‘We’ve been lucky’: Recent quake highlights need for retrofits of Pasadena’s Central Library, experts say

As Pasadena’s beloved Public Library marks its 140 years of service this year, the Central Library’s resilience is once again being tested by nature.

A recent 4.4-magnitude earthquake that struck Highland Park on Aug. 12 has left its mark on the 100-year-old facility, adding two new cracks and expanding an existing one, city officials said.

These new scars are a stark reminder of the building’s vulnerability – an issue that led to its closure in 2021.

 

“The building is unreinforced masonry. It’s not up to current building code,” Pasadena’s Library Director Tim McDonald said. “The right size earthquake coming from the right direction could bring the building down. So the reason that it’s still standing is, we’ve been lucky.”

While the building is closed, staff has continued to perform essential maintenance, such as monitoring its leaky roof, McDonald said. However, the cracks will not be repaired until the retrofit project is funded and starts, when it “would be the time to address those issues”, he added. Voters will have a chance to decide on a $195 million bond for the project in the November election.

For experts monitoring the building, the damage serves as a grim reminder that even moderate-sized earthquakes can cause significant harm to such historic structures.

“What we do know is that with the kind of construction that this building has, it’s cracking in ways that it probably shouldn’t,” said Dr. Monica Kohler, a research professor of Mechanical and Civil Engineering at Caltech.

Earthquakes of this size, like the one on Aug. 12, shouldn’t cause such damage, said Kohler, who also serves on the library’s Technical Oversight Committee, formed in 2022.

“What the engineers know from inspections of the building and seeing how it was constructed, the building is responding in a brittle way,” she said. “That is when stresses or forces are applied to the building, it’s just cracking right away in ways that it shouldn’t be.”

To understand how the Central Library responds before and after retrofitting, her team installed 25 sensors throughout the building last April, Kohler said. These sensors operate around the clock, continuously recording earthquake vibrations.

The data they captured during the Aug.12 earthquake was surprising, given its relatively low amplitude, she said.

“The amplitudes aren’t huge, they’re not like the kind of amplitudes that we might expect from a magnitude 7.8 on the San Andreas Fault or a 7.5 on the Puente Hills fault system. Those are going to be much, much larger,” she said. “The fact that we saw this damage in the library from this relatively small earthquake should open up our eyes to the possibility of there being much more damage on even a moderate-sized earthquake in the future on any one of our local faults.”

“The right size earthquake coming from the right direction could bring the building down. So the reason that it’s still standing is, we’ve been lucky.” — Pasadena Library Director Tim McDonald

The Central Library was the first building constructed in the city’s Civic Center Plan. Designed by Myron Hunt in 1924 in the Spanish Colonial Revival-style, this multi-floored structure was completed in 1925 and later renovated in 1966 and 1984.

“Our older buildings were built at a time when we didn’t understand as much about how earthquakes affect buildings, and therefore, the older buildings are more likely to have structural problems,” Caltech’s Seismologist Dr. Lucy Jones said.

The Central Library is one such building. It’s constructed with unreinforced masonry walls (URMs), or thin brick walls that act as the gravity and seismic “resisting system,” city officials said. These walls lack additional column support, meaning they are not equipped to withstand the large sideways motions generated by bigger earthquakes.

As a result, there isn’t any part of the building that is more vulnerable than others, because the entire structure is made up of URMs, Kohler said.

“And so everywhere in the building we’re worried about the structural stability of the building because of the deficient nature of these walls and because of the lack of good connections between the walls and the floor slabs and the roof,” she said.

After the 1933 Long Beach earthquake led to the complete collapse of some URM buildings, building codes were updated to prohibit this type of construction.

Although Pasadena passed an ordinance in 1993 requiring all URM buildings to be retrofitted, vacated or demolished, it’s unclear why the Central Library was not identified and addressed at that time, Pasadena’s spokesperson Lisa Derderian previously said.

It wasn’t until 2021, while conducting a thorough building assessment of the Central Library in anticipation of its 100th birthday in 2027, that city officials discovered its URM structure, leading to its closure.

Besides URMs, Kohler also identified two other types of buildings that are vulnerable during earthquakes: Non-ductile concrete buildings and soft-story buildings.

Non-ductile concrete buildings are structures without sufficient rebar or internal reinforcement to allow flexibility under stress. Unlike modern buildings that can bend slightly during an earthquake, these structures are prone to brittle failure, meaning they can crack and break apart easily.

Soft-story buildings, on the other hand, have weaker first floors, often with large openings like garages or storefronts, supported by thin columns or poles. The lack of sufficient support makes them highly susceptible to collapse during seismic events.

“Anywhere where you have this kind of building in a seismically active region, you need to be concerned about how it’s going to withstand a moderate or large earthquake,” Kohler said.

But Pasadena city officials, for their part, have said they are committed to preserving and retrofitting historic buildings.

“Today, the city continues to work to preserve and retrofit historical or valued properties (private or public) for life safety reasons and the preservation of their history and architectural value,” Derderian said. “The Central Library is the focus of what we are doing today and is going before the voters.

“The opportunity to save and reopen the nearly 100-year old Central Library is now,” she continued.  “This retrofit, repair and upgrade not only provides the necessary life safety intervention into the structure for contemporary uses, but allows for the City to take it into the 21st Century, modernizing its usefulness, technology and adaptation for future generations to come, (the next 100 years) while protecting the historical and architectural integrity of the of the Central Library.”

But this focus on preservation and safety isn’t limited to the library, Jones said.

“The City Hall and Civic Auditorium, I am reasonably certain, have been retrofitted,” she said. “And City Hall, in particular, went through what’s called a base isolation procedure.”

In this procedure, the building is essentially decoupled from the ground, Jones said. It sits in a moat with rollers underneath.

“And so as the ground moves, the building with all its inertia tends to stay where it is and it can shift with respect to the ground because you’ve got this isolation system,” she said.

Pasadena City Hall — built in 1927 — was closed in 2004 for retrofitting and renovation. Three years later, staff moved back in.

In May 2019, the city adopted a mandatory seismic retrofit ordinance, which requires landlords to upgrade soft-story buildings. At the time, city staff estimated that 500 buildings containing 4,500 units in Pasadena fall under this category.

Owners have three years upon receiving the city’s notice of retrofit requirement to submit retrofit plans and obtain permits and seven years to complete final construction, according to a staff report. The time to submit plans and obtain permits was later extended to four years during COVID.

“That’s an issue that relatively few jurisdictions in Los Angeles County have undertaken,” Jones said.

And if the recent earthquake is any indication, it serves as a reminder of the importance of such measures.

“When you look at the amount of shaking that took place in Pasadena, it wasn’t that large,” Kohler said in reference to the recent earthquake. “And so we should really be prepared for a larger amplitude, larger amount of shaking, that is likely to take place if a larger magnitude earthquake takes place on some of the faults that are close to Los Angeles,” she said.