As most of you already know, a 5.2 magnitude earthquake struck south of Julian, a quaint alpine town on the border of the Anza Borrego desert and the apple pie capital of the west, on Monday. It was the strongest earthquake to hit San Diego County since 2010. I bought our hilltop in early 2012.
The history of San Diego Earthquakes is more significant than I realized, dating back centuries, though it experiences fewer major events than other parts of Southern California. The first recorded earthquake in the San Diego region struck on November 22, 1800. This quake, believed to have a 6.5 magnitude, occurred on the Rose Canyon fault offshore from Oceanside and cracked adobe walls at the missions of San Diego de Alcala and San Juan Capistrano. Another earthquake damaged the San Diego Mission church on May 25, 1803. On December 8, 1812, a large earthquake with an estimated magnitude of 6.9 or larger hit Southern California, destroying a church and killing forty people attending services at the San Juan Capistrano Mission.
A magnitude 6.0 earthquake hit the San Diego region on May 27, 1862, centered on the Rose Canyon or Coronado Band faults. This quake cracked adobe buildings in Old Town and damaged the Point Loma lighthouse. Then on October 23, 1894, an earthquake with an estimated magnitude of 5.75 hit east of San Diego in the backcountry.
Flash forward a century and on June 15, 2004, a magnitude 5.2 earthquake struck off the coast of Baja California. This was the largest quake felt in San Diego in nearly two decades, though there were no reports of injuries or significant damage. A magnitude 3.9 temblor centered in Jamul was felt throughout the county on April 12, 2005, but caused little damage. On June 12, 2005, a magnitude 5.6 earthquake centered near Anza (just north of the San Diego County line) shook Southern California and cracked the wall and foundation of a North County fire station.
A 5.9 magnitude earthquake centered about 100 miles east of San Diego was felt from Los Angeles to San Diego to Las Vegas on December 30, 2009. So, there is history of earth tremors way down here away from that fabled San Andreas Fault (which runs far to the East).
Unlike other parts of Southern California, San Diego County does not have the same history of frequent earthquakes. The Rose Canyon Fault, the only major active earthquake fault in urban San Diego, has not produced a major earthquake since before European settlers arrived in the area. However, it is considered active by the State as it has had earthquakes in the last 11,000 years. Most people in San Diego County live less than 15 miles from a fault that can have a damaging earthquake, such as the Rose Canyon fault along the coast and beneath downtown San Diego, and the Elsinore and San Jacinto faults that cut through East County. The proximity of the Rose Canyon fault to the city center and main economic hubs means a major earthquake could potentially put the entire area on hold for months or years, with ground shaking from such an event likely to cause damage throughout the county. Based on data from the past 55 years and earthquake archives back to 1900, San Diego experiences about 8,600 quakes on average per year, though most are too small to be felt. The area has had at least 14 quakes above magnitude 6 since 1900, suggesting larger earthquakes occur approximately every 5 to 10 years on average. This history shows that while San Diego may experience fewer major earthquakes than other parts of California, the region remains at significant seismic risk, particularly from the Rose Canyon fault system that runs through the heart of the city.
When I bought this hilltop 13 years ago, I received the requisite report on earthquake, seismic, wildfire, flood and mudslide risk. What’s the difference between earthquake and seismic? The difference involves important distinctions in how we understand and prepare for earthquake hazards. An earthquake is simply the physical event – the sudden release of energy in the Earth’s crust that creates seismic waves. It’s characterized by its magnitude (energy released), depth, location, and other physical parameters. Seismic risk, on the other hand, is a more comprehensive concept that combines three key elements. There’s seismic hazard – The probability of experiencing earthquake ground shaking of various intensities in a specific location over a certain time period. This is based on geological factors like proximity to fault lines, soil conditions, and historical earthquake patterns. There’s seismic exposure – The people, buildings, infrastructure, and assets that could potentially be affected by earthquakes in that area. And then there’s vulnerability – How susceptible these exposed elements are to damage when subjected to different levels of ground shaking, which depends on building design, construction quality, age, and other factors. So while an earthquake is a natural phenomenon, seismic risk represents the potential for loss (human, economic, structural) resulting from earthquakes. This is why two areas might experience identical earthquakes but have vastly different outcomes – their seismic risk profiles differ based on their exposure and vulnerability factors. Seismic risk assessment is crucial for developing effective mitigation strategies, building codes, insurance policies, and emergency response plans tailored to specific communities.
What I’ve learned now is that while history shows that we here on this hilltop have earthquake risk, the North County area where we’re located actually has pretty low seismic risk. I catch shit regularly from relatives who live in San Diego proper, saying that we don’t actually live in San Diego. I generally push back on that and find it a tad offensive. When asked by people during our travels about where we live, I usually just say San Diego because that’s easier. If pushed for a specific area where we live, I say, “No, we don’t live in La Jolla, Rancho Santa Fe or Del Mar, we live in North County”. I used to say Escondido, but that’s like a New York Metro area person saying they live in Newark. It seems a bit gritty. While I used to like that feel, my neighbors on this hilltop prefer to say they live in Hidden Meadows, which we almost, but not quite, do. That’s why I’ve reverted to saying North County, which is generally understood in this area and to outsiders sounds more rural and horsey. I’m no fan of horses, but I’m willing to be lumped with them to stay out of arguments with San Diego proper folks and yet still avoid being part of the land of pick-ups in San Diego (even though I love my pick-up!).
Did you see the You-Tube video of the elephants forming the alert circle during Monday’s 5.2 earthquake? That happened at the Safari Park here in North County. I may not relate to horses, but who doesn’t love elephants. I am now one with my elephant brothers. I will stand and face the rolling thunder and declare that ain’t no seismic risk gonna harm us elephants up here in North County.