Can Liquefaction Be Predicted?
Although it is possible to identify areas that have the potential for liquefaction, its occurrence cannot be predicted any more accurately than a particular earthquake can be (with a time, place, and degree of reliability assigned to it). Once these areas have been defined in general terms, it is possible to conduct site investigations that provide very detailed information regarding a site's potential for liquefaction.

Mapping of the liquefaction potential on a regional scale has greatly furthered our knowledge regarding this hazard. These maps now exist for many regions of the United States and Japan, and several other areas of the world. Liquefaction potential maps are generally compiled by superimposing a liquefaction susceptibility map with a liquefaction opportunity map. Liquefaction susceptibility refers to the capacity of the soil to resist liquefaction, where the primary factors controlling susceptibility are soil type, density, and water table depth. Liquefaction opportunity is a function of the intensity of seismic shaking or demand placed on the soil. Frequency of earthquake occurrence and the intensity of seismic ground shaking produced by those events are the major factors affecting liquefaction opportunity. To develop an opportunity map, an earthquake source model is required that includes locations of seismic source zones and quantitative estimates of the number and magnitude of the expected earthquakes in those zones.

These maps can be used in a variety of ways. At the local level in California, they have been incorporated as background documents in safety elements of the general plans that cities and counties are required to prepare. Although still not widely incorporated, information from these maps could also be translated into codes and ordinances. For example, the City of San Diego has developed and adopted provisions for the liquefaction hazard in its building code.
At the state level, the California Division of Mines and Geology is mapping liquefaction hazard zones throughout the state (CDMG, 1992). These zones are defined as areas meeting one or more of the following criteria:
(1) areas known to have experienced liquefaction during historic earthquakes;
(2) all areas of uncompacted fills containing liquefaction-susceptible material that are saturated, nearly saturated, or can be expected to become saturated;
(3) areas where sufficient existing geotechnical data and analyses indicate that the soils are potentially liquefiable;
(4) areas underlain with saturated geologically young sediments (younger than 10,000 to 15,000 years old).
Individual properties within these hazard zones will eventually be required to obtain a site-specific geotechnical investigation to define the liquefaction potential.