Earthquakes
Contents:
- Your Earthquake and You
by laurence/cco.caltech.edu (Dustin Lee Laurence) (18 Jan 1994)
- Your Earthquake and You
by ()
- earthquakes and tank supports
by "Andrew Faust" <andrewfaust/alum.mit.edu> (Sun, 4 Mar 2001)
by laurence/cco.caltech.edu (Dustin Lee Laurence)
Date: 18 Jan 1994
Newsgroup: rec.aquaria,alt.aquaria,sci.aquaria
Here is some e-mail I sent out earlier which might be of some interest
to the net, with updates as my facts improve: :-)
[I am in Pasadena, California, Northeast of Los Angeles proper and
perhaps twenty-five mi (forty km for the rest of the world) west of
the epicenter. I believe 10km is considered quite shallow, and there
may have been more damage than one would expect from an earthquake of
this magnitude because of this. Steve is in Brentwood, West and a bit
South of me and something like South of the epicenter. He is closer
than we are to the epicenter. Yes, I am at Caltech, one of the
national centers for this sort of thing, and no I have no source of
inside info.]
Steve is OK, or at least he was as of 9:00AM. Some statistics, which
those who care probably already know (all of it hearsay of course,
from the news, the net, and whatever):
Summary: (for those who think my posts are a bit long) ;-)
Big quake north of LA at 4:30AM local time, our tank is
undamaged, Steve only had his skimmer fall & dump a lot of
water. We had a few corals fall, Steve had several fall.
Steve lost power, but it was back on as of 9:00AM. Lots of
others weren't so lucky.
Epicenter in Northridge, at 4:31AM PT, magnitude 6.6, duration ~40s
(this of course varies depending on where you are....), on a
previously unknown fault. They felt it as far away as Las Vegas (!),
though apparently SF didn't notice it much. It shook quite hard, and
the motion was jerky enough to show that it was clearly pretty close
(for those who don't know, the motion becomes gentler and more rolling
with distance--ought to be because the higher frequency components are
damped more quickly). This was the second most violent quake I've
been in since we got here, I think, and not much less than the worst.
The epicenter turned out to be something like 10km below the surface
and 25 mi west of us--I haven't looked at a map yet. The main quake
radiated North and South, so we didn't get the full strength.
Unfortunately, that would put it North of Steve, which would mean that
it was not only closer to Steve but he would have gotten a bigger
fraction of the quake. In any event, it shook much harder there.
We just stayed in bed--nothing can fall on the bed but the roof, and
we're on the top floor, so it's about as safe as anything else (well,
OK, not quite). The anti-earthquake stuff worked well, and our tank
only sloshed. A rock or two shifted, no problems. An elegance coral
and a small soft coral did fall, but seem to be OK (good thing that
the flesh is more or less retracted at 4:30AM), and the leather coral
seems to have had a good shaking. Neither Acropora fragment fell,
miraculously. For non-fish stuff, very little fell, just a few things
out of a cupboard and knick-knacks off a couple shelves. Even most of
our books stayed on their shelves.
The power went out throughout a lot of LA, I heard as far as here in
Pasadena, though our power didn't go out at all. Apparently the power
went out some places several states away due to inobvious power grid
topology. Of more immediate concern for the future of Acropora
culture <g> was the fact that the power was out at Steve's.
Apparently Steve's tank made it through the quake OK too, which is a
real miracle--acrylic tanks seem to be very tough in this regard. The
power was out, though. He said that about a minute after the quake he
heard the skimmer fall, and said something about crawling around in
the dark with water pouring out on the floor trying to fix it, and
thinking about what might happen if the power returned and there was a
short somewhere....
At 7:30 or so, Steve called, asking if I knew anyone with a generator.
He was occasionally disturbing the surface by hand. I didn't, and so
we discussed the possibility of my picking up a generator for him. He
called back while I was on the phone with various relatives--the power
came back on at 9:00AM, so he should be fine unless it went out again.
The damage is apparently quite extensive nearer Northridge, and the
last fatality count I heard was 14. That's really quite remarkable,
considering some of the structural damage. Chalk it up to the early
hour, a holiday, and the continuing process of evolution toward more
and more sturdy buildings here. Thank you, Lord.
[[Fatality count up to 29 at least. Steve had another power outage
but is doing fine. I'll ask if I can post his letter.]]
Dustin, "Do I count as an old hand at this yet?"
From: laurence-at-cco.caltech.edu (Dustin Lee Laurence)
Date: 23 Jan 1994 03:19:12 GMT
by
Newsgroup: rec.aquaria,alt.aquaria,sci.aquaria
jason-at-lanai.cs.ucla.edu (Jason Rosenberg) writes:
>Just thought I'd add my two cents. I live in Sierra Madre,
>at the east end of Pasadena, probably about 3 miles further
>from the epicenter than Dustin.
Sometime when we take a trip to Tong's or something we ought to drop
by and pick you up.
>My tank lost a bit of water due to sloshing, and several of the
>rocks shifted.
We had a couple rocks shift too. This is a point I neglected earlier.
A really quake-safe tank should be arranged with quakes in mind.
Maybe next time. I might get some high-test fishing line or something
for the new tank (which I ought to post about sometime).
>This was one of the strongest I've been in, along with the 1989 Loma
>Prieta (I was at Candlestick), and the 1987 Whittier Narrows quake.
There was one stronger than this since we've lived here, which is
about three and a half years now. I think that was our first one, so
it was probably a summer quake a few years ago. I say it was stronger
because we had a few dishes break that time (not to mention that was
the time we made our stupid and death-defying grab to hold all quarter
ton of water and rock as it rocked back and forth....
>I guess it is a good time to summarize the netwisdom on quake
>proofing aquariums. Dustin, can you let us know what you have
>done.
Well, the first time we had a quake the stand (an el cheapo) rocked
back and forth and the tank slid enough so one corner dropped off the
edge of the stand and onto the bottom glass, twisting that end with
respect to the other. I have _no_ idea how a $40 glass tank (55g)
survived that. After that, I got religion about this stuff. My goal
is generally to ensure that the tank can survive any quake that the
building can survive. I don't know if I actually do that, but it's a
nice goal to keep in mind.
I noticed that all aquarium stands are flat surfaces, no lips. All my
stands now have a lip of some kind around the aquarium. I don't think
it requires much strength. You don't have to stop a slide, just stop
it from starting.
I've been told that this is usually not a problem, that tanks don't
usually slide on their stands. Maybe, but I'm not tremendously
impressed with what Angelino's consider an earthquake ready tank.
Also, I know a guy who had a custom 120g bottom-drilled glass tank
which pivoted around the bottom drain in the same earthquake.
Fortunately, the thing only move a few inches. It sat right over his
bed...
The other thing is that an aquarium on a stand is inherently
top-heavy. All quarter ton of water was rocking back and forth from
one set of legs to the other that first time, which sort of makes the
short hairs on the back of your neck stand up on end (I'm sure the
downstairs neighbors wouldn't have enjoyed having it fall on their
roof, either). I think all earthquake ready stands need to be either
super-stable or tied to the wall.
The first approach involves (as I have tried it) padded bumpers
against the wall and some sort of load-bearing structure in front of
it. This is how I re-did the current reef after that first quake. It
isn't pretty. The Forever In Progress stand for the next reef setup
also does this, but instead of an unsightly 2x4 structure in front of
it it has a narrow shelf in front of the tank which covers the second,
lower tank (I posted about this design once, and I think the post is
archived).
For a third tank (nearly on-line, yay) I simply got permission to
drill into the wall. that stand has the bumpers as for the previous
type, but will rely on cable through a large eye screwed into a beam
to stabilize it against tipping forward. I even bought one of the
cable gizmo's to make the cable taut. This one isn't quite finalized,
since we need to do just a bit more plumbing before we finalize the
cable placement.
The thing to keep in mind about this stuff is that it doesn't take
that much to stop the tank from starting to move--that from a
structural engineer. I screwed the eye into a beam because I always
over-engineer unless I have a good reason not to. However, apparently
just using a spreading bolt of some kind to attach the tank to the
paneling/sheetrock/what-have-you between the studs is a great deal
better than nothing at all.
Finally, don't forget about filters and other equipment. Our 5'
skimmer is attached to the stand with one of the brackets which are
meant for holding compressed gas cylinders. I highly recommend these
things for large skimmers (ours is 6" in diameter and fits well).
Steve didn't do anything like this, and while I posted that he
survived the quake his skimmer did fall. If he hadn't been there,
things would have been very bad.
I also recommend thinking about where your pump is. Remember, WATER
WILL SPLASH NO MATTER WHAT YOU DO (unless you have a hermetically
sealed tank). Our pump sits behind the tank and under the stand right
now--that's a bad place, and we'll have to move it. I just hadn't
realized how bad a place it was until I thought about what would
happen if a third of the water sloshed out, as could have happened if
we'd been closer. Scratch a pump, at least.
Dustin
by "Andrew Faust" <andrewfaust/alum.mit.edu>
Date: Sun, 4 Mar 2001
To: <apisto/listbox.com>
</delurk>
What the situation calls for is a structural engineer. I'm an architect,
which is not quite the same thing, but I know that there are a few solutions
used in buildings to maximize life safety and minimize damage in the event
of seismic activity (a.k.a. lateral forces and uplift).
The ideal solution for aquaria, it seems to me, should include some type
of dampening of forces as they transmit themselves thru the building. I
don't know exactly how this could be accomplished with a tank stand, but at
the building scale it is sometimes done with large steel springs and
pneumatics. This is used only in steel and concrete construction, as far as
I know.
Here's an over-simplified explanation (this is actually fairly new
technology and hasn't become standard in construction yet): A building would
have two steel frames. One is rigid, to resist lateral forces - it's
basically a vertical truss of steel columns, beams, and diagonal members,
braced to the ground. The other is more flexible - columns and beams (no
diagonals) which support concrete floors and roof, and the connections
between the members are allowed to 'give' a little, i.e. no moment
resistance. The walls sit on the concrete and are nonstructural. At various
points between the two frames, you put steel disk springs and large
pneumatic shock absorbers. When lateral forces transmit from the ground
through the rigid steel frame, the rigid frame moves but the force is
dampened before being transmitted to the more flexible frame, so the
periodicity of the seismic activity is reduced. Thus the building doesn't
move so much, giving you less damage and more safety.
I imagine a system like this could be developed for tank stands. Perhaps
you make a rigid framework - steel or wood - and anchor it firmly to the
floor and wall. Then you 'float' a shelf on top of the framework, so that
there is minimal friction between it and the frame. Leave space at the edges
and put...oh, say, neoprene padding between the shelf and the vertical
members of the frame. Attach the tank firmly to the shelf somehow.
That might help mitigate the shock of lateral forces.
The only other force you need to be concerned with is uplift, because
earthquakes move in both horizontal and vertical directions. The only thing
you can do about that is make sure the shelf and tank are restrained from
moving upwards somehow - perhaps a piece of wood or steel that runs over the
top surface of the shelf, attached only to the framework. This would allow
the shelf to move in the horizontal direction but not in the vertical.
Unfortunately, seismic engineering hasn't come up with a really
effective way of dealing with uplift, for minimizing damage to buildings. We
can do a pretty good job with lateral forces, and we can deal with life
safety issues in terms of uplift, but damage is just going to happen when
you have one of those rolling up-and-down type of earthquakes. Just keep
things restrained, i.e. tank lids, filters, etc.
Hope this helps!
Andrew
ps welcome to the bay area!
</end delurk>
-----Original Message-----
From: Sarah LeGates <slegates@yahoo.com>
To: apisto@listbox.com <apisto@listbox.com>
Date: Sunday, March 04, 2001 11:14 AM
Subject: Re: earthquakes and tank supports
>Hello all,
>having experienced a couple of small tremors in my new home town in
>the East Bay, I've been giving this issue some thought indeed.
>Someone with a little more experience in physics can correct me if I
>get this wrong, but I would imagine the two big forces we're
>concerned with are inertia and friction, and how our tanks respond to
>the energy input from the quake. The short version is that inertia
>is what makes the water slosh, and friction keeps the tank on the
>stand and the stand in one place on the floor. Someone mentioned in
>an earlier post that one of their tanks moved nearly 2" on its stand
>during a quake, which means that the force of the quake was
>sufficient to overcome the friction between tank and stand and shift
>the tank by that much. I know that under normal circumstances I
>cannot shift any of my tanks when they are full, so you can imagine
>how much force was being applied to that tank and stand during the
>quake. If your tank and stand are both fixed to the wall, the only
>way the force of the quake can be expressed is through water motion,
>and as mike mentioned that force might burst the seams of the tank,
>or if nothing else there will be a lot more sloshed water than if the
>stand alone is anchored. It seems that anchoring the stand is done
>with an eye towards keeping the stand and tank from toppling, since
>the principle of dissipating energy via tank movement would also
>apply to stand movement(though certainly you'll lose much more water
>if the tank falls over!). It was either posted here or on the Krib
>that someone had installed "bumpers" on their stands to keep the tank
>itself from shifting all the way off, which I think is probably a
>better choice than anchoring the tank to the wall with strapping.
>So, do any real physicists out there want to add to my science? It's
>been a while since I took physics...
>
>Cheers from the fault zone,
>
>Sarah LeGates
>
>--- Mike & Diane Wise <apistowise@bewellnet.com> wrote:
>> Daniel,
>>
>> If the tank were firmly anchored, I'd worry about the sides
>> bursting due to the
>> pressure of
>> "sloshing" water. If the tank can move, "give" a little, I'd expect
>> there to be
>> less stress on the glass. Just a thought. Hmm. Aquarium air bag
>> (like in
>> automobiles)?? I wonder if there's a market there? :-)
>>
>
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