
How long should we wait for an overdue earthquake on the San Andreas? - cossatot
http://rocksandwater.net/blog/2016/07/wrightwood-recurrence/
======
fit2rule
I lived in SoCal and worked in SFO for some decades and witnessed both the
Northridge and the Oakland quakes first-hand, narrowly avoiding personal
injury or even death in both cases (big things falling around me), and the
conclusion I made after these events, which I eventually acted on, was simply
put thus: GTFO!

I really didn't want to be there when the Big One happened, nor even some of
the minor small ones, so I've moved to Central Europe where such things have a
lower chance of happening .. in a way, I have a perverse desire to see The Big
One happen from so far away, but I always dread the mind-game of trying to
conceive what SoCal will be like, afterwards. I truly dread the idea, and I
honestly can't understand how any society with scientific awareness of its
surroundings can nevertheless commit to building so much expensive
civilization and infrastructure in a known catastrophe zone. I guess its just
a matter of momentum, but I sure wish the citizenry of the PNW and SoCal would
prepare themselves for this event a bit better. It seems so defeatist to
continue to build things in that area, knowing it could fall into the sea in a
moment, and there is nothing we could do about it. California should just be a
massive nature park stripped of all human involvement, just in case, but of
course this is never going to happen, so if The Big One does happen in my
lifetime, its just going to be a massive tragedy no matter what we humans
could have done about it with all our science and stuff. Argh!

~~~
ghaff
I guess if I lived through two significant earthquakes in that way, I'd
probably have had a thought along the lines of "This is a sign to move" as
well.

>It seems so defeatist to continue to build things in that area

Fatalistic is probably the better word. I can buy an old missile depot in the
Midwest and stock it up with supplies and prepare myself for the zombie
apocalypse or whatever.

Or I can live somewhere I enjoy, and has good opportunities, etc. and not
worry too much about events I don't have a lot of control over or a lot of
insight into their probabilities.

Of course, there are situations between those two extremes and it's not
unreasonable IMO to include "the Big One might hit" into a calculus for
evaluating moving to or staying on the West coast. (As with living in areas
with a lot of potential for floods, hurricanes, and tornadoes.)

Actually turns out Las Vegas, for example, scores pretty well on non-disaster
metrics. One reason a lot of datacenters are there--in addition to evaporative
cooling.

~~~
fit2rule
Its not like I didn't have a great time living in California, because I truly
did, and in many ways its a delightful civilization in which to participate.

Perhaps its just a cultural comfort I seek, in which the citizenry at least
_seem_ aware and prepared for total and utter disaster, any minute now, and
live accordingly. I guess its exhausting to live that way, so if it happens,
it happens; maybe that liberal and - lets just get out and say it, "Zen-"like
mindset truly is just a part of the California love ..

~~~
ghaff
Honestly, though, I'm not sure anyplace in the US is different. I lived in New
Orleans and I was well aware of the hurricane scenarios as well as some of the
failure scenarios of Corps of Engineers structures up the Mississippi. (Had a
good friend who worked for the Corps.)

So it seems a pretty typical attitude in the US. Perhaps it's different
elsewhere. Abstractly understand the worst case scenarios, plan to mitigate
them (or not), but go on living life.

------
brador
Question: what happens to land rights after a quake? Since the quake moves
land around, stretching in parts and destroying land into cracks in others. Do
property lines get redrawn? Who owns any newly created land space? Is it fair
game for anyone to claim?

~~~
celticninja
It doest really work like that, it's not like new land is created by pushing
out into the sea, but even if it was the property owners boundary is likely
the sea, therefore the land is incorporated within their area.

~~~
JshWright
It very much does work like that though... The San Andreas fault is a "strike-
slip" fault. The plates are (effectively) moving past each other, in opposite
directions.

Imagine you owned a rectangular piece of land, with the fault running right up
through the middle of it. After an earthquake, the western half of your
property is now shifted a non-trivial distance to the north relative to the
eastern half. What happens to the property line? Does it now have a 'kink' in
it? Does it remain in the same place relative to the 'ideal' geodesic plane
(meaning various landmark like fenceposts, etc, are now in a different place
relative to the property line).

It's certainly an interesting question...

~~~
evgen
You have ownership of a piece of land, not a spot on a map. If the land moves
then you still own the land even if it is non-contiguous. I am not sure what
happens in the case where some event creates new land adjacent to yours such
as the case where a lava flow extends land out past yours into what was once
water or if an uplift fault raises seabed to become contiguous with yours, but
I would assume that the state would claim ownership over the new land.

~~~
hueving
>You have ownership of a piece of land, not a spot on a map.

That's sort of silly. How do you define a 'piece of land'? What if I dig out
my piece of land so it's a 100ft hole and then there is a sheering motion from
the plates so half of my hole slides under someone else's land? Do I still own
both halves? If so, do I no longer own the land at the bottom of the top half?
If not, then it would not seem that I do not own a 'piece of land'.

~~~
ptaipale
Land ownership is not really absolute; it is always subject to the definitions
of the local law and, ultimately, the whims of the government.

You don't have complete power over what you do to your land, because the
government has the last word. On the other hand, without government, there is
no land ownership because the definition and enforcement of land ownership is
one of the most ultimate functions of any government, since the creation of
first city-states (e.g. ancient Babylon).

So if the government permits you to dig that hole in the first place, then
what happens in an earthquake depends on local legislation. I don't really
know how it works e.g. in the U.S. but I would assume that the boundary of
your piece of land is defined in relation to physical markers that are
recorded with their geocoordinates, but if the lay of the land changes so that
the markers move, then the boundary of your plot will also move. And this
could mean that the size of your plot changes.

Where I live, for instance, there are old boundary stones (which would in an
earthquake naturally move along with the land on which they are laid) and
newer marker bolts attached to bedrock that serve as reference points for
geodesic measurement purposes. Also, there are height markers; for instance,
when I started to build my house, the city would send a guy with equipment and
start from one of these markers and then tell me if the foundations of the
house are at right elevation. Should there be a major earthquake (not really a
possibility here, ours is just about the most stable bedrock on Earth) then
the changed positions (coordinates) would have to be recorded in land
registry.

~~~
GregBuchholz
You may find learning more about the foundations of common-law to be
interesting (since it seems you are from a Civil Law perspective).

[http://faculty.msb.edu/hasnasj/GTWebSite/TortWeb.html](http://faculty.msb.edu/hasnasj/GTWebSite/TortWeb.html)

[http://papers.ssrn.com/sol3/papers.cfm?abstract_id=586941](http://papers.ssrn.com/sol3/papers.cfm?abstract_id=586941)

~~~
ptaipale
Thanks, these were interesting reads, although I would still appreciate a hint
how common law specifically would handle emergence of new land differently
from civil law systems?

------
qrendel
I was under the impression that the bigger danger was the expected eventual
earthquake of the Cascadia Subduction Zone, potentially leading to tens of
thousands killed or injured and millions more displaced.[1][2]

[1] [http://www.newyorker.com/magazine/2015/07/20/the-really-
big-...](http://www.newyorker.com/magazine/2015/07/20/the-really-big-one)

[2]
[https://en.wikipedia.org/wiki/Cascadia_subduction_zone#Earth...](https://en.wikipedia.org/wiki/Cascadia_subduction_zone#Earthquakes)

~~~
cossatot
The damage from a Cascadia rupture is going to be more widespread but the
ground shaking in the metro areas may be less than for the San Andreas because
the San Andreas hits the surface quite close to populated areas (LA also has
more people that WA and OR combined). The intensity of ground shaking
decreases with distance due to geometric spreading and energy absorption by
the intervening rock mass. Cascading ruptures are also every 500 years (or so)
vs every 100 years, so the hazard per year is less. But yes, both are major
concerns.

~~~
int_19h
Also, speaking of other faults, WA also has the smaller, but much more
shallow, Seattle fault. Because it's so much closer to the surface, and right
under the city, it can potentially do more localized damage than Cascadia.

(There are other dangerous faults like that in Puget Sound region, but Seattle
fault gets special attention because of how many densely populated Seattle
metro areas sit literally right on top of it.)

------
rwmj
There's a ton of data on the very regularly occurring (hourly) small
earthquakes around the world available from USGS:
[http://earthquake.usgs.gov/earthquakes/](http://earthquake.usgs.gov/earthquakes/)
I'd like to see whether this analysis works on this rich data, not on the very
sparse data set of San Andreas earthquakes.

------
sveme
Some fault lines seem to accumulate energy, so the longer the waiting period
between two earthquakes, the stronger it gets. Is it the same for San Andreas,
so that more frequent earthquakes would actually be beneficial as they would
be easier to handle structurally?

~~~
tqkxzugoaupvwqr
I’m not an expert and I have the same understanding. Futuristic earthquake
mitigation approaches talk about inducing small, non-destructive earthquakes
in a controlled way to reduce the magnitude. The goal is to completely manage
earthquakes.

~~~
ScottBurson
Not as good an idea as it sounds. The problem is that the largest earthquakes
release massive amounts of energy. Each point on the Richter scale corresponds
to about a factor of 30 in energy. So to release the energy of one magnitude-7
quake would take some 900 magnitude-5 quakes. And a 5 in a populated area can
still do a little damage. Can you imagine how people would feel about having
one of these a week for 20 years?

~~~
MengerSponge
On the other hand, a daily (smallish) earthquake could easily replace your
alarm clock.

"Sorry I'm late... I slept through the tremor this morning."

~~~
Arnt
Time your sex well and you can have (or fake) an earth-shaking orgasm.

------
ZenoArrow
What I can't understand is that after the 1906 San Francisco earthquake, where
"Over 80% of the city was destroyed by the earthquake and fire" (
[https://en.wikipedia.org/wiki/1906_San_Francisco_earthquake](https://en.wikipedia.org/wiki/1906_San_Francisco_earthquake)
), why on earth was it rebuilt? Surely that's a sign to move the new city
elsewhere?

~~~
onion2k
You're only looking at the downside risk. There are _huge_ upsides to the area
- notably the San Francisco Bay is a natural harbor, which makes it a really
good place to put a port. The promise of wealth from trade meant people would
live them pretty much regardless of the downsides.

~~~
ZenoArrow
Fine, but what's likely to be cheaper, building an artificial harbour away
from the fault line or rebuilding a damaged city every 100 years or so?

~~~
onion2k
You'd have to go a _long way_ from the San Francisco Bay to be a safe distance
away from the fault line, which would have a dramatic impact on the costs of
operating the port - it'd add hundreds of miles to the distance you'd need to
move the goods off the ships to where they were needed. Factoring that
additional cost in over the decades between earthquakes (SF burned down quite
regularly prior to 1906), I wouldn't be surprised if it was actually cheaper
to rebuild the city occasionally.

~~~
ZenoArrow
> "You'd have to go a long way from the San Francisco Bay to be a safe
> distance away from the fault line"

Is there an equation that's useful in working out how the strength of an
earthquake changes as you move further away from a fault line? I tried to find
one, but haven't had any luck yet.

------
lordnacho
What does an historic earthquake look like in the layers of rock? How do they
know when they occurred?

~~~
cossatot
The science of finding out the (pre-)historic earthquake history is called
'paleoseismology'. You can read about it from a variety of sources.

In most instances the earthquakes are dated by finding carbon-bearing material
in deposits that look like they were created during the earthquake, and doing
radiocarbon dating of them. The ages may be bracketed by radiocarbon dating of
sediments that were clearly broken by the earthquake (and are therefore older)
and ones that overlie the broken rocks (and are therefore younger).

In a few other instances, earthquakes can be dated by tree-ring dating; for
example during big subduction zone earthquakes, the coast often subsides by a
meter or two, which will put some forested beaches under sea level (or at
least high tide level) and kill all of the trees that can't deal with salt
water.

In others, the dates of sediment layers broken or caused by earthquakes can be
dated through other means, or correlated with climate events of known time.

Some example of deformed and undeformed sediments in the Wrightwood trench
site on the San Andreas is here[0,1]. [2] is from the nearby San Jacinto
fault. [3] has a lot of images. [4] is a good introduction to the science with
good pictures.

[0]:
[http://www.bssaonline.org/content/97/4/1054/F14.large.jpg](http://www.bssaonline.org/content/97/4/1054/F14.large.jpg)
[1]:
[http://www.bssaonline.org/content/92/7/2726/F11.large.jpg](http://www.bssaonline.org/content/92/7/2726/F11.large.jpg)
[2]:
[http://lithosphere.gsapubs.org/content/7/3/211/F6.large.jpg](http://lithosphere.gsapubs.org/content/7/3/211/F6.large.jpg)
[3]:
[http://earthquake.usgs.gov/research/external/reports/04HQGR0...](http://earthquake.usgs.gov/research/external/reports/04HQGR0083.pdf)
[4]:
[http://isites.harvard.edu/fs/docs/icb.topic988563.files/EPS2...](http://isites.harvard.edu/fs/docs/icb.topic988563.files/EPS203_paleoseis5r.pdf)

------
ejcx
So, we aren't only overdue but a quake seems imminent? The upper bound of time
between quakes was very slim.

This is a stupid and selfish question, but what does a quake on the San Andres
fault mean for San Francisco? My knowledge of all of this is based on 4th
grade science.

~~~
celticninja
Bad news. Whilst building codes may be better than in the past, due to
population density the risks of a high number of deaths is significant.

~~~
abalos
I would imagine a very significant portion if the Marina district just turning
into rubble unfortunately. I'm hoping this doesn't happen until buildings have
a chance to improve even more.

~~~
cloudjacker
No chance for improvement. New buildings follow better building codes, such as
the tall ones that may sway like Japanese skyscrapers, old buildings have no
mandate to improve, and San Francisco was mostly built after the 1906
earthquake, with many of the walkups that litter the view being in the 1920s -
1940s.

From my understanding, any hope you might have is neglecting a reality that an
overdue earthquake will cause devastation largely reserved for the third
world.

------
Cortexia
Hopefully San Andreas will wait another 10 years, because by that time there
will be no Nuclear Reactors operating in California. We are down to only ONE,
and it will shut down within the next 6 years. PG&E is getting out of Nukes.

------
sintaxi
If it doesn't happen this year, just wait longer.

~~~
stillworks
winning by induction

~~~
DavidSJ
Subduction actually.

------
Cortexia
People always say Hayward Fault is more troubling for California because so
much is built directly ON the fault.

------
marcosscriven
Possibly a silly question, but...

I hear the term 'overdue' applied particularly to earthquakes, rather than any
other naturally occurring event. Does this mean 'overdue' in the same sense
that rolling a six is 'overdue' if you've not seen one after six rolls?

~~~
gradys
My understanding is that the probability and expected magnitude of an
earthquake actually increases over time as tectonic tension builds. So no, not
like dice.

~~~
marcosscriven
I meant in the sense of probability, not literally like dice :)

~~~
pc86
I think it was clear what you meant.

If you roll a dice 10 times and don't get a six, the probability of rolling a
six is still 1/6 for the next roll. However, as the time since the last
earthquake increases, not only does the probability of one increase (unlike
dice which has a constant probability) but also the likely magnitude of it
increases as well.

The equivalent with dice would be you roll a non-six 10 times in a row, and
instead of 1/6 probability of rolling a six, you now have a 1/3 probability of
rolling a six and a 1/100 probability of setting off a nuclear explosion.

~~~
marcosscriven
Thanks for the helpful response. I still don't think I got quite the question
across that I meant though.

It wasn't so much the probability model (independent or otherwise) I intended
to question (hence my very poor choice of the die rolling analogy), but the
choice of describing an event as 'overdue'.

At the risk of introducing another down-voted analogy, presumably hurricanes
have a probability of occurring based on things like ocean temperature, time
of year etc., but I don't think I've ever heard the phrase 'the east coast of
the US is overdue a hurricane'.

~~~
mercer
The term 'overdue' is used because, as earlier posters explained, the
probability of an earthquake actually increases the longer that it doesn't
happen. But it comes to hurricanes, I suppose the probability of them
occurring does not increase if they don't happen (or we just don't know), and
that's why we (generally) don't use the term overdue.

