J. Peters asked, in response to my last post: "How real is a big tsunami threat for California or Hawaii?"

Great question. Thanks for asking. As this is of regional importance, I’ll reply here.

In terms of a 30-year mortgage, the short answer is:”? It’s "uncertain" (in the statistical sense) — but that doesn’t make it any less "real" (in the, well, real estate sense).

Experts at the US Geological Survey (USGS) and National Oceanic and Atmospheric Administration (NOAA) have been studying this question in earnest for the last few years (in part to update FEMA flood maps along the coast). While we await their answer, you can be the judge. Here are the clues:

Tsunamis are caused by forces that suddenly raise or lower sea level. Big tsunamis in the Pacific Ocean are typically due to huge earthquakes on any of the dozens of major undersea faults around the Pacific Rim. Large submarine landslides (often triggered by large earthquakes) can cause big tsunamis locally. And "bolides" crashing into the sea (meteors, asteroids, and comets) can cause big tsunamis regionally (remember "Deep Impact"?).

(Remind me to tell you about "Apophis," a chunk of space rock as tall as the Empire State Building traveling 28,000 mph. It’s due to skim past the earth just 21,000 miles above the ground — only a bit farther away than that GPS satellite your dashboard navigator talks to — on Friday the 13th of April, 2029, at 4:36 am Greenwich Mean Time. It’ll be the first asteroid in human history to be clearly visible to the naked eye, and capable of causing an 800-foot tsunami if it splashed down. The experts are almost certain that it won’t. Not in 2029 anyhow. They’re not so sure about its next pass in 2036. But I digress.)

For this answer, we’ll consider a "big tsunami" to be one that crosses an ocean basin (NOAA calls these "ocean-wide" events) that is generated by a major earthquake.

The threat of a destructive, ocean-wide tsunami is real enough that, half a century ago, the US established two Tsunami Warning Centers, one to serve Hawaii and the other, the Pacific Coast. They operate 24/7, ready to issue watches and warnings within minutes of undersea earthquakes in the Pacific Basin that exceed magnitude 7. The warnings advise coastal dwellers to take response actions that are appropriate for the particular tsunami event, such as evacuating low-lying coastal areas, and moving boats and ships out of harbors to deep water.

Hawaii suffered the biggest and most ocean-wide tsunamis to strike the US in the 20th Century, including the following "Big Ones" (source: NOAA):

April 1946. Cause: Magnitude 8.1 earthquake in the Aleutian Islands. Tsunami exceeded 40 feet in Hawaii (96 deaths in Hilo), and up to 12 feet along the central California coast (1 death). No warning systems existed at that time.

May 1960. Cause: Magnitude 9.5 earthquake along the Chile coast. Tsunami exceeded 30 feet in Hawaii (61 deaths in Hilo; Hawaii warning system existed, but onlookers ignored the warnings), and 7 feet along the central California coast (3 deaths; no West Coast warning system existed yet).

March 1964. Cause: Magnitude 9.2 earthquake in the Gulf of Alaska. Tsunami exceeded 16 feet in Hawaii (0 deaths; smaller waves than in 1960 and, apparently, the warnings worked), and 20 feet along the northern California coast (13 deaths; West Coast warning system wasn’t established until three years later).

According to NOAA, a destructive ocean-wide tsunami occurs about once every 15 years (long-term average). Hawaii and the West Coast have not experienced a "Big One" since 1964.

As your stock analyst says, "past performance is no guarantee of future results" — but I wouldn’t bet the farm on four more decades without another big tsunami here!

FYI: NOAA has a great list of tsunami FAQs that you’ll find interesting. Check it out if you have time.