This is a map from a newspaper, showing in red the areas destroyed by earthquake and fire in 1923. Virtually all of the "low city" was gone. There are many reasons for this. Everything was built with wood. Everyone cooked over fires, and that fire was generally the only source of heat in the house. And as I mentioned, the streets were exceedingly narrow, which allowed the fires to spread quickly. When they rebuilt after the earthquake, the governent mandated that there be wide avenues in all neighborhoods, to accommodate the heavy traffic a successfully rebuilt city would be sure to see. The real reason was that they wanted firebreaks. They didn't help in 1945, but those were special circumstances.