The seismic hazard in our backyard — What San Diegans don’t know about the potentially deadly Rose Canyon Fault
Downtown San Diego seen from the Emerald Plaza helipad. Beyond the buildings, the Coronado Bridge cuts across the San Diego Bay. (Photo by Thomas Murphy/Times of San Diego)
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.
The unknown
Professor Tina Zeidan, who teaches geology at Southwestern College, thinks San Diegans focus too much on the famed San Andreas Fault, and too little on the earthquake danger in their own backyard.
“When I teach about earthquakes, I pull up a map,” she said. “I say, ‘We have a fault that runs right through San Diego, goes under the convention center and then through Mt. Soledad in La Jolla. Do you know the name of that fault?’”
“No one,” Zeidan said, “not one student in my 11 years of teaching, knows.”
The Rose Canyon Fault Zone is the primary seismic hazard through metro San Diego. Rapid, early urbanization covered the land in concrete and asphalt, blocking research efforts and leaving an unknown number of fault strands buried beneath aging infrastructure.
Unlike the San Andreas Fault — one of the most heavily studied fault systems in the world — scientists know comparatively little about the Rose Canyon Fault. Researchers say last week’s swarm of earthquakes outside San Diego was a reminder that anywhere in California — San Diego included — can abruptly become shaky ground.
As heavy machinery breaks ground downtown for development, crews are likely to discover seismic hazards running beneath their feet. These relatively common reveals come as little surprise to local geologists.
“They’re all over San Diego, but we really don’t have effective mapping of them,” said Lisa Chaddock, a professor of geology at San Diego City College who has surveyed local faults for the Department of Homeland Security.
Fault Line Park’s walkway follows the Rose Canyon Fault as it passes below the 14th Street and J Street intersection. The Pinnacle at the Park apartment towers overlook it to the east. (Photo by Thomas Murphy/Times of San Diego)
Discoveries of the local seismic network have and will continue to disrupt redevelopment plans downtown. This is evident at Fault Line Park, which exists because a fault cut through one side of a block being redeveloped. The company changed their design plans to position the park over the fault, in the shadow of two large residential towers.
The park’s mirrored metal spheres sit on either side of the fault line, acting as a “Fault Whisperer.” Visitors can listen to the Earth shift below their feet and look through one sphere at the other to see how much the ground has moved since they were installed in 2015.
Looking through one sphere at the other, visitors to Fault Line Park can see how the ground has shifted since 2015. (Photo by Thomas Murphy/Times of San Diego)
Experts indeed reserve their most hardcore earthquake anxieties for the San Andreas Fault — which extends along the coast from about 100 miles south of the state line through the Bay Area before shifting inland where it continues past Los Angeles and into the desert.
But those fears, experts argue, have led San Diegans to underestimate the risks they face when most of them live just 15 miles from the Rose Canyon Fault and other major fault lines.
“The things that are the most worrisome with the Rose Canyon Fault is the lack of knowledge and lack of understanding,” Chaddock said. “We don’t want to sound alarmist, but we don’t want people to not plan ahead.”
Seismic hazards in San Diego
The San Diego chapter of the Earthquake Engineering Research Institute spent five years creating a report, the 2020 Earthquake Planning Scenario, that estimates the impact of a 6.9 magnitude earthquake on the Rose Canyon Fault Zone that threatens San Diego and Tijuana. Residents would face catastrophe, according to the report, with one glaring vulnerability in particular should a major quake hit.
This network of earthquake fault lines comes in from the sea through Coronado, cuts through downtown and runs north below Interstate 5 until going offshore through Mt. Soledad — directly beneath the iconic cross.
Fault lines build up energy gradually as the ground on either side shifts. This happens at about the speed that human fingernails grow, a very slow process. An earthquake occurs when there is a sudden slip along a fault line, releasing the built-up energy in a rupture.
Rose Canyon is connected to other local fault lines, to the north in Orange County and to the south in Baja California. Both have produced damaging ruptures in the last century, including the 2010 Baja California 7.2 magnitude earthquake that shook up San Diego County on Easter.
There are also active offshore fault lines, which also are not well understood but are known to cause 7.0 earthquakes. These led to the 1986 Oceanside earthquake, killing one resident and injuring at least 29.
Professor Thomas Rockwell at his underground office at San Diego State. (Photo by Thomas Murphy/Times of San Diego)
Professor Thomas Rockwell is a leading geological scientist in San Diego; many of the county’s geologists learned what they know in his San Diego State classroom. Rockwell’s contributions to local research helped form the foundation for the 2020 report.
The last earthquake on the Rose Canyon fault occurred before the California missions were built, likely in the 1700s, according to Rockwell’s observations. On average, the fault has a 6.9 magnitude earthquake about every 700 years.
“We’re probably not going to have one for a couple hundred years, but the fickle thing about recurrence intervals on faults is that they have a fairly high coefficient of variation,” Rockwell said. “That means that, even though the Rose Canyon fault ruptures on average every seven hundred years, it doesn’t mean it couldn’t happen sooner than that.”
“We should still be prepared for an earthquake.”
Background earthquakes are another cause for concern. A magnitude 6 earthquake hit San Diego in 1862, causing a visible rupture in Old Town.
“We can have magnitude 6 on any of these faults anywhere in California as a random background earthquake,” Rockwell said.
Earthquake magnitude scales up based on the size of the rupture and the amount the ground shifts along a fault. For every level of magnitude, there is a tenfold increase in shaking. These background earthquakes are “not considered one of the big ones, but a six would still do a lot of damage,” according to Rockwell.
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.”
Highlighted yellow areas show areas at risk of liquefaction. Red lines show active fault lines recorded in 2016. (Image courtesy of San Diego Geologists)
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.”
Number of housing structures built in each decade. Over 250,000 units were built in the 1970s. (Image courtesy of San Diego Geologists)
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.
Water transmission infrastructure in relation to scenario earthquake shaking intensity on the Rose Canyon Fault. (Image courtesy of San Diego Geologists)
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.
What is being done?
Many agencies across the county have been hard at work improving seismic safety. Interstate 5 is at particular risk if there is a rupture along Rose Canyon, so efforts have been made to strengthen it.
“Caltrans, based on our earlier work, has structurally reinforced a lot of the bridges in San Diego because they weren’t designed for as strong of an earthquake as we know we can have,” Rockwell said. “They’re strengthening the pillars. I know that they enhance the diameter, the support structures themselves, to be stronger.”
Southbound traffic on Interstate 5 approaching Pacific Beach from Mt. Soledad. The Rose Canyon Fault runs directly below this stretch of road. (Photo by Thomas Murphy/Times of San Diego)
Behind the scenes, many agencies — like Caltrans — have taken steps in case disaster strikes.
San Diego’s Office of Emergency Services hosted a city-wide, collaborative training session to improve communication between local, state, federal, military, utility and nonprofit organizations during a simulated major earthquake. The agencies met at the end of April, which the California Governor’s Office of Emergency Services designated as Earthquake Preparedness Month.
What can you do?
Many public agencies provide tips on how to be prepared in the event of an earthquake or other disaster. Insurance is another matter.
Less than 20% of Californians have earthquake insurance, something not included in standard homeowners insurance packages. And most San Diegans live within several miles of a fault. The California Earthquake Agency, the largest provider of this coverage, encourages residents to be prepared.
Zeidan asks her students to read through their insurance documents to confirm whether or not they will be covered if a major earthquake strikes along the Rose Canyon Fault.
“People don’t like to put themselves in the worst-case scenario, but if we have a really big earthquake, people are dependent on the government for running water. That might be a week or more before they can come and fix system-wide water, sewage and electricity,” she said.
At the end of the Rose Canyon Fault lesson, Zeidan asks the class whether or not they feel prepared for an earthquake.
“Most of the time, the answer,” she said, “is ‘No, I’m really not prepared.’”
» Originally published by Times of San Diego on May 15, 2026.