City of Irvine
2020 Local Hazard Mitigation Plan
While farmers in the area most likely felt powerful seismic shaking, it is unlikely that they experienced significant property damage as other more urbanized areas in the region reported. Other strong, regional earthquakes have occurred in the Southern California region, but their epicenters have been so distant from Irvine that seismic shaking generated by the earthquake did not cause significant property damage or harm to the City. Table 3-13 shows significant earthquakes – magnitude 6.0 M w or greater – that have occurred within 100miles of Irvine since the beginning of the 20th century. Authorities made disaster declarations in Orange County for the 1994 Northridge Earthquake and 1987 Whittier Narrows Earthquake, although there was no substantial damage in Irvine from either earthquake. 90,91
Seismic shaking primarily affects unreinforced masonry buildings, as seen here with this Long Beach middle school damaged by the 1933 Long Beach earthquake. Image from Los Angeles Times.
Table 3-13: Significant Earthquakes (6.0+ Mw) Within 100 Miles of Irvine 92 Event Name Distance (Miles)* Magnitude 1933 Long Beach Earthquake 12 6.4 1937 Oasis Earthquake 92 6.0 1948 Desert Hot Springs Earthquake 88 6.0 1971 San Fernando Earthquake 61 6.6 1986 North Palm Springs Earthquake 72 6.0 1992 Joshua Tree Earthquake 87 6.1 1992 Big Bear Earthquake 66 6.3 1994 Northridge Earthquake 56 6.7 * Distance between the epicenter and Irvine Civic Center
Risk of Future Events
Fault Rupture Given the presence of faults within the City, it is likely that fault rupture could occur in the future. However, without further study of the fault segments within the City, it is difficult to estimate how often seismic events could occur along these segments. Liquefaction Due to the types of soil in Irvine and the surrounding area, the City will be perpetually at risk of a liquefaction event if the water table remains as high as it is. Since liquefaction events are triggered by seismic shaking, the probability of a liquefaction event occurring depends on the likelihood of an earthquake. An earthquake could occur along the numerous local faults running through Orange County that may lead to a liquefaction event. The likelihood of one of these local faults experiencing an earthquake powerful enough to trigger a liquefaction event within the next 25 years, however, is
72
Made with FlippingBook HTML5