San Diego's earthquake threats
The Rose Canyon Fault, and other local faults, are “all over San Diego, but we really don’t have effective mapping of them,” a local professor said. Times of San Diego takes a look at what the experts know about the possibility of a major quake and the impact it would have on the city and region.
What could a Rose Canyon rupture do?
Coastal areas from Mission Bay to Imperial Beach are especially vulnerable to earthquakes due to liquefaction, where intense ground shaking causes wet soil to behave like a liquid. Artificially filled areas are at greater risk, including Mission Bay, Coronado and the airport.
Structures in these areas are at risk of sinking into the ground, according to Chaddock, the City College professor.
“I was at Lake Murray when it experienced liquefaction,” Chaddock said. “I was sitting at one of the tables next to the lake, and I saw how big it was because the water was coming up around the table. If you’re close to the water table, it’s going to come to you.”
San Diego’s pioneers built much of the city before anyone recognized the area’s seismic dangers.
Experts now know to expect widespread damage. The 2020 report estimates a Rose Canyon earthquake would cause $38 billion in building and infrastructure damage, affecting 120,000 buildings total — with 8,000 damaged beyond repair.
Casualty estimates range between 7,700 to 13,600 people injured, with 300 to 800 killed depending on time of day — a daytime quake is thought to be the most potentially catastrophic. An estimated 36,000 households will be displaced in the aftermath.
Chaddock compared the expected damage to the 2011 Christchurch earthquake, which killed 185 people and injured several thousand on New Zealand’s south island.
“Old buildings especially came down. Downtown shook apart. Along the fault line especially, stuff came apart,” she said. “Some of the older places, pre-1995, maybe pre-2000, they may not do well.”
What does that mean for San Diego? The majority of local buildings went up in the 1970s and 1980s, when construction methods provided less protection from seismic hazards.
Certain types of buildings are most at risk, especially unreinforced brick structures and soft-story residential and commercial buildings, which lack seismic supports that protect lower floors from shaking. Modern seismic safety standards were adopted in 1997, then expanded in the 2019 version of the California Building Code.
Modern buildings are expected to survive the 6.9-earthquake scenario, but San Diego County has up to 8,100 vulnerable structures.
Reinforced public structures are also expected to survive, including freeways, bridges and pipelines. San Diego’s water supply infrastructure has been strengthened by the County Water Authority. Water flows through reservoirs and aqueducts from east to west.
However, infrastructure near the coast directly above the Rose Canyon Fault still faces risks. The report estimates that damages will include more than 14,000 water system leaks. This is expected to leave coastal communities from La Jolla to Point Loma and Coronado without water for weeks — or even months.
The wastewater pipelines connecting to the Point Loma Wastewater Treatment Plant also are at risk. Breaks in the system are expected to cause countywide disruptions to treatment and the release of sewage in the San Diego River, the Pacific Ocean and both San Diego and Mission bays.
The report describes the system as San Diego’s “Achilles heel.” Similar to the water system, coastal wastewater management would be out of commission for weeks to months.
The earthquake scenario also considers the impact of widespread power outages. Strong shaking and ground failure could damage substations, transmission lines and local infrastructure along the dense coastal corridor. Loss of electricity would further strain water pumps, wastewater facilities, hospitals and emergency response systems already hard hit by the quake.
San Diego’s Public Utilities Department emphasizes that its water and wastewater systems are designed with multiple layers of redundancy to reduce service disruptions during emergencies, including backup generators, alternate pipelines, storage reservoirs, duplicate equipment and diversified water sources.
An example is the 2024 upgrade to Pump Station 2, which handles nearly 90% of the city’s sewage flow and now has expanded standby power capacity in the event of a major outage.
Officials acknowledge that a large earthquake could still damage pipelines and infrastructure despite these preparations, but say the goal is to minimize disruptions, protect public health and restore services as quickly as possible.
