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A Tsunami on My Block?


(Editor’s Note: The following is Part 1 in a Series Looking at Issues Raised by the Japan Earthquake and Tsunami. It is a revised version of a letter to the editor, which originally appeared at Santa Monica LookOut

I live steps from the Pacific Ocean in the Ocean Park neighborhood of Santa Monica, California. When the recent horrific 9.0 earthquake hit Japan, I knew a local tsunami watch would be coming and I might have to evacuate. This would be our second watch in a year – in February 2010 there was an 8.8 earthquake in Chile that raised similar concerns up and down the Pacific Coast. This time I started getting calls from friends soon after the quake hit in Japan, worried I hadn’t heard the news. Knowing the tsunami wasn’t scheduled to arrive locally until approximately 8:39 a.m. the next day, and that its effect might not be gauged until it had at least reached Hawai’i, I went to sleep as usual and planned to awake around 7 a.m.

Wasn’t that a little late to begin planning for a possible cataclysm?

Faults of Southern CaliforniaLong before the December 2006 Aceh province (Indonesia) tsunami, I’ve been acutely aware of the possibility of either a cross-Pacific ‘distance source’ tsunami reaching Santa Monica like from Japan or Chile, or a locally-generated one caused by an underwater off-shore landslide triggered by an earthquake, with both the Palos Verdes and Santa Cruz – Santa Catalina Ridge Faults just off the coast and the Newport-Inglewood Fault just a few miles inland. In addition, the block upon which I live is is at high risk from liquefaction from an earthquake. So I’ve been thinking about evacuation for a long time.

Most of Santa Monica is on one of two high plateaus above sea level. But my neighborhood is at the city’s lowest point, and my house itself is maybe 35 feet above sea level. With some advance warning, I could easily flee on foot, rollerblades or bike a mile or two to safety. But if I didn’t have much notice, things could be different. Under a worst case scenario, my block is in the tsunami ‘inundation zone’ and could go under water, according to Los Angeles Tsunami Hazard: Maximum Runup, a study by the Governor’s Office of Emergency Services.

Fortunately, just four blocks inland is a very high hill that is the designated place to go in Ocean Park by the Santa Monica’s Emergency Services. I’ve always hoped that as long as I had at least a few minutes warning, I could jump up on my bike or even run up the hill and save my life, even if it meant leaving my belongings behind.

What does a person bring if they only have a few moments to decide and can only take a few things?

If I only had a minute or two to run, I would take my glasses and contact lenses, credit card, ATM and cash; and would reach for a good pair of shoes, if I wasn’t already wearing them. Then I’d head up to Fourth Street fast. But if I was reacting to a cross-Pacific tsunami, presumably coastal LA County would have hours of advance warning. With such notice I could pack and take my car somewhere to higher ground in Santa Monica or further inland. At a minimum I could pack boxes of old pictures and memories, my computer hard drives and my shirts, pants and sport coats.

But what if had only 30 minutes to flee a local tsunami? If my house was going to be washed away, should I take ten minutes to grab and preserve as many of my core belongings and drive up the hill to save my ten year old (but still in excellent condition and fuel efficient) Prius? Or would that endanger my life? What if I had 20 minutes? 15? Might others in the neighborhood try to do the same thing, making it impossible to drive anywhere with people acting out of panic? One hopes public safety personnel would be directing traffic to specific destinations in such an emergency, but who knows if they could even know and deploy in time?

Clearly it would be tragic to lose one’s life by being materialistic and trying to hold on to a few items instead of escaping promptly to safety. On the other hand, if you are about to lose your home and worldly possessions forever and you had the chance to save a few key items and your car and be safe at the same time, and you didn’t do it, would you regret it? …hmmmm. Maybe I should start now by paying someone to scan the hundreds of old pictures I have in shoe boxes and take that worry off my head, figuring its money well spent.

As standard practice, I already keep a pillow, sleeping bag, drinking water and some dried vegan proteins and other snacks in my car and usually keep my gas tank at least half filled in case I am stranded anywhere because of a natural disaster. These are the things of life in the world of climate change, earthquakes and tsunamis.

Would the day begin with a tsunami?

I awoke at 5 a.m. to a warning call from another friend. I am not an early morning person. Since the waves weren’t expected to arrive for another three and a half hours, while I appreciated my friend’s intent, I was miserable and desperately tried to get back to sleep until my alarm would go off. If the day was going to bring a massive local natural disaster and I was going to become homeless, I wanted to be well rested.

Before putting my head back under my pillow, I turned on the news to hear that the tsunami’s effects upon Hawai’i had not been catastrophic, and that the National Oceanic and Atmospheric Administration had issued only a tsunami advisory for Southern California, not the more severe tsunami warning they did for further north, from Point Conception in Santa Barbara County to the California-Oregon border. According to a press release issued by the city of Santa Monica: “A Tsunami Advisory indicates that a tsunami capable of producing strong currents or waves dangerous to persons in or very near the water is expected. Significant, widespread inundation is not expected for areas under an advisory. Currents may be hazardous to swimmers, boats, and coastal structures and may continue for several hours after the initial wave arrival.”

Relieved and thrilled that we were not in imminent danger, I went back to sleep for a few minutes but was soon re-awoken by more calls from well-wishers, meaning sleepy time was over. Giving into the day, my head soon filled with the sound of helicopters. Police choppers were trolling the shoreline to get people out of the water and away from the water’s edge, while news helicopters hovered above waiting for their story. It sounded like a war zone. But when I turned on the TV and saw a reporter literally broadcasting from my corner about how it looked like another perfect day in LA, with sunshine and calm water in the bay, I was giddy and put on my shorts and sandals and cranked up a great live version of Randy Newman’s I Love LA (from Saturday Night Live: 25 Years of Musical Performances, Vol. 1.) With my fanny pack full of a camera as well as my credit card, cash and glasses just in case, I rolled down to the corner on my beach cruiser. The atmosphere was celebratory, accented by a curiosity of what would happen at 8:39am. It felt like my neighborhood was out to watch a marathon or parade, both of which have passed by my corner from time to time (even the 1984 Olympic marathon, both mens and womens.)

Happy DogI ran into a guy who works at Perry’s, the local beach bike rental shop. He pointed to this big dog in a nearby pickup and said its calm mood was why he knew there wouldn’t be a problem, because animals can sense danger first. Comforted, I still didn’t head to the water’s edge, because if there was to be any danger, it would be from a quick wave surge that grabbed somebody and washed them out to sea.

That’s what happened to several people who were too close to the water during the great El Niño storms of 1982-83, that wracked Southern California and destroyed 1/3 of the length of Santa Monica Pier. Back then the waves reached all the way into the parking lots north and south of the Pier, and today the city had closed the beach lots and the Pier itself just to play it safe.

Santa Monica Pier HistoryFortunately there was little impact this time around and the pier and beach lots were re-opened by early afternoon. “A mitigating factor was that this occurred at low tide, meaning there was no rise in sea level”, according to Paul Weinberg, the city of Santa Monica’s Emergency Services Coordinator. “Had we had been at high tide (approximately four and a half feet) and then added an additional two to three feet of water, the impact could have been more significant.”Where the damage happened and why

Most of the tsunami-related damage in California was in Del Norte, Humboldt, San Mateo and Santa Cruz counties, all north of Point Conception where there was a tsunami warning rather than an advisory. Point Conception is north of Santa Barbara and is the dividing point between the mostly north-south trending portion of California to the north and the east-west trending part of the coast southward to the Mexican border.

Pt. ConceptionWhen I tried to understand why a warning was issued to the north and an advisory to the south, I heard something repeated that I’d heard over the years, that the south and south western facing coastline in Southern California would not take a direct hit compared to the west-facing coastline further north. This line of reasoning never made any sense to me, especially if the tsunami was a few hundred miles wide and would hit both north and south of Point Conception. In other words, what difference would the angle of the coastline make if it was hit by a 20-foot high wave?

To get a clear answer, I called the National Oceanic and Atmosphere Administration (NOAA) National Weather Service West Coast and Alaska Tsunami Warning Center in Palmer, Alaska and spoke with a very well informed staff member there named Cindi Preller, who wears many hats – Tsunami Program Manager for the Alaska Region, Director of Education and Outreach, Warning Coordination Scientist and a Watchstander and geologist. She confirmed my intuition that the angle of the coast was not the primary variable, but rather it was a combination of large-scale conditions that NOAA can predict with some modeling and accuracy, and local conditions which often are only modeled locally, if at all.

On the macro-level Ms. Preller explained that near the California-Oregon border along the ocean floor, there is the Mendocino mountain ridge, which reaches 3,000 miles to the Emperor sea mounts north of Hawai’i. An earthquake of a 9 magnitude, she added, normally causes a seismic disruption at least 800 kilometers wide. In this case, tsunami seismic force vector originally traveled from Japan in the direction of Hawai’i. But the presence of the Mendocino ridge redirected part of it towards Oregon and central and northern California, with the rest continuing onward to the Southern Hemisphere. It was for that reason that a warning was posted for north of Point Conception and an advisory to the south.

What made the tsunami’s effects different at different points along the central and northern California coast? Ms. Preller explained that the near shore local topography and geology would determine in a very non-linear way how severe the impact would be. Each bay, each beach would have its own full basin set of conditions that could either accelerate or slow down the length and amplitude of the waves. Such analysis is beyond the ability of West Coast and Alaska Tsunami Information Center to calculate and this is where we are all dependent upon local modeling and planning.

Distance source and local source tsunamis – what’s the difference?

While the ‘distance source’ tsunamis that came to Santa Monica from Japan and Chile in the last year did little to ‘make waves’ locally, a ‘local source’ tsunami resulting from ocean-based landslides triggered from a local earthquake could be far more powerful than something traveling all the way across the Pacific Ocean, and would likely provide little or no warning.

According to Ms. Preller, all earthquakes can cause landslides. Locally we have two off shore faults and the Newport-Inglewood fault all close by to Santa Monica. The off-shore faults are called thrust faults and occur when a part of one plate rides up over another at a shallow angle. The are other faults, both on and off shore called strike/slip faults, which is where one plate rubs sideways against another going in the other direction. These faults release less energy than subduction faults like we just saw off of Japan, where one plate goes underneath another severely recycling rock back to the earth’s mantle from which it came. Therefore according to Ms. Preller, the off shore thrust faults nearest to Santa Monica have been modeled to produce earthquakes only up into the 7.0 range – nearly 1000 times less energy than the 9.0 in Japan but still certainly very powerful. With such a tsunami, it might only be 20-30 minutes before it started hitting shore, or even less depending if the earthquake triggered a landslide very near shore. Who knows how long it would take to even realize this is happening? Even a few minutes could mean the difference between life and death.

To understand what kind of ocean-based landslides could be caused by a 7.0 quake, I called and emailed the US Geological Service (USGS) to ask about offshore soil stability. I heard back of a study of Santa Barbara Channel, but nothing yet specifically for the area off of LA County. I’m sure they are getting a lot of questions like that this these days. That’s a reminder of how ‘pennywise and pound foolish’ are the counter-productive attempts of Congressional House Republicans to slash the budgets of the USGS, NOAA and NWS (National Weather Service), including even the Pacific Tsunami Warning Center that has been informing us of the potential danger from the events in Japan!

But I did find reference to a scenario proposed by Jacques Locat, Chair of the Department of Geology and Geological Engineering, Laval University, Quebec. He calculated what could happen if a 300-foot-thick rockfall were to slide down the Palos Verdes peninsula’s escarpment into the sea. Plunging to a depth of more than 2,000 feet, the rockfall would generate a huge, surging wall of water — a local tsunami that would batter the coast with a wave at least 100 feet high, he said, and give people on the shore at nearby Long Beach just 24 minutes to climb to safety.

What’s needed the article concluded, is that at least for California if not for all the world’s coastal nations, is to map the seabed wherever offshore slopes dip steeply enough to pose the threat of submarine landslides and the deadly tsunamis they are capable of generating.

Next: Part II: Tsunamis, Nukes and Climate Change

04/08/2011 – 12:00


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