4.4 earthquake was centered on notorious L.A. fault
system
By Rong-Gong Lin II, Nathan Solis, Howard Blume and
Karen Garcia
Aug. 12, 2024 Updated 6:08 PM PT
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The magnitude 4.4 earthquake that rattled Los Angeles
on Monday was centered within one of the region’s most
potentially destructive fault systems, one capable of
producing a magnitude 7.5 earthquake under the heart of
the region.
Seismologist Lucy Jones, a Caltech research associate,
said the earthquake, centered in the Eastside
neighborhood of El Sereno, occurred on the Puente Hills
thrust fault system. It’s the same overall fault
network that produced the 1987 Whittier Narrows
magnitude 5.9 earthquake — which killed eight people
and caused some $358 million in damage.
A magnitude 7.5 quake in the Puente Hills thrust fault
system — which runs under highly populated areas of
L.A. and Orange counties — could kill 3,000 to 18,000
people, according to the U.S. Geological Survey and
Southern California Earthquake Center. The economic
loss could be up to $252 billion, which could be the
costliest disaster in U.S. history.
That’s worse than the hypothetical death toll of 1,800
people from a plausible magnitude 7.8 earthquake that
begins on the southern San Andreas fault near the
Mexican border and unzips all the way to the mountains
of L.A. County.
“It’s a reminder that this is actually our most
dangerous fault,” Jones said.
A big earthquake on the San Andreas fault comes every
century or so, and one within the Puente Hills thrust
fault system comes every few thousand years. But if a
magnitude 7.5 earthquake in the Puente Hills thrust
fault system comes in our lifetime, it would be far
worse for the L.A. area than a big one on the San
Andreas.
The Puente Hills thrust is a complex fault system with
many intersecting strands, Jones said. It’s possible
that the fault strand that ruptured in Monday’s quake
itself is technically small and unnamed, Jones said.
Whatever it is, Monday’s quake is associated with the
greater Puente Hills thrust fault system.
Monday’s earthquake, centered about 1,100 feet
southwest of the intersection of Huntington Drive and
Eastern Avenue, occurred in the same general area of a
pair of earthquakes in early June — a magnitude 3.4 on
June 2 and a magnitude 2.8 on June 4, also associated
with the Puente Hills thrust fault system. There was
also a magnitude 2.9 earthquake in the same area on
June 24.
“All of these earthquakes are closely spaced in three
dimensions, just beneath the main Puente Hills thrust
[fault] plane,” USC earth sciences professor James
Dolan said. “They’re all associated with the same
cluster of small events.
“But the key thing is, they are very small events.
These are very small earthquakes that don’t necessarily
mean anything in terms of potentially being the
harbinger of a future large magnitude earthquake on the
Puente Hills thrust,” Dolan said.
Still, people should heed the lessons from this small
quake, Dolan said, and take action to prepare for
future ones, such as buying extra water for their home
and workplace, and securing spaces like fastening
bookshelves to walls. “If it inspires even a few people
to do that ... that’s a good thing for L.A.,” Dolan
said.
“People really need to be ready for a very, very large
earthquake, or earthquakes, in L.A.’s future. It’s
going to happen. We don’t know when. We don’t know
exactly which fault is going to generate those
earthquakes, but they are going to happen,” Dolan said.
Monday’s earthquake is also a reminder of how, while
some large cities in the region, such as L.A., have
taken action to order earthquake retrofits of certain
types of buildings, most others have not.
One vulnerable type of building that has received
considerable attention from some cities are apartment
buildings with flimsy first stories, held up by skinny
poles atop carports that can collapse when shaken.
While cities such as Los Angeles, Torrance, Pasadena,
Santa Monica, Culver City, West Hollywood and Beverly
Hills have ordered such buildings to be retrofitted,
most others in the region have not, including areas in
the San Gabriel Valley and southeast L.A. County shaken
up by Monday’s temblor.
“This is something that not only kills people, as we
saw in ’94, but it also leaves people homeless,” Jones
said, referring to the collapse of the Northridge
Meadows apartment complex during a magnitude 6.7
earthquake three decades ago. “I would strongly
encourage anybody ... that has an influence on this to
look at getting more of those buildings retrofitted,
because we can’t afford to lose that housing when a
bigger earthquake comes through.”
Another building at high risk are “non-ductile”
concrete buildings, which, as recent earthquakes in
Mexico, Turkey and Syria have shown, can cause large
numbers of deaths if the flaws are not resolved.
The Puente Hills thrust fault system is especially
worrisome because of what’s on top of it — downtown Los
Angeles, which has many old and unretrofitted
buildings, as well as broad swaths of southeast L.A.
County, the San Gabriel Valley and northern Orange
County.
Monday’s earthquake was notable for stronger shaking
occurring southwest of the epicenter. One explanation
for that is those locations happen to sit on thicker
piles of sediments — sand, gravel and soils — and as a
result, it’s going to shake more there than for people
on top of bedrock, Dolan said.
That would explain why many felt scary shaking on top
of the Los Angeles Basin, a 6-mile-deep, bathtub-shaped
hole in the underlying bedrock filled with weak sand
and gravel eroded from the mountains and forming the
flat land where millions of people live. The area
stretches from Beverly Hills through southeast L.A.
County and into northern Orange County.
Mike Martinez can tell you what it feels like to be at
the epicenter of a moderate earthquake. Martinez is a
painter at Frank’s Auto Body & Paint at Huntington
Drive and Collis Avenue, which is exactly where the
underground fault ruptured.
Martinez remember a loud, sharp blow and then a few
residual vibrations. Everything was over in a few
seconds.
“Some other times, it starts low, then increases,”
Martinez said. “This hit like a truck.”
What was going through his mind?
“The Big One is coming up,” Martinez said.
The northwest corner of that intersection is occupied
by an auto plaza with three shops. Next door, Eduard
Balasian, the owner of AA Auto & Muffler, recalled that
all the employees from all the shops ran outside into
the parking lot.
Products and supplies fell off shelves, but that was
the worst of it. Nothing spilled or broke open.
“We are lucky that a car wasn’t on a lift,” he said.
The initial jolt, he said, was violent enough to have
knocked a car off the service lift, imperiling anyone
working directly below. “We are lucky.”
The earthquake caused a water pipe to burst at Pasadena
City Hall, where water leaked for about an hour before
it was turned off, city spokesperson Lisa Derderian
said.
It also caused an issue with elevators at the building,
and an employee was stuck in one of the cars for about
20 minutes before being let out. The elevators will be
closed until they can be repaired.
The fire department is conducting surveys around the
city, and an engineer is being sent to the Rose Bowl as
a precaution to assess for any issues.
Darlene Hampton, a senior office assistant in the
Pasadena city manager’s office, was helping a resident
at City Hall when the shaking started.
“She was having a little bad day,” Hampton said about
the resident. “I was able to calm her down, and we just
said, ‘Everything’s going to work out, right?’ And then
the earthquake hit. But we were doing a little prayer
too.”
All employees and customers were able to leave the
building safely, Hampton said, and wait outside until
the fire department arrived.
“The funny thing is, as she’s going out the door, I
said, ‘You see how quickly God works?’ ”
The shaking brought a short jolt of up-and-down motion
that knocked shampoo bottles off the shelf at the
Target in Alhambra, as well as the “shredded cheese”
sign off a refrigerated aisle, and shoppers started
calling loved ones to see whether they were OK.
In Highland Park, windows rattled and dogs barked, and
coffee spilled off a table. Elsewhere in Alhambra,
photos were knocked off the shelf, drawers opened and
shoes were thrown from a rack.
The temblor struck at 12:20 p.m. The preliminary
epicenter was in El Sereno, about 1,000 feet southwest
of Huntington Drive and Collis Avenue.
The strongest shaking was considered “moderate,” or
Level 5 on the Modified Mercalli Intensity Scale, where
the shaking was felt by nearly everyone and capable of
overturning unstable objects. Moderate shaking was
experienced in downtown Los Angeles, South Pasadena,
Highland Park, Mount Washington, Alhambra, Monterey
Park, Boyle Heights, East L.A., South L.A., Huntington
Park, Bell, Maywood, Bell Gardens, Cudahy and South
Gate, according to the USGS.
People across the region felt shaking strong enough to
knock items from shelves, including a bottle of bay
leaves in Koreatown. The seventh floor of The Times’
headquarters in El Segundo, near Los Angeles
International Airport, swayed as lights flickered and
televisions that hang on walls swayed. In the Los
Feliz-East Hollywood area, car alarms sounded, candles
were knocked off tables and people exclaimed, “That was
scary!” Windows at businesses in Los Feliz shook.
In Silver Lake, a loud, sharp jolt lasted five to 10
seconds, shaking the exhaust hood in a kitchen. Windows
rattled and the walls shook at one home in Atwater
Village.
In Arcadia, people felt both a shaking and rolling
motion, lasting about 20 seconds or so — like a nearby
train rolling through. One person in South Pasadena
felt a very sharp, loud jolt, sending her under the
table, but nothing broke or fell. A person in Mid-City
felt a sizable jolt on the ground floor.
Dozens of Inglewood community members and teachers
crowded outside Morningside High School, just a mile
south of SoFi Stadium, to eat lunch after an event
attended by Jimmy Iovine, co-founder of Interscope
Records, when the ground rumbled for a full second.
“That a quake?” a teacher asked a colleague.
At Fatty Mart convenience store in Mar Vista, people in
the seating area simply stared at one another when the
shaking arrived. Two continued munching on their food,
while another kept working at his computer.
“Is this an earthquake?” someone said five seconds into
the shaking, which lasted for 10 or 15 seconds longer.
Many Southern California residents received alerts on
their phones warning the quake was coming, another win
for the region’s earthquake early warning system. Some
got the warning just after the jolt hit, as they were
quite close to the epicenter.
There were no reports of damage, the fire departments
for the city and county of Los Angeles said. The South
Pasadena Police Department has not received any calls
for service, other than multiple reports of home alarms
being set off by the earthquake.
Anthony Montiel, facility director with the Lincoln
Heights Senior Center, said there were no reports of
any injuries or emergency calls for assistance.
He said for the most part, everyone kept calm — save
for himself.
“I’m more scared than anyone else, with them being
seniors and having more life experience,” Montiel said
with a laugh.
“It felt like a truck hit the building. It was like a
strong jolt that lasted a few seconds, and nothing like
a rolling earthquake,” he added.
When a quake struck Bakersfield last week, millions got
the alert.
According to the U.S. Geological Survey, Monday’s
temblor was felt across the L.A. basin and as far away
as San Diego and Ventura.
Those who have iPhones can get earthquake early
warnings by downloading the free MyShake app, developed
by UC Berkeley and provided in partnership with the
California Governor’s Office of Emergency Services,
which alerts users in California, Oregon and
Washington. San Diego County also offers the free SD
Emergency app, which includes the ShakeReadySD
earthquake early-warning tool.
People who don’t have smartphones or haven’t installed
early-warning apps can still get quake alerts on their
cellphones — but only for those in which a higher
magnitude or higher level of shaking is projected at
their location. Those alerts are sent through the
Wireless Emergency Alert system, similar to Amber
Alerts.
The shaking was light enough for some to make jokes.
In a downtown L.A. courtroom, a fire alarm went off
multiple times a couple of hours after the shaking.
“It could be a delayed reaction to the earthquake?”
said Judge Sam Ohta from the ninth floor of the Clara
Shortridge Foltz Criminal Justice Center, which shook
for several seconds around lunchtime. “1971 building.”
“The county’s early warning system,” someone joked.
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