use to decide how big of a nuclear bomb to use on that target. Then when you decide to start WWIII you have a slightly better idea of what to nuke and how.
What is it you imagine that the US do when they spend many, many, billions of dollars per year on their offensive "cyber" operations? The NSA (etc.) spies don't all spend their entire day playing video games and posting on Facebook. They spend at least some of it hacking into all and sundry, as the Germans (and others) have found out to their cost as one very well known example.