Despite Recent Earthquakes, California Still in 'Earthquake Drought' | Nation World

LOS ANGELES – Despite an unusually high number of modest earthquakes this year in Southern California, the state as a whole is still suffering from a drought of major quakes.

No major destructive earthquakes have occurred beneath California's oldest and most populous cities in the past 30 years, sparing places like Los Angeles, San Jose, San Francisco, Long Beach and Oakland from earthquake-related deaths and destruction.

This is in stark contrast to the previous three decades, when earthquakes in urban or mountainous areas caused catastrophic damage to urban infrastructure, collapsing highways and buildings and killing dozens of people.

“If we take the last 30 years as a definition of earthquake frequency, we underestimate the long-term frequency,” said Lucy Jones, a seismologist and research fellow at Caltech. “Since the Northridge earthquake in the Los Angeles area, we’ve had fewer earthquakes, and fewer damaging earthquakes, than the long-term frequency.”

30 years, but for how long?

Between 1964 and 1994, Los Angeles experienced two major earthquakes that struck the San Fernando Valley: the 6.6-magnitude Sylmar earthquake in 1971, which killed 64 people; and the 6.7-magnitude Northridge earthquake in 1994, which killed about 60 people. The Northridge quake caused $20 billion in damage and an additional $40 billion or more in economic losses—the costliest earthquake disaster in U.S. history, according to the California Geological Survey.

Scientists warn that these quakes are relatively mild compared to what can happen. No one alive today has experienced the kind of seismic force that California’s first inhabitants faced more than a century ago. In 1906, a 7.9-magnitude quake ruptured 300 miles of the San Andreas Fault, from Humboldt County to San Benito County, destroying much of San Francisco.

The last major earthquake in Southern California was in 1857, when a magnitude 7.9 quake ruptured 225 miles of the San Andreas Fault, between Monterey and San Bernardino counties. A hypothetical future magnitude 7.8 earthquake on the southern San Andreas Fault, from the Mexican border to Los Angeles County, could kill 1,800 people and injure nearly 50,000, according to the U.S. Geological Survey’s “ShakeOut” scenario.

This scenario is expected to result in the deadliest earthquake in modern Southern California history, with more than 1,000 deaths possible in Los Angeles County alone.

A 7.8-magnitude Shakeout quake would be more than 12 times stronger than the Northridge quake as measured by a seismograph. But the most important comparison is that Shakeout would be 45 times stronger than Northridge in terms of energy release. The 1994 quake produced shaking that lasted between seven and 15 seconds; many buildings would experience shaking that lasted about two minutes in a Shakeout quake, according to the U.S. Geological Survey.

There is now an entire generation of Californians who grew up without experiencing the devastating earthquakes of the 1980s and 1990s, even smaller ones that caused localized damage, like the 5.9-magnitude Whittier Narrows earthquake, centered in the San Gabriel Valley, which killed eight people in 1987.

There have certainly been a handful of earthquakes of magnitude 6 or greater in the past three decades that have damaged California. Humboldt County experienced them in 2010 and 2022; the Mojave Desert in 1999 and 2019; Napa County in 2014; Imperial County in 2010, the result of a quake centered in Baja California; and San Luis Obispo County in 2003.

The quakes were the most significant of 12 earthquakes of magnitude 6 or greater that have struck California and Nevada in the past 30 years.

But that number is less than half of the 28 earthquakes of magnitude 6 or greater during the previous 30 years, between 1964 and 1994.

unfinished business

The earthquakes that struck California in the 1980s and 1990s were a new wake-up call about California’s seismic vulnerabilities. Earlier earthquakes—the 6.4-magnitude Long Beach earthquake of 1933, centered just off the coast of Huntington Beach, and the Sylmar earthquake—led to changes in building codes and a better understanding of seismic risks.

Officials responded to the earthquakes of 1989 and 1994 with an unprecedented seismic safety campaign that redesigned California's highways and bridges and raised public awareness of the financial and personal risks.

But our progress began about a decade ago. In 2013, San Francisco ordered the repair of low-rise apartments, which were vulnerable to collapse because their upper floors were supported by thin columns above carports or garages.

Los Angeles followed suit in 2015, also requiring the retrofitting of “non-ductile” or brittle concrete buildings. Cities in Southern California that have recently passed retrofitting laws include Torrance, Pasadena, Santa Monica, Culver City, West Hollywood and Beverly Hills. In Northern California, they include Oakland, Berkeley, Fremont and Mill Valley.

But not all of these cities have ordered the retrofitting of every type of building that worries structural engineers. And many others have done nothing for decades to retrofit or demolish at-risk buildings. Experts say much more needs to be done, and they worry that the lack of a major urban earthquake since 1994 could lead people to forget.

Apartment owners who fail to retrofit their earthquake-prone buildings risk total loss. About 200 single-story apartment buildings in the Los Angeles area were seriously damaged or destroyed during the Northridge quake. In one of those buildings, the Northridge Meadows complex, 16 people died when the ground floor collapsed. Experts warn that the collapse of many of these buildings in a future quake would lead to increased homelessness and threaten the limited supply of affordable housing, compromising the community’s ability to recover after the quake subsides.

Some cities remain decades behind in seismic safety laws compared to other regions, which began voting decades ago on whether to order the rehabilitation or demolition of century-old brick buildings. Of particular concern is the Inland Empire, which straddles the San Andreas Fault. A 2018 Times investigation reported how hundreds of old brick buildings in more than a dozen Inland Empire cities remained unrepaired despite decades of warnings.

Government officials are also taking steps to encourage single-family homeowners to voluntarily renovate their homes. Relatively simple repairs to protect homes can save owners hundreds of thousands of dollars in damage after an earthquake.

High seismic activity in 2024

For those who may be wondering if Southern California is experiencing more earthquakes than usual, it's not just a myth.

The 4.7-magnitude quake north of Malibu on Thursday was the 14th so far this year in Southern California to have had at least one quake of magnitude 4 or greater, Jones said. That broke a record set in the past 65 years.

During that time period in Southern California, there were an average of eight to 10 independent earthquake series that included at least one earthquake of magnitude 4 or greater. In some years, there were only one or two such series. The previous record was in 1988, when there were 13 such series, Jones said.

Scientists say seismic activity doesn't necessarily indicate a major, destructive earthquake is coming. Researchers have proposed conflicting theories — some say seismic activity increases in an area before a major quake, others say seismic activity decreases before a major quake.

So the recent activity doesn't offer any hints about when the next big, devastating earthquake might strike, according to USGS seismologist Susan Hogg.

“Yes, this year is more active than it has been in the past,” Jones said, but added, “We can't say yet whether it's statistically significant to see this or not.”

The recent earthquakes “are a really good reminder that the calm of the last two decades is not the picture we expect in the long term, and we need to be prepared,” Jones said.

Why do we talk more about earthquakes?

Some people have noted that we may be talking about minor earthquakes more than we used to. This is probably due to a number of reasons — including the rise of the Internet and social media, which make it very easy even for people who have never felt a particular earthquake to talk about it.

“Decades ago, if you felt something, you talked about it with your friends,” Jones says. Now, even people who don’t feel it can talk about how they don’t feel it.

“Today it is very easy to get information,” she added.

Processing seismic data has also become much faster these days. Decades ago, determining the size and location of an earthquake was a time-consuming process.

“At that time, in order to pinpoint where an earthquake occurred, we had to have a seismologist come into the lab and look, pull up the records and calculate them,” Jones said.

At the time, seismologists relied on an alarm system operated from six stations across Southern California that drew graphs etched with a mechanical pen, which would ring when at least two of them went out of range, indicating a magnitude 4 or greater earthquake. If the alarm went off outside business hours, someone would have to call a list of seismologists until someone agreed to come.

This means that earthquakes of magnitude 3 or less were not a priority for relatively rapid analysis.

So it took about an hour to get a preliminary location and magnitude of the 1987 Whittier Narrows quake, Jones said, and nearly three hours before she could officially begin talking to reporters about more details. Jones and other seismologists had to sift through paper records, measure them by hand, and first guess the quake’s magnitude.

“Shake maps”—maps that can measure the intensity of vibrations felt by people everywhere—were not available nearly as quickly as they are today. Making them required sending out surveys or getting records of strong movement. “We had to go take film slides and process them, so it took about a month or two,” Jones says.

Compare that to Thursday, when some people got an early estimate of the quake’s strength on an earthquake early warning app seconds before they felt shaking, and Jones was available on a Zoom conference call with reporters just minutes after the quake.

“Very good reminder”

Risks surround us everywhere.

Consider the Puente Hills fault system, which has been linked to several earthquakes this year centered in El Sereno, a neighborhood on the east side of Los Angeles. In 2005, the U.S. Geological Survey and the Southern California Earthquake Center said that a magnitude 7.5 quake on this fault system, which runs beneath downtown and a large swath of southeastern Los Angeles County, the San Gabriel Valley and northern Orange County, could kill as many as 18,000 people and cause $250 billion in damage. Such a quake would be 15 times more powerful than the Northridge quake in terms of energy release. It is impossible to say when such a large quake might occur.

The east-west faults that ran near Thursday’s Malibu quake also pose a threat. Earthquakes in that area can reach magnitude 8, which is “pretty much standard anywhere in California,” said Morgan Page, a geophysicist with the U.S. Geological Survey. That’s because individual faults can connect with other faults in the same seismic event to create a larger quake.

Officials fear a major quake could cut off vital utilities and communications in Southern California for days, if not weeks. Among the vulnerable spots is the Cajon Pass, a narrow mountain pass where the San Andreas Fault intersects with flammable natural gas and oil pipelines, power lines, railroad tracks and Interstate 15 north of San Bernardino. Earthquakes could also cripple vital water supplies to Los Angeles.

The Malibu quake provides another reason to prepare, said Hogg, a seismologist with the USGS.

“It's a very good reminder to people that we live in earthquake country, and we need to take steps that will help keep us all safe in the event of a larger earthquake,” she said.

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