[PLUG-TALK] The Big One

[Keith Lofstrom]

The Cascadian subduction zone is building strain at about 4 centimeters
per year.  The last time it kicked loose, in 1700, the tsunami left sand
at the top of coastal cliffs, wiping out the coastal native tribes, and
killed people in Japan.

There is now more than 12 meters of strain across an area about 1000km
north-south and 200km east-west, about 40 km below us, with the
fault slanting upwards to surface out in the Pacific.  Eventually,
that entire fault area fractures, and the Juan de Fuca plate slides
a few meters east, and we slide a few meters west.  That doesn't
sound like a lot, but the movement is fast, and the velocities and 
accelerations are high.   The whole thing shakes like jello, for
minutes, with hundreds of aftershocks repeating for days.

Geologists estimate that there is about a 10% chance of the zone
zone fracturing in the next 30 years - if it does, it will probably
be above Richter 9, and may be the largest earthquake in recorded
history.  While the Richter scale isn't all that meaningful above
Richter 7, it is logarithmic, and every extra Richter number corresponds
to an increase in ground acceleration of 10x, which corresponds to
an energy increase of 100x (amplitude squared).   As I understand it.

As near as I can tell (the literature is vague), building code for
new construction is designed for minimal loss of life in a Richter 7. 
California is 7.5 .  We get fewer earthquakes in Oregon, the "frequent"
ones are mere Richter 5's to 7's.  But a megathrust Cascadia quake would
be far larger than anything California has experienced historically. 

It would probably exceed the 1964 Alaska quake, which killed 100 people
in Alaska (out of 250,000).   Granted that most of them were killed
by tsunamis on the coast, only about 10 from structural failure.  
While we may lose tens of thousands of people on the coast,  we will
probably lose more thousands inland, proportional to a much higher
population than Alaska.

The reason I bring this up is that we are planning a move to
another house, and while it is built better than the one we are
in now, it would be good if it could survive the Big One.  So,
besides fixing up the electrical and insulation, and strapping
the water heater better, we are also considering adding more sill
bolts, structural plywood, and perhaps some steel bands in the
right places.  Better drains in the nearby ground, so it does
not liquify.  The house structure might still be damaged beyond
usability, but it might be less likely to collapse on top of us.

Anybody here know a lot about earthquakes?  Building modeling?
Other crazy stuff to deal with earthquakes?  Somehow, this
rare but massive event seems to generate occasional anxiety
but not a lot of productive planning or design.  

One of the open source apps I would like to see is a distributed
P wave detection system, that aggregates accelerometer data from
laptops and hard drives over the internet, anticipating the
arrival of the slower but more damaging damaging S waves.  If a
megafault earthquake starts a few hundred kilometers away, that
might provide more than 15 seconds of warning, allowing me to get
the heck out of the basement and away from the splintering wood and
flying glass, before the ground movement makes it impossible to run.

Keith

-- 
Keith Lofstrom          keithl at keithl.com         Voice (503)-520-1993
KLIC --- Keith Lofstrom Integrated Circuits --- "Your Ideas in Silicon"
Design Contracting in Bipolar and CMOS - Analog, Digital, and Scan ICs