Janis Hernandez, a senior engineering geologist who heads California Geological Survey’s Los Angeles office, long wanted to visit the U.S. territory of Puerto Rico. She can cross that off her bucket list, though she might have chosen different circumstances for her visit.

“Well, I ended up seeing a lot more of the island than most tourists,” she said after spending 17 days on the island recording the damage done by a recent series of earthquakes.

Joining the mainland response team

An earthquake swarm — including 11 quakes magnitude 5 or larger — began in the southwestern part of Puerto Rico in late December 2019.

The largest and most damaging quake in the sequence was a magnitude 6.4 on January 7, 2020. It was directly responsible for one fatality and did extensive property damage. Hernandez was invited to join a California Office of Emergency Services (CalOES) team, part of the second wave of mainland responders. The team arrived in the capital, San Juan, on February 3.

“The CalOES staff had a lot of different roles and they were looking for an earthquake subject-matter expert,” Hernandez said. “The response was an all-hands-on-deck situation.”

The OES group focused on documenting damage to residential structures – important in evaluating safety and the need for relief funding. Hernandez’s role was to provide geologic insight about what had occurred and what the future might bring.

Looking beyond the shaking for secondary hazards and their effects

Shaking causes most of the damage in large earthquakes; but Hernandez focused on impacts of secondary hazards: surface fault rupture (cracks in the ground where a fault had breached the surface), landslides, and liquefaction (the ground temporarily turning the consistency of Jell-O).

“There wasn’t surface fault rupture to speak of, but there certainly were examples of liquefaction and earthquake-triggered landslides,” she said.

“Then, as the aftershocks continued, there were zones of subsidence (the ground sinking) in the main damaged areas…some of the beaches and coastal properties had flooded and were permanently under a foot of water.”

Puerto Rico is used to dealing with the temporary storm surge associated with hurricanes. Many homes close to the ocean are built on piers.

“But with subsidence, those surges will be even higher than they’re used to, which brings a serious problem for some people in the future,” Hernandez said.

Hernandez was especially interested in how schools fared

“Many did not perform well at all,” she said. “What often happens is that developers turn a particular design into a cookie-cutter and repeat it over and over.”

“I saw several schools where the top two stories had pancaked into the ground floor, which is alarming since Puerto Rico is in an active seismic area.”

Hernandez combined her personal observations with ground-motion data and observations provided by USGS. She teamed up with CGS colleague Kate Thomas to produce a shaded “heat” map showing where earthquake-induced landslides had occurred and where more might be expected as aftershocks continue in the coming months.

Although she didn’t get to do much sightseeing, Hernandez did have the opportunity to interact with many locals as she found her way around impacted parts of the island.

An enlightening experience

“The residents in communities, and people operating businesses were very nice, willing to describe what had happened, and were very helpful,” she said.

“It seemed like they were all hanging in there OK. It was enlightening to find out what they were going through, the challenges they’d faced, and what help they needed.”