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Could a dangerous Tsunami hit Southern California?

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Adam Wright
by
(Saturday) 9.7.13

I caught an article from the LA Times the other morning talking about a study put together by the USGS (United States Geological Survey) that shows how much potential damage Socal might take from a Tsunami triggered by a large, (but not totally implausible), sized earthquake occurring in Alaska. As most of you already know, I nerd out on waves, weather, (and get even worse if it has maps in it)…so I powered through the article and went on to go and read through the study directly from the USGS website. (Here is the link If you want to check out the study yourself)

The USGS based their data on a theoretic 9.2 magnitude earthquake centered around the Alaskan Peninsula, potentially out near some of the shallower areas nearby the Aleutian Islands. This earthquake would have to create some serious water displacement by moving a massive amount of sea-floor up (or down) and/or cause a number of undersea mountains or sea-shelf to collapse.

Initially there weren’t a lot of surprises in the study. California’s unique geography actually protects much of our coast from tsunami events. Most of Northern and Central California as well as a lot of Southern California have long stretches of coastal hills and high cliffs that come almost directly to the water’s edge, those types of land features do a good job preventing the surging nature of the tsunami from pushing inland into populated areas. Of course the report does point out that there are enough portions of the coast that don’t have the coastal hills/cliffs to protect them…and it is these flat, low lying, coastal areas that always get hit the hardest by Tsunamis. Bays, harbors, inlets, river-mouths and other land/ocean features that focus wave energy back in on itself are particularly dangerous.

What I did find particularly interesting, and much more relevant, is how the USGS took into account the various infrastructure that we have built up along the coast here in Southern California. They point out that between the various areas of high cliffs and coastal hills that the loss of life from the tsunami wave event, with enough warning, would be on the low side. That is pretty good news, BUT then they go into what could happen to the various power plants (non-nuclear), the oil platforms, the big harbor based transportation/distribution centers…all of which sit in the low-lying areas.

They point out that a relatively good-sized tsunami would cause what is called ‘sediment scouring’, which is when the tsunami redistributes potentially polluted/contaminated sediment in areas like the Port of LA/Long Beach, from the flood control system, or the gnarly areas around our different sewage treatment plants. Hell they even looked into what would happen to the near-coastal areas if the tsunami wiped out a built up residential region, like Newport Beach/Newport Harbor, and how many issues would arise from common household chemicals, things like cleaning agents, oils, lead-based paints, old asbestos based construction leftover in older seaside homes.

They propose that while we wouldn’t necessarily get hit by the physical wall of water, the destruction of this infrastructure could still render much of our near-ocean areas unusable for a fairly long time. Really what it boils down to, is that even without the loss of life our current ocean culture would have to face some serious changes for a while and that a significant Tsunami impact in Southern California would be an environmental disaster and massive financial burden.

There is some sort of good news in the report. Like I mentioned before, if we have enough lead time to evacuate, which we would if the Tsunami was a transoceanic event (meaning it had to travel across a significant amount of ocean to reach us), the USGS indicates that “If the scenario’s expected evacuation of populations from the inundation (impacted) zone were to be successful, there could plausibly be few or no drownings or other tsunami-related casualties, crushing injuries, puncture wounds, or infections.” California Geological Survey Special Report 229 I don’t know about you but not being drowned, crushed, or punctured sounds pretty good to me.

The USGS does look a little further down the road at both potential human health implications and the post-tsunami cleanup and recovery…and they feel that is possible to recover/rehabilitate the damaged areas, and prevent any secondary loss of life from contamination if we take reasonable measures in the cleanup and containment process. HOWEVER that statement needs to be hedged a little bit…the USGS may be looking at a post-tsunami area with glasses that are a little too rosy…humans are pretty good at not following rules, or taking reasonable measures, not to mention that we are really good at generally being pains in the butt…so anyone thinking everything is going to run along nice and smooth after a major disaster, needs to spend some time looking at how we reacted to things like Superstorm Sandy or Hurricane Katrina, in order to have a more realistic view of how the recovery could potentially go.

At any rate, I get questions about Tsunami’s hitting Southern California all the time, and thought that I would share the findings that the USGS came up with, since they specifically focused the report on our area.

If you are looking for more personal safety information here is USGS video from 2010 talking about Tsunami safety and what to do if we ever hear the warning sirens go off. It isn’t the most exciting video (it was made by the government)…but like most government videos there are some unintentional comedic moments…and surprisingly they even included a few surfing clips in there as well.

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  • jacks

    if only newport would get swamped out on july 4th