Monday, February 21, 2011

What is "The Big One," anyway?

There’s no doubt that you have probably heard that us BC-ers and everyone else along the Pacific coast are due to have a huge, catastrophic earthquake at any time. The wonderful tag line, "at any time," is probably used to encourage us to be well-stocked on water bottles and a feast of cat food in our basement somewhere. Naturally, it more likely strikes extreme fear into the bottom of our hearts knowing that there is always an ominous looming of being crushed under a blue whale as it gets washed ashore from the 900 billion foot tsunami we expect to sweep over whatever city we'll regret being in at the time. Before you start installing your apartment with the latest in sea-drainage technology and a shock system, let's get the facts straight.

View Cascadia Subduction Zone in a larger map

The menacing earthquake in question is technically called a megathrust earthquake, and this indicates a sudden slip along the boundary between a subducting and an overriding plate (i.e. a megathrust fault). Basically, all the devastatingly gargantuan earthquakes you hear about in the news for weeks are megathrust earthquakes. We are currently perched along the Cascadian fault line, and although we don't have any written history on the last big shake-up, we have some clues to make some rather strong assumptions on.
  1. Those impressively huge trees along the coast have strange changes in tree ring growth, suggesting a sudden, pandemic regression of roots.
  2. Geologists have discovered sand bars gone awry sitting on buried tidal marsh and forest soils of about the same depth from BC all the way down to California.
  3. There's evidence of strong seismic activity from the detection of landslide layers (aka. silt turbidite) a distance off the west coast.
  4. It's clear a tsunami took the unaccommodating westcoast by storm with confirmation of preserved sea organisms that were discovered in the bottom of lakes, often separated by land elevations of 5 meters high.
Centuries ago, there was a tsunami in Japan without the presence of a local earthquake, but before you label this as magic this isn't some ghost tsunami. This waterloo was caused by the most recent huge Cascadian earthquake on the calamitous evening of January 26, 1700. Just in case you still aren't buying it, there are even legends among first nations people describing a "severe ground shaking on a winter night accompanied by huge waves that destroyed a coastal village."

Juan de' rumble?
It has been estimated that the northwest can expect a one in three chance for a magnitude 9.0 earthquake within the next 50 years. In all seriousness, the only thing we can really do is be prepared with 3 days worth of beverages and toilet paper, a little awareness for safety, and a mix tape of Chumbawumba's "Tubthumping" to shake up the mood. Although that may be a little inappropriate. I get knocked down...



  1. I love Chumbawumba, great song :P

  2. the "big one" is about as realistic as tupac's resurrection
    it's not going to happen!