Risk is not an exact science, but with enough information and statistical data we can pinpoint the types of structures most likely to suffer damage in an earthquake – and where they are.
What earthquake threats does the Southern Cities region face? Let’s start with location: Long Beach in 1933 suffered one of the worst earthquakes in California history. The Newport Inglewood, Los Alamitos, Palos Verdes, and Cabrillo earthquake faults run directly underneath the region – slicing their way through Signal Hill, Palos Verdes Hills, underneath the harbor, and into Inglewood. This area is sandwiched between two other major threats, the Whittier and San Pedro Basin faults.
A recent study by Harvard University suggests the Palos Verdes fault could trigger a devastating earthquake of up to 7.8 magnitude — similar in scale to one that could be unleashed by the menacing San Andreas. This Palos Verdes fault line runs directly underneath the Palos Verdes Peninsula, and though mostly underwater, sits under places like Rancho Palos Verdes, Rolling Hills Estates and the Long Beach and Los Angeles Harbors. The nearly 70 mile menace stretches from Dana Point to the Santa Monica Bay.
According to the study, the fault may actually be made up of an interconnected series of smaller faults that could produce a massive quake, bigger than the deadly and destructive 6.7 magnitude earthquake that hit Northridge in 1997.
And lurking just beneath the harbor in Long Beach is a newly awakened giant: the Wilmington Blind-Thrust fault. While long dormant, this fault has recently shown new activity that could spark a destructive 6.4-magnitude quake locally, or trigger the nearby San Andreas to produce an even larger temblor reaching in the 7 magnitudes.
A series of these “sleeping giant” faults was recently discovered in the Long Beach/Seal Beach region – thankfully without having unleashed their destructive force. The faults form a ladder-like grid over the Harbor area and inland to Cal State Long Beach, with a series of rungs crossing at the Los Alamitos Channel and north up to Pacific Coast Highway.
Liquifaction also threatens the area. Loosely packed, water-logged sediments typical of the region’s lower-lying areas can intensify the risk by adding to the motion of a quake. Liquefaction amplifies the impacts of seismic waves produced during an earthquake, causing the ground to react like Jello-O: jiggling, undulating, and putting the structures built upon it in increased jeopardy.
The United States Geological Survey has published an interactive map online, enabling the public to search by property address to determine the earthquake risks associated with specific land parcels. Properties located on or near a fault or liquefaction zone are particularly at risk of damage in an earthquake. Visit the California Earthquake Hazards Zone Application Map at https://maps.conservation.ca.gov/cgs/EQZApp/app/.
Building type and age is another major consideration in determining risk. Certain construction designs, when built prior to current safety codes, have been proven to be extremely vulnerable to damage under seismic shaking. The primary and most common of these structures include:
- Pre-1978 soft-story structures (featuring parking on the ground floor with units built above)
- Pre-1933 unreinforced masonry buildings
- Pre-1980 concrete tilt-up buildings
- Pre-1977 non-ductile concrete structures
- Pre-1996 steel moment frame buildings
Given the region’s propensity for major earthquakes, if your apartment building is the type proven to be vulnerable to earthquake damage, you should consider having an engineering study done to determine the extent of work that should be done – so you can start planning to protect yourself in the future. To learn more, call Optimum Seismic at 833-978-7664 to arrange a complimentary evaluation of your building.