The Hayward fault is considered to be particularly dangerous due to the poor soil conditions in the alluvial plain that drops from the East Bay Hills to the eastern shoreline of San Francisco Bay . At the lower elevations near the bay the soil is mostly water saturated mud and sand , placed in the early 20th century as fill in marsh areas . This soil tends to amplify the effects of an earthquake and so producing significantly greater ground motion . Additionally , the soil itself can fail , turning into a liquid mud from the agitation , a mud unable to support buildings erected upon once-firm soil . This region is also covered with dense low-rise urban development , most of which was built soon after the 1906 San Francisco earthquake , and long before even moderately earthquake resistant construction practices had been developed in the late 1920s
1906 San Francisco earthquake
1906 San Francisco earthquake
Hayward Fault Zone