Friday, August 14, 2015

Earthquake Stupidity #2 -- Early warning systems

Early warning systems are a seismologist's wet dream.  Remember that these guys can't do math, and have no concept how shaking damages things.  All they know is that these systems bring in lots of money, and they lobby the politicians relentlessly.  Any money for this is taken out of strong ground motion recording.

They work like this:  In an ideal world, you have a tiny fault rupture, at a pinpoint.  It emits seismic waves, and is detected by seismometers, hopefully underwater for the Cascades.  Your super-smart hardware, programmed by super-smart seismologists instantly characterizes the earthquake, giving the PGV at given distances.  If it is going to cause damage to bullet trains and such, it gives a warning to all and their dogs, allowing them to totally save themselves before the actual shear body waves hit.  This miracle is achieved through the magic of physics, in that the seismic waves are slower than the Internet.

Perhaps some of you smart ones begin to perceive the holes in this logic, but if you were that smart you wouldn't be reading this, you'd be writing it.  :)

The system has an open-ended cost.  You can be super-cheap for a few million, or you can go full-hog.  For maximum efficiency you have to predict the exact earthquake you wish to catch.

Now, here's where physics starts to interfere with dreams.  First of all, none of these people know about PGV, it's all PGA.  That's the first horrendous mistake.  But we must look at the grandaddy of such systems - Mexico City, where I have planned my stopover for my next trip, because I didn't want to stop at an American City, where people walk down the streets with assault rifles.  Those big Mexican drug kings don't shoot where they eat.  :)

Those smart Mexicans have planned for the exact same earthquake that hit them before.  It was an M8 on the subduction zone far, far away from the city.  There is no chance for any other type of earthquake -- maybe.  That earthquake produced 20 cm/s on the shore and didn't damage any steam plants.  By the time it hit the city, it was about 5 cm/s on rock.  The whole city is on a really weird basin that not only focusses seismic waves for the rock, but then jiggles like jello on the soft soil.  If you just consider PGV, it amplifies by a factor of 100.

It knocked down a lot of cheap government pancake concrete buildings, but didn't touch the bank towers.  They now have an early warning system that nobody can access, but many are working on that.  Let's assume that soon everybody+dog gets the warning "You're about to die!".  What do they do?

So, we got that problem, but what goes into the 'Die!' message?  The seismometers have to pick up the motions, which is difficult because they clip for large earthquakes.  Then they must determine the size.  For a regular earthquake, this takes a long time, since you must get information from around the world, and the seismic waves take a while to get there.  Unless you predict 'exactly' what the fault rupture is going to do, you can't do it.  Fault ruptures are horribly complex things, starting, stopping, putting out little motion, and then a lot.

So that means a lot of false alarms.  Think of the guy on the Portland beach.  He gets the 'Die Sucka' warning.  He phones his wife "Sorry, take care of my two other mistresses, and my bastard children."  Boy is he going to be mad if it's a false alarm!

Think of cell phones when this message goes out.  The first few people are instantly going to phone other people, the whole system will die before the earthquake even hits.  Wow.

Well, there's whole bunch of other things, and there is no real benefit.  You don't think trains can't take a lateral hit?  Is it worth turning off the power grid?  And there's the fact that the next earthquake won't be exactly as predicted, it's all useless for the one right under the basin.

This is also a stupidity that will get a lot of people killed because it instils a moral hazard.  Why do anything else when you are protected by a warning system?  Japan fell into that one for Kobe.

That's enough, I'm getting depressed....

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