The 1989 Loma Prieta earthquake caused a total of $5.9 billion in property damage. Most of the damage was due to ground shaking. However, approximately $100 million of that (1.6%) was due to liquefaction (Holzer, 1998, p.B4). We were lucky. In 1906, liquefaction-related damage to water supply pipelines prevented containment of the fire in San Francisco that destroyed about 500 city blocks. Thus, liquefaction can be indirectly blamed for 85% of the total damage to San Francisco in 1906 (Youd and Hoose, 1978).

When the ground liquefies, sandy materials saturated with water can behave like a liquid, instead of like solid ground. The ground may sink or even pull apart. Sand boils, or sand "volcanoes," can appear.

Liquefaction can cause ground displacement and ground failure such as lateral spreads (essentially landslides on nearly flat ground next to rivers, harbors, and drainage channels) and flows.

Our most vulnerable land falls into two general categories:

	areas covered by the huge amount of fill poured into San Francisco Bay since 1845 to transform 77 square miles (200 square km) of tidal and submerged areas into land; and
	areas along existing and filled stream channels and flood plains, particularly those areas with deposits less than 10,000 years old.