Buildings are not consistently more likely to be damaged to the point of being uninhabitable in areas mapped as having high or very high liquefaction susceptibility than outside of those areas, given equivalent shaking intensities. However, if a building is damaged by liquefaction, it is likely to have more extensive damage, and damage that is more costly to repair.

ABAG examined the percent of homes red-tagged as uninhabitable after the Loma Prieta earthquake within and outside of areas mapped as having high or very high susceptibility to liquefaction. The fraction of pre-1940 single-family homes red-tagged in areas of high and very high liquefaction on the ABAG liquefaction susceptibility maps is about equivalent to two times less than outside of these areas, given equivalent shaking intensities. This apparent anomaly is consistent with damage patterns of four-story apartment buildings in the Marina District of San Francisco analyzed by Harris and Egan (1992): "The ground failure in the central part of the filled area appears to have mitigated much of the potential damage by dissipating seismic energy through liquefaction." Thus, some speculate that liquefaction may be viewed as a type of "natural" base isolation system. ABAG did not, however, examine the cost of repairing damaged homes after the Loma Prieta earthquake. (See Appendix C for more information.)

On the other hand, U.S. Geological Survey researchers examined data following the Northridge earthquake. "In the Balboa area, where most of the ground failure occurred, construction type and home vintage are nearly identical to the study area as a whole. …Average repair costs for the 315 properties impacted by ground failure…are found to be approximately 300% higher than for the 4,514 properties located outside of ground failure zones ($32,578 vs. $10,771). … Notably, over 6% of damaged homes affected by ground failure required demolition of both structure and foundation, as opposed to only 0.2% of homes unaffected by ground failure. Likewise, foundation repairs needed to be performed on 27.5% of damaged structures in ground failure zones as opposed to only 5% of damaged structures outside of these zones" (D. Ponti, personal comm., 1998).

The Seismic Hazard Mapping Program (SHMP) and Act were modeled after the earlier Alquist-Priolo Earthquake Fault Zoning Act that deals with fault surface rupture. The SHMP program is intended to protect public safety from the earthquake effects of strong ground shaking, liquefaction, landslides, or other ground failure. As with the earlier mapping act, the implementation focus is on "structures intended for human occupancy." Thus, the focus of this program is on buildings and other structures, not on transportation and utility lifelines. This focus is consistent with that of the engineering community.

Based on the findings of ABAG and others, local governments reviewing proposed developments should expand on this program to ensure that transportation and utility systems are designed to minimize disruption, as well as note potential problems in emergency response due to likely utility disruptions and road closures.