Well...
To be more specific, since I moved to this house I've been through over 1000 microquakes (those so irrelevant that only if we really pay attention we can notice and even so, we think a heavy truck passed 1 block away), 5 or 6 Light-moderate quakes (Still irrelevant, but enough to instantly say "Ouch, an earthquake", but no drop under the desk), 3 or 4 moderate-strong quakes (again, not enough to cause any life threat, but strong enough to trigger the Shakealert and make me drop under the table (yes, there was some minor damage) and only two "WTF" earthquakes (coincidently less than 24 hours apart from each other on 4th and 5th of July 2019.)
In terms of "engineering" Yes, having gas, it doesn't matter if it's propane or NG, is "more dangerous" than no gas at all. HOWEVER, during the two major earthquakes (Ridgecrest 2019) and the other moderate-somewhat-strong quakes, the seismic gas valves worked beautifully. (Only annoyance is resetting the valves and relight the pilots later)
In one of the quakes, the worst I felt, the wall furnace cover panels (Williams, I hate that) fell and broke the tiny gas pipe that goes to the pilot, but the valve triggered a couple of seconds later. It was enough to smell gas, the alarms went off, but at the same time (i was under the table, a few feet away from it) i could hear when the seismic valve triggered and shut off the gas.
If that's not enough, the meter has one more valve. After that earthquake stopped, I evacuated an immediately ran to the meter to close the valve but it was already closed.
So imagining the worst case scenario, a "badass" earthquake strong enough to break the NG pipes. there's a valve on each point of use (Furnace, stove, water heater, dryer) plus a valve next to the meter. The only gas left is the gas that is in the pipes. There's a risk of course, but the amount of gas isn't huge.
With propane, IDK if there is any sort of seismic valve. With the barbecue grill, for example if a major earthquake happens, there's absolutely nothing to shut it off automatically, OTOH, the tank is protected on the bottom of the grill and it will move together with it... When I'm not using the grill (or the patio heater), I always close the tank valve and, if an earthquake happens when I'm using the grill, of course my first reaction will be check the grill.
We had a minor quake and I have two of the very best earthquake early warning systems one can ever have (Dolby and Miele) They "go off" and start crying and running erratically average 1 minute before an earthquake. It happened once when I was grilling two hamburgers for breakfast and because of their reaction I instantly closed the tank valve and ran away from the grill (only to discover a few seconds later that they overreacted because of a micro quake weaker than my farts.)
The worst earthquake I felt wasn't the Ridgecrest. It was a silly 3.7 points but the epicenter was immediately below me. It lasted maybe 3-4 seconds and made a huge mess. (coincidentally it was the one that I had a minor gas leak mentioned above). When it happened, there was no warning at all (except Miele and Dolby) and I was standing. For days I could feel some pain on my ankles and knees, I could feel it throwing my almost 250 lbs up. It felt like the whole house jumped 1 inch in the air. Now I can say how the drinks feel in the cocktail shaker.
Back to the point...
I believe a well designed NG system and also portable appliances that use independent propane tanks are somewhat safe during a major earthquake. THey are, indeed, more dangerous than having no gas at all, but I refuse to see them as a massive danger as some people may think.
Of course, there's also a big difference between a single family home and a tall building with hundreds of points of use so my opinion doesn't apply for that because even if there were valves splitting the whole pipe into several small segments, the NG pipe diameter is so wide that a big amount of NG could still leak.