Item 26 - Updated Hazard Mitigation Plan

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Hazard Mitigation Plan | 2022 Earthquake Hazards - 69 - Q&A | ELEMENT B: HAZARD IDENTIFICATION AND RISK ASSESSMENT | B3a. Q: Is there a description of each hazard’s impacts on each jurisdiction (what happens to structures, infrastructure, people, environment, etc.)? (Requirement §201.6(c)(2)(ii)) A: See Impact of Earthquakes in the City below. Vulnerability of City to Earthquakes According to the 2021 County of Orange and Orange County Fire Authority Local Hazard Mitigation Plan, following major earthquakes, extensive search and rescue operations may be required to assist trapped or injured persons. Emergency medical care, food and temporary shelter would be required for injured or displaced persons. In the event of a truly catastrophic earthquake, identification and burial of the fatalities would pose difficult problems. Mass evacuation may be essential to save lives, particularly in areas below dams. Many families could be separated if the earthquake should occur during working hours. Emergency operations could be seriously hampered by the loss of communications and damage to transportation routes within, to and out of the disaster area and by the disruption of public utilities and services. Unless properly secured, hazardous materials can be released, causing significant damage to the environment and people. Extensive federal assistance could be required and could continue for an extended period. A significant earthquake (5.0 or greater) in the Orange County area or the region can strike without warning, and may create cascading effects including: • Earthquakes can cause large and sometimes disastrous landslides and mudslides. Any steep slope is vulnerable to slope failure, often as a result of loss of cohesion in clay-rich soils. • Earthquakes can also cause dam failures. The most common mode of earthquake-induced dam failure is slumping or settlement of earth-fill dams where the fill has not been property compacted. If the slumping occurs when the dam is full, then overtopping of the dam, with rapid erosion leading to dam failure is possible. Dam failure is also possible if strong ground motions heavily damage concrete dams. Earthquake-induced landslides into reservoirs have also caused dam failures. • Another secondary effect of earthquakes that is often observed in low-lying areas near water bodies is ground liquefaction. Liquefaction is the conversion of water-saturated soil into a fluid- like mass. This can occur when loosely packed, waterlogged sediments lose their strength in response to strong shaking. Liquefaction effects may occur along the shorelines of the ocean, rivers, and lakes and they can also happen in low-lying areas away from water bodies in locations where the ground water is near the earth’s surface. • Tsunamis can be formed as a result of undersea earthquakes of the Orange County coastline when huge amounts of energy are released as a result of quick, upward bottom movement. A wave is formed when huge volumes of ocean water are pushed upward. A large earthquake can lift large portions of the seafloor, which will cause the formation of huge waves. Impact of Earthquakes in the City Based on the risk assessment, it is evident that earthquakes will continue to have potentially devastating economic impacts to the City. Impacts that are not quantified, but can be anticipated in future events, include: ✓ Injury and loss of life ✓ Commercial and residential structural damage