Just to add my own experiences … the first was in San Francisco in 1989 (the Loma Prieta earthquake 7.0). I had an appointment in Oakland, and on the way there received a call to tell me that it had been cancelled. So I decided to just play tourist.
I was sitting at traffic lights, when the car started to move. I pushed harder on the brake, but the sensation continued. Then I noticed that I wasn’t really moving, but the street lights were whipping back and forth, and the traffic lights went out. It dawned on me what was happening, and sat in the car looking up at the tall buildings around me…
The movement stopped, so I decided to see what was going on, and headed up to the highest bit of land around (Coit tower). There was not a lot of obvious damage. Some buildings had cracks, and small piles of bricks on the sidewalk, but didn’t see anyone injured.
One thing that did strike me, was how well behaved drivers were being without traffic lights. They just treated every intersection as a four way stop (For non US readers, the US has crossroads where there are no lights, There is a STOP sign in every direction, drivers keep track of who arrived when, and take their turn to go). On the intersections where there was a busy road and a small road, with a big traffic imbalance, someone would walk into the middle and begin directing traffic. I was living in Paris at the time, so this was amazing to me - I could just imagine what would happen if the lights went out there — instant gridlock.
Got to Coit tower, and looked around. The entire bay seemed to have no power, there was smoke rising from the Oakland side, and a lone Navy helicopter was cruising around the bay checking things out. On the San Fran. side there was smoke starting to rise from the Marina District - that was mainly housing built on landfill used to recover some of the bay from the sea.
As I watched it grew dark. There was now a red glow in the sky from the fires in the Marina District. I turned around and looked back at the city, at a sight I don’t suppose I will ever see again: San Francisco completely dark, except for rivers of red and white (roads with cars all trying to get home).
I decided to try to get back to my hotel, in Palo Alto, which is a few miles south of SF. Traffic was not moving fast, and stopped frequently. Of course each time it stopped, i was under a bridge …
Got back to the hotel. The staff had broken all the doors open to check if anyone was trapped. Not that it made any difference, none of the doors fit in their frames now anyway.
Then I decided to call my wife (in France) before she got up, turned on the news and saw what had happened. There was a long line for the one working phone. It was AT&T and they didn’t/couldn’t take Visa to pay for the call, they wanted an AT&T calling card. I explained that I didn’t have one - I did have a France Telecom phone card. The girl on the switchboard must have taken pity - she took that number (never saw a charge) and let me call home.
It dawned on me later that if my appointment hadn’t been cancelled, I would probably have been half way across Bay Bridge when that hit - around the part that collapsed …