Is it Possible to Prepare for Liquefaction?
Reducing vulnerability and improving emergency response capabilities are two options to pursue in preparing for the possibility of liquefaction. With hazard zone maps, it is possible to identify areas potentially subject to liquefaction and to identify areas of minor and major concern. Emphasis in terms of developing appropriate public policy or selecting mitigation techniques should be in areas of major concern. (An example of an area of major concern in the San Francisco Bay area would be bay lands reclaimed by placing uncompacted fill under water.) Public and private property owners can use hazards maps to understand where the most serious damage can be expected and what structures are most vulnerable. This information, in turn, can be used to decide where limited resources should be concentrated and what mitigation strategies, if any, should be adopted. City and county governments can also use this information to decide if they want to regulate the risk through ordinance or code changes. If adequate maps exist, local governments could designate liquefaction potential areas, and require, by ordinance, site investigations and possible mitigation techniques for properties in these areas. Additional engineering could be required for new construction; essential services buildings could be strengthened or relocated; and additional redundancy could be built into lifelines systems, particularly underground pipes and critical transportation routes.
A call to the closest office of the U.S. Geological Survey is a first step in identifying available information. Liquefaction hazard zone maps, which are at the basis of developing regulatory strategies and other mitigation options, already exist for some of the most seismically active areas in the country.
What Are the Implications for Response?
Emergency response plans at the local jurisdictional level need to identify those areas most vulnerable to liquefaction. Sites where liquefaction can cause major problems can be identified using the liquefaction hazard or risk maps discussed above. Emergency plans might want to specify a reconnaissance survey of these areas immediately after an earthquake occurs. Problems resulting from liquefaction such as damage to underground pipelines also need to be factored into any emergency response planning. Emergency responders should expect interrupted water supply, and natural gas and sewage leaks. Back-up sources of water need to be identified or developed. In addition, the roadbeds in areas potentially subject to liquefaction may be seriously damaged, greatly complicating the ability to evacuate residents or to bring in emergency response equipment. These systems should have redundancy or alternatives.
What Are the Implications for Recovery?
Recovery and rebuilding in areas that have experienced damage due to liquefaction raise some special issues. One of the first decisions policymakers in the community face is whether to allow rebuilding in the damaged area. In the United States, it is most common for a jurisdiction to allow rebuilding, but with additional restrictions such as requiring detailed site investigations and possibly engineered foundations. The individual property owner also needs to decide if repair and rebuilding are feasible, particularly from a financial perspective. The community, usually a city or county, will need to decide if some sort of large- scale soil stabilization project should be attempted during rebuilding; one important determinant in this decision is the availability of funding. In general, for both individual property owners and public entities, it is much less expensive to reduce vulnerability to liquefaction before an earthquake than it is to pay for repair or retrofit measures after an earthquake. Once a community is in the process of rebuilding, community leaders and individual property owners should take advantage of every opportunity to mitigate the liquefaction risk.