Why Magnitude 5.1 Quake Did So Little Damage to Bay Area

Read Time:5 Minute, 32 Second

(TNS) – A rumbling, 5.1 magnitude earthquake rattled a large swath of the Bay Area on Tuesday morning, with residents reporting feeling the temblor from San Jose to the East Bay.

The quake struck the Calaveras fault zone at 11:42 a.m., with an epicenter on Mount Hamilton nearly 9 miles east of the Seven Trees neighborhood in San Jose, according to the U.S. Geological Survey. Seismologists recorded a 2.9 magnitude aftershock roughly five minuteslater. Shortly after 3 p.m., a quake measured as magnitude 3.5 hit in the same area.

The state’s earthquake early warning system notified nearly 100,000 people that a quake was going to strike — and people as far away as San Francisco had as many as 18 seconds to brace themselves before it actually hit, according to the state Office of Emergency Services.

Although many people in the area described an intense swaying that lasted around 30 seconds, the quake evidently did not leave a trail of devastation.No gas leaks, damages or injuries were reported in Santa Clara County, according to the county Office of Emergency Management.

In San Jose, buildings swayed and workers spilled out of them. In San Francisco, residents and workers felt the ground rock.

Changes in building codes over time helped insulate the city from major destruction, San Jose Department of Emergency Management Director Ray Riordan told The Chronicle. He cited the abundance of single-story, wood-frame homes in San Jose that are bolted to the foundation, keeping them safe when the earth quivers.

“We have older buildings and soft-story buildings, but we’re working to address that,” Riordan said, adding that Tuesday’s earthquake was “far enough away” and “deep enough” to have little impact on a large, populous city.

“Ground shaking appears to have been slightly less than our models expected for this magnitude earthquake,” USGS seismologist Annemarie Baltay said in a video statement
on social media.

But if the quake did not meet predictions, it still caused a powerful spasm that ricocheted throughout the region.

The Santa Clara Valley Transportation Authority halted service for 15 minutes following the temblor to survey possible damage to its trains, the agency said. Service resumed soon after engineers determined that none of the agency’s trains or stations had been affected. Caltrain briefly

slowed commuter service on the Peninsula.

South Bay residents described an undulating sensation.

“It felt like our house was a boat,” said Colin Heyne,a spokesperson for San Jose’s Department of Transportation, who was home in the Olinder neighborhood with his sick 5-year-old son.Heyne ran in the doorway and struggled to get his child to stay put until the wobbling subsided.

Moments later, he received a flurry of texts from people working in the 18-story City Hall building — a modern tower designed to swing in an earthquake, and give anyone inside a harrowing ride.

While the earthquake had not damaged any San Jose city facilities, Mayor Sam Liccardo encouraged residents to take precautions for the future.

“A far more damaging earthquake inevitably awaits, so we should look upon these mild tremors as blessings, to remind us all to create a family emergency plan, and prepare a disaster kit,” Liccardo said in a statement.

He urged residents to create emergency plans using the website www.ready.gov.

Preschool teacher Lidia Atkins was at the playground with her pint-sized charges Tuesday when the shakingbegan.

“I blew my whistle and the kids went to their places,” Atkins said.

The owner of Lidia’s Preschool and Daycare Center in south San Jose said she followed her school’s earthquake protocol, which they practice in monthly drills.

On Tuesday, she blew her whistle and the confused kids went to shelter under a bench on the playground.

“The 4-year-olds follow directions,” she said. “The 2-year-olds wander around saying, ‘What’s going on?'”

The preschool staff checked their building and classrooms for damage. Finding none, they returned to their lessons.

Tuesday’s quake was the biggest since the 6.0 magnitude temblor that struck Napa in 2014. While earthquakes are common in the Bay Area and adjacent counties, those of magnitude 5 or greater are relatively rare.

Only eight earthquakes that large have hit the area since the devastating 6.9 magnitude Loma Prieta earthquake struck near Santa Cruz in 1989, according to the U.S. Geological Survey’s tracker.

Spokespersons from National Weather Service in the Bay Area said employees felt the earthquake at the office in Monterey. According to USGS data, the quake’s epicenter was just south of Mount Hamilton in the hills east of San Jose.

Eve Laraway, who owns Eve’s Answering Service and was responding to calls for the Grandview Restaurant, an upscale Italian establishment located near the earthquake’s epicenter, said she was worried the restaurant may have had damage from the earthquake. Spokespersons from the restaurant were not immediately available to respond.

“There’s all kinds of glassware hanging there,” said Laraway, who told The Chronicle she felt the earthquake in Menlo Park sitting at the same desk she was sitting in during the Loma Prieta earthquake nearly 33 years ago to the day.

Jenn Zipp, who works for the San Francisco gift shop Rare Device, said nothing in the store was affected. By the time a co-worker in the Inner Sunset managed to send a message about the quake, Zipp said employees at the gift shop felt the earthquake.

“It was as if it was moving through San Francisco at the same rate as we were getting messages about it,” she said.

Craig Clements said he felt jostled on the eighth floor of Duncan Hall at San Jose State University, about 11 miles from the epicenter of the quake. The shaking seemed dramatic, even by the standards of a California native members the 1989 Loma Prieta quake, which caused 63 deaths and 3,757 injuries.

“All the cubicles were shaking,” said Marcus Ismael, a spokesperson for the university who was on the top floor of the five-story campus administration building when the convulsion began. He characterized the 30 seconds as “anxiety inducing,” particularly for people just returning to the office after working from home.

Chronicle staff writer Jack Lee contributed to this report.