Answer:
Very bad. We are talking about some next level stuff, the SF earthquake of ‘06 was very deadly, it killed tens thousands and leveled half the city. You see, most of the buildings of the time were structurally made from wood, and weren’t strong enough to withstand the earthquake. Also wood burns so the city had a massive fire. Fires spread across the city which also contributed to deaths. That’s a significant percentage of the population dead, and only god knows the economic damage.
