Mapping Tsunami Hazards in California: When Experience Meets Expertise

Nick Graehl, engineering geologist in California Geological Survey’s Tsunami Program, often reflects on his first post-tsunami reconnaissance trip as a reminder of the importance of preparing Californians for a tsunami.

“It’s something not everyone gets to experience but then once you have, you never forget.”

From Studying to Experiencing Tsunami Effects

A post-tsunami reconnaissance trip, or post-tsunami survey, is a scientific evaluation of an area recently impacted by tsunami.

For Graehl, this happened in 2010, in Chile. A magnitude 8.8 earthquake triggered a devastating tsunami. He was not well prepared for the event.

The 2010 Chile tsunami resulted from a magnitude 8.8 quake that struck on Saturday, February 27 at 3:34 a.m. local time.

First, he had to leave his wife alone with their 10-month old baby, “that was hard enough right there.”

Then there was the firsthand experience, witnessing tsunami destruction created just weeks prior, and meeting the people who survived it. A stark contrast to reviewing centuries old tsunami sand deposits, which Graehl had been studying prior to the Chile earthquake.

Graehl recounts, “Studying the science behind prehistoric earthquakes and tsunamis is one thing, but observing the tsunami aftermath weeks after an event is something that I will never forget.”

“I’m a paleotsunami scientist by training but what happened to the local residents was…I can’t even put it into words.”

Nick Graehl, California Geological Survey Tsunami Program Engineering Geologist

Witnessing the Damage Firsthand

The earthquake struck on the final weekend of summer, just off the coast. Beaches were packed with visitors from all over the area, many still awake watching fireworks or partying at 3:30 a.m. when the fault rupture began, about three kilometers offshore. About 370,000 homes were destroyed, 525 people died, 25 people went missing. Losses were estimated at up to $30 billion.

Graehl (right) stands in front of tsunami debris with then-geology professor Lori Dengler.

“What was left standing in the inundation zone was either badly damaged or completely erased as buildings were ripped clean off their foundation from the tsunami.

“In one particularly hard-hit town, I remember seeing the remains of toddler toys strewn about. Some were the same toys as my son back home, and that’s when it really connected on a personal level for me.”

Remains of kids toys at a shrine. Reminder of Graehl’s family and 10-month old son at home.

When it comes to applying lessons learned, he takes the job seriously.

“I’ll carry that experience with me the rest of my life. It does influence how I conduct myself at work.”

Learning from Chile for California

Graehl reflects on the Chile trip regularly, as a reminder of why communicating hazards is so important. For Californians, that means knowing what your risk is, by knowing where the risks are.

There are two worst-case tsunami sources in California: North of Cape Mendocino and South of Cape Mendocino.

Graehl explains, “North of Cape Mendocino, the highest hazard comes from a local tsunami source- the Cascadia subduction zone; South of Cape Mendocino, the worst-case is a distant source tsunami generated from the Alaskan Aleutian Islands. “

Knowing how to react to each one in a real event will help save your life.

Then, Japan’s Tsunami Hits California

The year after his Chile trip, Graehl practiced his own advice when a magnitude 9.1 earthquake occurred in Japan and triggered a tsunami. Though he was home in California, now with his toddler and new two-month old baby, they lived near a tsunami hazard zone.

“I remember being very concerned at the time because my wife would need to commute to work through a tsunami hazard zone. That was a big deal for me.”

He looked up routes they travel from home to work, cross referencing hazard maps and evacuation zones. “It was an opportunity for us to discuss our own family emergency plans,” he said.

Channeling His Passion at California Geological Survey

Ten years later, Graehl contributes his expertise and first-hand experiences to CGS’ tsunami program. The team recently developed a 10-year commemorative reflection of Japan’s 2011 quake and tsunami and a California Tsunami Preparedness Guide to help explain their new Tsunami Hazard Area Maps.

Graehl also helped coordinate the release of updated tsunami hazard maps for 13 of the state’s 20 coastal counties: Alameda, Contra Costa, Del Norte, Humboldt, Los Angeles, Mendocino, Monterey, Orange, San Francisco, San Luis Obispo, San Mateo, Santa Barbara, and Santa Clara.

California’s state tsunami website is

As lead tsunami mapper for Los Angeles, Monterey, Orange and Santa Barbara counties, he worked closely with county and city emergency officials to finalize these maps and assist communities with updating their own disaster communication materials.

Next, he’s focusing his sights on other parts of California as he continues updating tsunami hazard maps for Santa Cruz and San Diego counties.

“Seeing the devastation first-hand and its impact on families…that just brings it home. It is so important for people to plan, prepare, and be aware.”

Plan, Prepare, Be Aware

Graehl admits preparing for natural hazards can be daunting – especially in California where tsunami hazards fall into the shadow of well-known earthquake hazards. But he encourages Californians to start small…then work up to more involved tsunami preparedness activities.

For a first step, visit the CGS State tsunami website at

Graehl with his son in California.

Leave a Reply