The BIGGER BIG ONE

Steve's picture

If you live in California and conversation drifts to earthquakes, the “BIG ONE” always surfaces.

 ‘Hey Steve, when’s the next BIG ONE coming?’

For out-of-towners, a BIG ONE refers to a ~M8 earthquake on the San Andreas Fault. The last BIG ONE was the 1906 San Francisco earthquake. Everyone knows that. The BIG ONE before that was the 1857 Ft. Tejon earthquake in the southern part of the State. Virtually nobody knows that. No surprise, in 1857 Los Angeles was a dusty backwater, home to about 4,000 townsfolk.

 As much as it might crimp a Californian’s bragging rights, a BIGGER, BIG ONE is in the neighborhood -- A Cascadia Earthquake. The Cascadia Fault starts at Cape Mendocino, just where the San Andreas Fault ends, and it runs northward offshore of Oregon, Washington and British Columbia to the southern tip of Queen Charlotte Island. Cascadia is a subduction zone fault versus a strike slip kind like the San Andreas. The primary difference is that subduction zone faults dip gently into the Earth while strike slip faults cut into it vertically. Thus, the seismically potent “width” of the former can be 10 or 15 times the latter. Bigger fault area means larger potential earthquakes all else fixed. A Cascadia quake might be M9 or M9.3. The BIG ONE on the SAF is a mere pup, in comparison.

The last BIGGER BIG ONE in Cascadia happened January 26, 1700. How do we know this? Turns out that the tsunami wave traveled all the way to Japan and damaged some goods stored at various harbor locations. Insurance agents (yes, those guys have been around forever) took careful note of the losses and their records still exist. It’s been 300 years since then, the fault has reloaded and might discharge again at any time.

This movie visualizes the tsunami that the BIGGER BIG ONE might spawn. True, the movie waves have been exaggerated several 100 times in size to make them visible. My guess though, if you were standing on an Oregon beach and saw a 30 foot high wave coming at you, distinction between exaggeration and reality would hardly matter.

OK, sure, maybe BIGGER BIG ONES exist. For seismo-centric Californians however, big ones (lower case) in some another state, just don’t count.

Steven N. Ward     Santa Cruz

Comments

jamekurt's picture

help: i like the movie because it is picturizing the natural disasters like earthquack and  floods etc. this movie also visualizes the tsunami that the BIGGER BIG ONE might spawn which is true.

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