Earlier predictions of Southern California’s earthquake risk were dire enough as many as 1,800 deaths, 50,000 injuries, and $200 billion in damage with long-lasting social and economic impacts.
New figures from the U.S. Geological Survey are significantly worse: more than 1,000 dead in Los Angeles alone; major transportation corridors destroyed; water supplies threatened, and between 500,000 and 1 million people displaced from their homes.
Every five years, the USGS releases an updated seismic hazard map showing areas of high-vulnerability to earthquakes. The report factors in recent seismic activity, including data from the recent Ridgecrest earthquakes, along with new information on building and soil types which are incorporated into hazard models used to project anticipated loss for a region.
Another factor in determining hazard risk, is the growth of urban centers in the Bay Area and Southern California.
The denser the population, the greater the risk for death, injury and economic loss.
Local threats calling for mandatory earthquake retrofitting
The Newport-Inglewood faults remains a serious risk to residents of the Long Beach area, which suffered a devastating earthquake in 1933. The devastation from that quake led to legislation requiring the seismic retrofit of all public school buildings in the state.
The 6.4-magnitude jolt led to 120 deaths, 500 injuries and some 34 terrifying aftershocks in the six hours following the initial jolt. Some $50 million in damage – $921 million in today’s dollars – was reported in Long Beach, Huntington Park, Compton and surrounding areas.
Untold numbers of children were spared from death or injury because the quake happened around dinner time. Had it struck just a few hours earlier, the more than 120 schools that were destroyed or severely damaged in the quake – facades crumbed, entire floors pancaked on top of each other – would have certainly harmed many hundreds more than the lives taken that day.
Precisely how vulnerable Long Beach is to a major earthquake is still to be determined, as the city awaits completion of a seismic resiliency safety database requested early last year to identify the city’s most vulnerable structures.
Many of the city’s structures are known to be older, built before modern building codes.
Is your building at risk?
Seismologists and structural engineers have identified certain buildings types most likely to sustain damage in a major earthquake. These include:
- Soft-story built before 1978: Structures with parking on the ground floor and units built above are prone to collapse during major earthquakes.
- Unreinforced Masonry built before 1975: The facades of these buildings frequently collapse in a quake.
- Concrete Tilt-up’s built before 1994: Weak connections can fail and cause walls to pull apart from the roof, presenting a collapse hazard.
- Non-Ductile Concrete built before 1977: Limited lateral resisting capacity makes these structures brittle.
- Steel Moment Frame built before 1996: These buildings can sustain brittle fracturing of the steel frames at welded joints between beams and columns.
A detailed USGS scientific assessment of potential damage from a magnitude-7.8 San Andreas earthquake in Southern California estimated that 300,000 structures would be damaged. That’s one in every 16 buildings in our region.
Will yours be among them? Most earthquakes are small, virtually imperceptible, but scientists universally agree that we are long overdue for “The Big One.” It’s just a matter of time.