2020 Local Hazard Mitigation Plan

City of Irvine

Civil Disturbance Climate change is not likely to impact future civil disturbances in Irvine. Cyber Threats Climate change is not likely to impact cyber threats in the future within Irvine.

Infrastructure Failure Infrastructure failure that is caused by other hazard types may be affected by climate change. Many infrastructure failure events are typically caused by some natural hazards (i.e., flooding, high winds, etc..). As discussed in the Severe Weather section, some severe storms are expected to become more intense because of climate change. This, in turn, may increase the frequency and/or severity of infrastructure failures. Climate change is also expected to increase the number of extreme heat events in Irvine, and as higher temperatures stress mechanical and electrical systems, it is possible that this effect may also increase the frequency or severity of infrastructure failure events.

Seismic Hazards

Seismic hazards of concern in Irvine include fault rupture, liquefaction, and seismic shaking.

Description

Fault Rupture The shifting and movement of the Earth’s tectonic plates are responsible for seismic events. These tectonic plates can pull away from, move toward, or pass by each other. As they do, the plates sometimes lock together. This creates tension, and eventually, the built-up tension is released like a springboard. The tension dissipates into the Earth’s crust. The location at which two tectonic plates join is called a fault line. Fault lines are sometimes visible on the Earth’s crust as sudden rifts or anomalies in the continuity of the landscape. In California, the major north - south fault line is the San Andreas Fault — where the North American and Pacific Plates meet. Constant friction between the two plates over the millennia, however, has caused the areas where the two plates intersect to become fragmented, creating new, smaller faults. The area in the immediate vicinity of a fault line is at risk of damage due to the potential for a fault rupture — the deformation or displacement of land on either side of the fault, which may move a few inches to several feet in opposite directions. Any buildings or infrastructure situated around, on top of, or across a fault line could potentially be severely damaged or destroyed. The direction of the fault rupture depends upon the fault type: dip-slip faults produce vertical shearing, strike-slip faults produce horizontal shearing, and oblique-slip faults produce both vertical and horizontal shearing. A fourth kind of fault, called a “blind” fault, produces virtually no visible displacement of land. Some faults have emerged recently in geologic history. Quaternary faults are faults that have developed any time between the Holocene Era and the present (within the last 1.8 million years). These faults are especially concerning since they are the most likely to be active and cause future earthquakes. The Alquist-Priolo Earthquake Fault Zoning Act enables the California State Geologist to designate zones surrounding active faults as Alquist-Priolo Special Study Zones, which is a special regulatory zone that

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