San Diego is located in a seismically active region, placing the area at risk for earthquakes, a common occurrence throughout California. Understanding the specific fault systems and the nature of seismic activity is important for residents and visitors.
Major Fault Systems in the Region
San Diego is directly impacted by several active fault systems, with the Rose Canyon Fault Zone being the most immediate concern. This fault runs directly through downtown San Diego, extending offshore along the coast and beneath San Diego Bay, making it a significant seismic hazard due to its proximity to populated areas. While its last major local rupture occurred centuries ago, experts estimate it is capable of producing earthquakes in the magnitude 7.0 to 7.2 range. The Rose Canyon Fault is also linked northward to the Newport-Inglewood Fault, forming a longer interconnected system.
Further inland, the Elsinore Fault Zone represents another significant seismic source for the region. This fault extends through San Diego County, passing through areas like Lake Elsinore, Palomar Mountain, and Julian. The Elsinore Fault is one of Southern California’s largest, capable of generating events between magnitude 6.5 and 7.5, with a maximum credible event estimated at magnitude 7.6. The San Jacinto Fault, known for being more active than the San Andreas, also traverses northeast San Diego County and can produce earthquakes up to magnitude 7.6. Though the San Andreas Fault is over 60 miles from San Diego’s most populated areas, a major rupture could still send strong tremors across the region.
Understanding Seismic Activity
San Diego experiences frequent seismic activity, though most earthquakes are too small to feel. San Diego County averages about 6,900 quakes of magnitude 1 or higher per year, and roughly six quakes of magnitude 4 or higher annually.
Historically, San Diego County has experienced five earthquakes above magnitude 7 since 1900, occurring roughly every 23 to 27 years. The Rose Canyon Fault remains a concern, with studies suggesting an 18% probability of a magnitude 6.7 or larger earthquake on or around it within a 30-year period. Specific areas within San Diego, such as Mission Valley, are susceptible to liquefaction during intense shaking, where saturated soil temporarily loses strength and behaves like a liquid.
Mitigating Earthquake Risk
San Diego has implemented various measures to address earthquake risks. Modern building codes enhance the structural integrity of new constructions, helping them withstand seismic forces. Efforts also focus on improving the resilience of existing infrastructure, including bridges and utility systems, to ensure they can continue to function following an earthquake.
City planning incorporates a seismic safety element to identify hazards and guide land use decisions. Emergency services continuously develop and refine plans for earthquake response. The San Diego Earthquake Scenario, which models a magnitude 6.9 earthquake on the Rose Canyon Fault, helps experts understand potential impacts and develop strategies to improve regional earthquake resilience.
Personal Preparedness
Individual preparedness is a simple yet effective way to manage earthquake risk. Creating an emergency kit is a fundamental step. This kit should include:
At least a three-day supply of water (one gallon per person per day)
Non-perishable food
A first-aid kit
Essential medications
A flashlight with extra batteries
A battery-powered radio
Some cash
It is also important to have a family communication plan, designating an out-of-area contact who can coordinate information if local communication is disrupted. Secure your living space by bolting tall furniture like bookcases to wall studs and strapping water heaters to prevent them from toppling during shaking. During an earthquake, the recommended action is “Drop, Cover, and Hold On”: drop to the ground, take cover under a sturdy table or desk, and hold on until the shaking stops, protecting your head and neck.