Seismologists are closely monitoring California’s fault lines as concerns grow about the possibility that the “Big One” could happen soon.
The “Big One” refers to a massive earthquake that could occur along the San Andreas Fault, one of the state’s most significant and active fault lines. Scientists predict that this earthquake could reach a magnitude of 7.8 or higher, causing widespread destruction across Southern California or the San Francisco Bay Area depending on the rupture location.
Why It Matters
The possibility of a major earthquake in California is a significant concern due to the state’s location along active fault lines. With the buildup of seismic stress along the San Andreas Fault and smaller local faults, experts warn that the risk of a large-scale earthquake is high, particularly in the southern regions of the Golden State.
The potential for catastrophic damage—affecting infrastructure, homes, and lives—makes it crucial for California to be prepared.
What To Know
California has been rocked by at least nine earthquakes since Thursday, raising fears that the “Big One” is near.
The strongest recent earthquake to shake California was a 4.3 magnitude that struck 6 miles north-northwest of Avenal at approximately 4:17 p.m. on February 13, according to the United States Geological Survey (USGS).
Three earthquakes were also recorded 1 mile from Hayward in California’s Bay Area on Thursday afternoon. Two of those earthquakes occurred within two minutes of each other. All three occurred along the Hayward fault line, which USGS notes is an active fault in the San Francisco Bay region. They had magnitudes of 3.2, 3.3 and 2.6 respectively.
The Hayward Fault runs along the foot of the East Bay Hills. The last major earthquake hit on October 21, 1868, measuring a 6.8 magnitude.
Another 2.5 magnitude earthquake also struck 2 miles off of Pleasant Hill in the Bay Area at approximately 4:45 p.m. local time on Thursday afternoon, according to USGS.
Meanwhile, a 2.9 magnitude earthquake struck 10 miles west-southwest of Petrolia in Northern California at around 11:40 a.m. on Thursday morning.
Three earthquakes then hit California on Friday, including a 3.2 magnitude quake 5 miles from The Geysers, which happened at around 10:20 a.m. local time. Another struck five hours later, at 3:42 p.m., 2 miles southwest of Anderson Springs. It had a 2.7 magnitude.
The latest quake to hit the state was recorded in the Malibu area late Friday at approximately 11:44 p.m. and had a 3.7 magnitude. According to USGS, the quake was felt as far as 50 miles away in Los Angeles County, in Long Beach, Porter Ranch and Whittier. It was also felt 30 miles away in multiple cities in Ventura County, including Thousand Oaks, Port Hueneme, Oxnard, Camarillo and Simi Valley.
Hundreds reported feeling the seismic events, according to the USGS, but no damage was reported from the earthquakes. Nonetheless, experts now fear that a major seismic event is on the way, especially after four earthquakes struck the southern portions of the state within 24 hours earlier this week, some along the famous San Andreas Fault, where the “Big One” expected to occur.
“Since it has been more than 144 years since the last major earthquake, the clock is ticking,” researchers at the University of California, Berkeley, stated in 2018. “It is very likely that the Hayward fault will rupture and produce a significant earthquake within the next 30 years.”
Experts told Newsweek that California’s next major seismic event is most likely to occur in the southern part of the state.
“Overall, Southern California has a 36% chance of a M7.5 or greater earthquake in the next 30 years,” Elizabeth Cochran with the USGS Earthquake Science Center said. “California is known as ‘earthquake country’ and residents should be aware of earthquake hazards and take steps to mitigate their personal risk.”
She added that “temporary increases or decreases in seismicity are normal and expected.”
Professor Jonathan Stewart of the UCLA Samueli School of Engineering, agreed, telling Newsweek: “The Big One in California lacks a specific scientific definition, but is generally considered to be a magnitude 8 (+/-) event on the plate boundary fault, which is the San Andreas Fault. The stress on this fault builds up with time since the last major earthquake. The dates of those last major events are 1906 for the northern portion of the fault (north of Parkfield, including San Francisco), 1857 Fort Tejon earthquake (Parkfield south to Cajon Pass), and a 1690 for the southern-most portion of the fault.”
He added: “Given that stress builds up with time, we can expect that the southern segment is most likely to produce the next large event.”
A potential magnitude 8 quake would wreak havoc upon the state’s most populated cities, causing roughly 1,800 deaths, 50,000 injuries, and $200 billion in damage, according to estimates by the California Earthquake Authority (CEA).
However, Stuart said the risk of the “Big One” occurring “is not appreciably higher now that it was a few years ago.”
“The stress accumulates over longer time scales,” he said. Stuart added that we should “not lose sight of the significant damage potential of smaller, not plate boundary, faults closer to and within the greater Los Angeles metropolitan region,” not just the large plate boundary faults like the San Andreas Fault.
“The two most recent damaging earthquakes in 1971 and 1994 were on smaller faults in the San Fernando Valley,” he said.
Los Angeles has been no stranger to natural disasters, having been ravaged by wildfires last month that burned over 47,900 acres, destroyed more than 16,250 homes and businesses, and killed 29 people.
Since then, several California officials, including Los Angeles Mayor Karen Bass and Los Angeles Fire Department (LAFD) Chief Kristin Crowley and California Governor Gavin Newsom have faced criticism for their response to the wildfires after some hydrants went dry as firefighters tried to battle the blazes. California officials have said that it was because of the high local demand.
Newsom is now facing a recall petition to remove him from his position which accuses him of “gross mismanagement during the Los Angeles County fires,” saying that “inadequate resources and delayed responses left communities devastated.” In response, Nathan Click, a spokesperson for Newsom, previously told Newsweek: “Governor Newsom is focused on marshalling resources for fire recovery—not politics.”
However, the political fallout from the wildfires has put California’s disaster response system in the spotlight.
Stuart told Newsweek that California has made “significant progress” in reducing its seismic risk.
“We’ve made significant progress in California to reduce seismic risk, including retrofit programs for highway bridges, initiatives to harden the state’s hospitals and health clinics, and mandatory retrofit ordinances for particularly vulnerable building structures in several California cites (e.g., Los Angeles, San Francisco),” he said.
The state, through the Office of Statewide Health Planning and Development (OSHPD), mandates that health care facilities meet strict seismic safety standards. Additionally, cities like Los Angeles and San Francisco have introduced mandatory retrofit ordinances for vulnerable structures such as unreinforced masonry buildings (URMs) and soft-story buildings to reduce earthquake risks.
But despite these measures being put in place, Stuart noted that California still has a long way to go in terms of improving its disaster response system.
“The list of challenges remains long,” he said. “Some particularly significant ongoing risks are related to water transmission and distribution systems, other lifelines, and structures not yet investigated or retrofitted. Maintaining focus on these problems in the public policy sphere is challenging given the significant time since the last event in 1994 that produced significant damage in a California urban center. Addressing the technical and policy-related issues to reduce seismic risks over time remains an active area of research and professional work.”
What Happens Next?
It is unclear when, or if, the “Big One” will hit California. For now, it is more likely the recent earthquakes in California will result in smaller aftershocks. If more occur, they will likely be reported on USGS’ latest quakes webpage.
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