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2021 Multijurisdictional Local Hazard Mitigation Plan 10.4.1 Population Community Members of High-Risk Areas The degree of vulnerability is dependent on many factors, including the age and construction type of the structures people live in, the soil types their homes are constructed on, their proximity to fault location, etc. It is estimated that 38.6 percent of San Mateo County’s population resides on soil classes considered susceptible to ground shaking from earthquakes (NEHRP Class D and E soils). An analysis was performed of the population living in these susceptible areas using the SoVI ratings (see Section 7.2.2). Detailed results by jurisdiction are in Appendix E. Table 10-6 summarizes results for the overall planning area. Table 10-6. Distribution of Population Exposed to Earthquake Hazard by SoVI Rating SoVI Rating Population Living in Exposed Areas Having the SoVI Rating Shown Number of People % of Total Exposed Population Very High 37,073 12.72% Relatively High 86,842 29.79% Relatively Moderate 74,000 25.39% Relatively Low 59,263 20.33% Very Low 34,301 11.7% Estimated Impacts on Persons and Households Hazus estimated impacts on persons and households in the planning area for the four selected earthquake scenarios as summarized in Table 10-7. Table 10-7. Estimated Earthquake Impact on Persons Scenario Displaced Households Persons Requiring Short-Term Shelter Number % of Total Number % of Total 100-Year Probabilistic 587 0.08% 342 0.04% San Andreas Fault Scenario 1,977 0.26% 967 0.13% San Gregorio Fault Scenario 264 0.03% 121 0.02% Butano Fault Scenario 15 0.002% 6 0.0008% Monte Vista Fault Scenario 513 0.07% 249 0.03% 10.4.2 Property Building Age Table 10-8 identifies significant milestones in building and seismic code requirements that directly affect the structural integrity of development. Using U.S. Census estimates of housing stock age, estimates were developed of the number of housing units constructed before each of these dates. More than 7 percent of the planning area’s housing units were constructed after the Uniform Building Code was amended in 1994 to include seismic safety provisions. Housing units built before 1933 when there were no building permits, inspections, or seismic standards, account for 7.6 percent. Many of the housing units in the planning area are detached, single-family residences of wood construction, which generally perform well during earthquake events. 10-20