[SystemSafety] Earthquake Safety
Peter Bernard Ladkin
ladkin at causalis.com
Fri Aug 26 14:31:58 CEST 2016
Still on safety, somewhat further away from "traditional" system safety, but we are still talking
engineered systems and we are talking their safety. A lot of what we talk about has arisen in this
East Latium has just suffered a magnitude 6.2 earthquake, which has destroyed many buildings in what
are described as medieval towns and villages, and caused a sad toll of some 300 deaths.
I sat out a bunch of magnitude-5+ quakes and one magnitude 6.9 during my time in Northern California
https://en.wikipedia.org/wiki/List_of_earthquakes_in_California . Mostly, they don't cause much
damage, except for the 1989 Loma Prieta quake which caused some 63 deaths, 40% of them in a
collapsed double-decker freeway segment in Oakland.
People are apparently saying that strong earthquakes in East Latium are known, even regular, so why
wasn't more done? For example,
Some clue must surely lie in that word "medieval". The towns now suffering had not suffered this
kind of event for over half a millenium. Then, tragic as it is, the level of human death and injury
is not necessarily very high. Amatrice was said to have received some 2,500 visitors in anticipation
of a festival this weekend. If we take it that about 300 people have died (it could well be more),
then that is less than 10% of those present in the town at the time. So, say you live there. You
have a 1-in-10 chance of dying in a 500-year event. That's a 1-in-5,000 chance per year. Is that so
Road-death rate in Italy is apparently around 6 per 100,000 inhabitants per year
That's a 1-in-17,000 chance per year.
So if you live in susceptible villages, you have apparently about three times the chance of dying in
an earthquake as you do of dying on the road. I'd say it's comparable.
A second issue lies in the difficulty of mitigation. The buildings are mostly masonry, which has
awful properties when it gets shaken heavily. Binding it with steel bands and sealing the surfaces
with some magic plastic could probably help a lot, but would look moderately ugly and cost huge
amounts of money. California can do earthquake-protection because (a) it's mostly new-build on (b)
well-spaced property, and (c) mostly wood-build in private dwellings (boy, do they shake! It's like
being in a tree. Where, incidentally, John Muir was during the Lone Pine earthquake to observe the
collapse of one of Yosemite Valley's pinnacles. What a ride that must have been!) and (d) has had
earthquake-mitigation standards for much of its building history. Whereas earthquake safety up until
the twentieth century in places such as Italy was mostly a matter of pleading with the deity to
choose your neighbors rather than you.
Compounding the difficulty is the engineering science. We don't know what goes on in terms of
movement during earthquakes.
That collapsed freeway section in Oakland was dismantled, except for one support structure left
standing for engineers to perform experiments and tests, because it turns out that the motion of the
structure due to the properties of the ground had been incorrectly anticipated - "entirely
misunderstood" might be a better way of putting it.
Other local shear motions have also historically not been well understood. In the 1979 6.4-magnitude
Imperial Valley earthquake, the eight-year-old Imperial County Services Building in El Centro, a
largish building which was not only built to contemporary standards but also heavily instrumented,
was damaged to the point at which it had to be demolished. It turns out that momentary
accelerations, impulses, are larger than thought. "Supershear" rupture was inferred of the Imperial
The 13th century campanile in Amatrice was left standing and mostly intact I believe, whereas the
school building nearby, which was earthquake-mitigation-modified in 2012, collapsed. Of course,
something could have been done wrong, but it's much more likely that, well, that kind of thing just
happens because we don't understand the dynamics very well.
A third issue is resources. It is surely infeasible to earthquake-proof all susceptible towns and
villages: time, effort, and corresponding cost would be beyond any resources which could be made
available. Of course, *something* could be done with any amount of resources. But you would have to
choose where the need is greatest - and, despite the attempts of the Italian judiciary to prosecute
earthquake predictors after the L'Aquila earthquake, you can't say where the next quake is going to
hit or when.
Also, there is competition for those same resources for saving lives - improving roads, vehicle
inspections and speed control; improving health-care-system performance; improving social welfare
for those most in need; fishing people out of the Mediterranean. Much of that competition has a more
deterministic relation between action and result than earthquake-proofing, so there is a more direct
relation between money spent and lives saved.
Prof. Peter Bernard Ladkin, Bielefeld, Germany
Je suis Charlie
Tel+msg +49 (0)521 880 7319 www.rvs-bi.de
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