<P> The most important characteristic of the shaking intensity noted in Andrew Lawson's (1908) report was the clear correlation of intensity with underlying geologic conditions . Areas situated in sediment - filled valleys sustained stronger shaking than nearby bedrock sites, and the strongest shaking occurred in areas of former bay where soil liquefaction had occurred . Modern seismic - zonation practice accounts for the differences in seismic hazard posed by varying geologic conditions . The shaking intensity as described on the Modified Mercalli intensity scale reached XI (Extreme) in San Francisco and areas to the north like Santa Rosa where destruction was devastating . </P> <P> Although the impact of the earthquake on San Francisco was the most famous, the earthquake also inflicted considerable damage on several other cities . These include San Jose and Santa Rosa, the entire downtown of which was essentially destroyed . </P> <P> As damaging as the earthquake and its aftershocks were, the fires that burned out of control afterward were even more destructive . It has been estimated that up to 90% of the total destruction was the result of the subsequent fires . Within three days, over 30 fires, caused by ruptured gas mains, destroyed approximately 25,000 buildings on 490 city blocks . One of the largest of these fires was accidentally started in a house on Hayes Street by a woman making breakfast for her family . This came to be known as the "Ham and Eggs Fire". Some were started when firefighters, untrained in the use of dynamite, attempted to demolish buildings to create firebreaks . The dynamited buildings themselves often caught fire . The city's fire chief, Dennis T. Sullivan, who would have been responsible, had died from injuries sustained in the initial quake . In all, the fires burned for four days and nights . </P> <P> Due to a widespread practice by insurers to indemnify San Francisco properties from fire, but not earthquake damage, most of the destruction in the city was blamed on the fires . Some property owners deliberately set fire to damaged properties, in order to claim them on their insurance . Capt . Leonard D. Wildman of the U.S. Army Signal Corps reported that he "was stopped by a fireman who told me that people in that neighborhood were firing their houses...they were told that they would not get their insurance on buildings damaged by the earthquake unless they were damaged by fire". </P>

Most of the destruction in san francisco following the earthquake of 1906 happened due to