Felt report & pendulum picture
Skywise
Was playing couch potato when I noticed the venetian
blinds rattling. Thought it was the cat. Then I thought
it was the wind. Then I noticed that cat was asleep
and the window was closed. Then I realized it was a
big distant quake. I was standing by this point and
stopped for a moment to see if I could feel the ground
moving. No perceptible motion although I felt a bit
of vertigo.
Several months ago I set up a simple pendulum in my
room hanging from the ceiling with the tip in a pan of
sand. Length to center of mass is 61 inches giving a
natural frequency of about 2.5 seconds.
So I ran into my room and sure enough the pendulum
was swinging along. I stopped the pendulum before it
erased the pattern.
A first picture is available at:
http://home.earthlink.net/~skywise711/quakes/pendulum1.jpg
The picture is oriented so that north is at the top.
Brian
Timberwoof
Skywise <in...@oblivion.nothing.com> wrote:
> Felt the quake in Stanton, Orange County.
>
> Was playing couch potato when I noticed the venetian
> blinds rattling. Thought it was the cat. Then I thought
> it was the wind. Then I noticed that cat was asleep
> and the window was closed. Then I realized it was a
> big distant quake. I was standing by this point and
> stopped for a moment to see if I could feel the ground
> moving. No perceptible motion although I felt a bit
> of vertigo.
Do you normally not feel vertigo when you stand up from the couch?
> Several months ago I set up a simple pendulum in my
> room hanging from the ceiling with the tip in a pan of
> sand. Length to center of mass is 61 inches giving a
> natural frequency of about 2.5 seconds.
>
> So I ran into my room and sure enough the pendulum
> was swinging along. I stopped the pendulum before it
> erased the pattern.
>
> A first picture is available at:
>
> http://home.earthlink.net/~skywise711/quakes/pendulum1.jpg
>
> The picture is oriented so that north is at the top.
That's very cool. How big is that dish?
I'm confused about something. There are two sets of waves recorded,
quite nicely at right angles to one another. That would correlate to the
P- and S- waves of a distant earthquake, with the Ssecondary-wave
tracess overwriting the Primary-wave traces.
P waves are "Primary" and, as it turns out, "Prerssure": moving radially
back and forth along a radius away from the center. S waves are
"Secondary" and "Sideways" -- at right angles to a radius away from the
center. (There's a nice picture at
http://earthquake.usgs.gov/4kids/games/coloring/waves.pdf .) P-waves
travel faster through rock than S-waves, and so arriive first.
So here's why I'm confused. I would interpret the trace in your picture
as showing the epicenter along a line E-NE / W-SW. But
http://quake.usgs.gov/recenteqs/latest.htm places that big one at W-NW
of your location.
Maybe you recorded a different earthquake? Maybe I'm wrong about how a
pendulum would record an earthquake?
--
Timberwoof <me at timberwoof dot com>
http://www.timberwoof.com
Hatunen
<timbe...@stimpberawoofm.com> wrote:
>P waves are "Primary" and, as it turns out, "Prerssure": moving radially
>back and forth along a radius away from the center. S waves are
>"Secondary" and "Sideways" --
"Shear"
************* DAVE HATUNEN (hat...@cox.net) *************
* Tucson Arizona, out where the cacti grow *
* My typos & mispellings are intentional copyright traps *
Bob Officer
I hope you will be posting more of the patterns from the after shocks.
--
Aktohdi
Skywise
1C90D4.201...@typhoon.sonic.net:
> In article <Xns94597D747A083in...@207.217.77.206>,
> Skywise <in...@oblivion.nothing.com> wrote:
>
>> Felt the quake in Stanton, Orange County.
>>
>> Was playing couch potato when I noticed the venetian
>> blinds rattling. Thought it was the cat. Then I thought
>> it was the wind. Then I noticed that cat was asleep
>> and the window was closed. Then I realized it was a
>> big distant quake. I was standing by this point and
>> stopped for a moment to see if I could feel the ground
>> moving. No perceptible motion although I felt a bit
>> of vertigo.
>
> Do you normally not feel vertigo when you stand up from the couch?
Not normally, no. And when I noticed the sensation I had
already been standing for at least 15 seconds. When I
have felt vertigo from standing too quickly it is always
immediately and lasts but a few seconds. So I doubt the
sensation was from somethign other than the quake.
To be more precise, perhaps vertigo is not the exact
word. I had a sensation of motion but could not visually
see any motion. 'quakesickness'?
>
>> Several months ago I set up a simple pendulum in my
>> room hanging from the ceiling with the tip in a pan of
>> sand. Length to center of mass is 61 inches giving a
>> natural frequency of about 2.5 seconds.
>>
>> So I ran into my room and sure enough the pendulum
>> was swinging along. I stopped the pendulum before it
>> erased the pattern.
>>
>> A first picture is available at:
>>
>> http://home.earthlink.net/~skywise711/quakes/pendulum1.jpg
>>
>> The picture is oriented so that north is at the top.
>
> That's very cool. How big is that dish?
As trimmed in the picture, 6 inches across. I will be
taking better pictures with a scale soon.
> I'm confused about something. There are two sets of waves recorded,
> quite nicely at right angles to one another. That would correlate to the
> P- and S- waves of a distant earthquake, with the Ssecondary-wave
> tracess overwriting the Primary-wave traces.
BTW, I stopped the pendulum as soon as I got to it so it would not
over-write itself too much.
>
> P waves are "Primary" and, as it turns out, "Prerssure": moving radially
> back and forth along a radius away from the center. S waves are
> "Secondary" and "Sideways" -- at right angles to a radius away from the
> center. (There's a nice picture at
> http://earthquake.usgs.gov/4kids/games/coloring/waves.pdf .) P-waves
> travel faster through rock than S-waves, and so arriive first.
>
> So here's why I'm confused. I would interpret the trace in your picture
> as showing the epicenter along a line E-NE / W-SW. But
> http://quake.usgs.gov/recenteqs/latest.htm places that big one at W-NW
> of your location.
The first traces in the sand are along a line 60 degrees from
north-south. If the pendulum indicated the direction to the
epicenter, then the epicenter would either be along that line
or perpendicuar to it. That means the quake could be in one
of four directions from me: 60, 150, 240, or 330 degrees.
From my location the epicenter is 221 miles away on an azimuth
of 315.6 degreees. Assuming 330 degrees leaves a 15 degree error.
Actually, the traces reflect the ground motion at my location.
When the P waves arrived the horizontal motions of the ground
were along that 60 degree line. These motions are a reflection
of the direction in which the fault plane moved.
>
> Maybe you recorded a different earthquake? Maybe I'm wrong about how a
> pendulum would record an earthquake?
>
No, it was definately the 6.5 quake because the pendulum was still
moving when I examined it less that a minute after the quake. This
is the first time the pendulum has moved by something other than
the wind or me bumping it.
Brian
Bob Officer
I would also suggest placing a compass indication around the rim.
Something with 5 degree increments would work.
>> I'm confused about something. There are two sets of waves recorded,
>> quite nicely at right angles to one another. That would correlate to the
>> P- and S- waves of a distant earthquake, with the Ssecondary-wave
>> tracess overwriting the Primary-wave traces.
>
>BTW, I stopped the pendulum as soon as I got to it so it would not
>over-write itself too much.
It worked. Maybe next time have several dishes to place new "recording
medium available, to record after shocks.
>> P waves are "Primary" and, as it turns out, "Prerssure": moving radially
>> back and forth along a radius away from the center. S waves are
>> "Secondary" and "Sideways" -- at right angles to a radius away from the
>> center. (There's a nice picture at
>> http://earthquake.usgs.gov/4kids/games/coloring/waves.pdf .) P-waves
>> travel faster through rock than S-waves, and so arriive first.
>>
>> So here's why I'm confused. I would interpret the trace in your picture
>> as showing the epicenter along a line E-NE / W-SW. But
>> http://quake.usgs.gov/recenteqs/latest.htm places that big one at W-NW
>> of your location.
>
>The first traces in the sand are along a line 60 degrees from
>north-south. If the pendulum indicated the direction to the
>epicenter, then the epicenter would either be along that line
>or perpendicuar to it. That means the quake could be in one
>of four directions from me: 60, 150, 240, or 330 degrees.
>
>From my location the epicenter is 221 miles away on an azimuth
>of 315.6 degreees. Assuming 330 degrees leaves a 15 degree error.
Still not bad. Oh to be a science teacher with such a recording device. It
might spark an interest in science.
>Actually, the traces reflect the ground motion at my location.
>When the P waves arrived the horizontal motions of the ground
>were along that 60 degree line. These motions are a reflection
>of the direction in which the fault plane moved.
>>
>> Maybe you recorded a different earthquake? Maybe I'm wrong about how a
>> pendulum would record an earthquake?
>
>No, it was definately the 6.5 quake because the pendulum was still
>moving when I examined it less that a minute after the quake. This
>is the first time the pendulum has moved by something other than
>the wind or me bumping it.
It might be nice to make a picture of your set up.
--
Aktohdi
Skywise
news:q1qfuv8dnmme1spdb...@4ax.com:
<Snipola>
>
> I hope you will be posting more of the patterns from the after shocks.
>
>
I had not planned for the requirement of replacing the dish. The
one I have has been removed am looking for ways of preserving
the sand permanently.
None of the aftershocks have been strong enough to feel from 221
miles away and I doubt they would have done much to the pendulum.
As it is right now I do not have any sand under the pendulum. Need
to buy more.
Brian
Skywise
<Snipola>
>>As trimmed in the picture, 6 inches across. I will be
>>taking better pictures with a scale soon.
>
> I would also suggest placing a compass indication around the rim.
> Something with 5 degree increments would work.
I can add in a compass circle easily with image editing. Right
now the dish has been removed. I have marked north in the sand
so I know it's orientation.
<Snipola>
>>BTW, I stopped the pendulum as soon as I got to it so it would not
>>over-write itself too much.
>
> It worked. Maybe next time have several dishes to place new "recording
> medium available, to record after shocks.
Since I need to buy more sand to make a new dish anyway, I will
keep this idea in mind.
<Snipola>
> It might be nice to make a picture of your set up.
In lieue of a picture, for the moment here's a description.
The string is 24 gauge electronics wire hung with a thumbtack in
the ceiling. The weight is a short fat bolt with a ball of clay
wrapped around it. The point is a broken toothpick poked into
the bottom of the clay ball. The sand tray rests on a contraption
made from Lego's to raise and lower the tray without moving the
pendulum.
Brian
Bob Officer
<in...@oblivion.nothing.com> wrote:
>Bob Officer <bobofficers...@earthlink.net> wrote in
>news:q1qfuv8dnmme1spdb...@4ax.com:
>
><Snipola>
>>
>> I hope you will be posting more of the patterns from the after shocks.
>>
>>
>
>I had not planned for the requirement of replacing the dish. The
>one I have has been removed am looking for ways of preserving
>the sand permanently.
Spray glue/fixative/?
>None of the aftershocks have been strong enough to feel from 221
>miles away and I doubt they would have done much to the pendulum.
OK.
>As it is right now I do not have any sand under the pendulum. Need
>to buy more.
I wish they were still shipping the brown "hourglass sand" to Mexico.
I might be able to get a hold of several pounds of White silica sand from
Ione. would that help?
--
Aktohdi
Stan
Bob Officer <Ihat...@no-domain.no.mail@no-net> wrote:
>On Wed, 24 Dec 2003 05:27:45 GMT, in sci.geo.earthquakes, Skywise
><in...@oblivion.nothing.com> wrote:
>
>>I had not planned for the requirement of replacing the dish. The
>>one I have has been removed am looking for ways of preserving
>>the sand permanently.
>
>Spray glue/fixative/?
Look up how model railroaders fix the ballast on their tracks.
--
Stan Schwarz | Extreme sports...offer "some kind of physical
http://cosmo.pasadena.ca.us | analog to the thrill of installing Linux or
| other open-source operating systems."
| -Mikki Halpin, _The Geek Handbook_
Roger Hunter
This whole sand business is a homemade version of a strong motion
seismometer.
They used to record on a smoked glass disk.
You need some kind of motion damping to keep the pendulum from
swinging after the quake stops.
One thought for a recording medium would be the paper they use on a
helicorder.
It's black paper covered by a white wax. Any scratch shows up as a
black line.
Roger
Timberwoof
Skywise <in...@oblivion.nothing.com> wrote:
> Bob Officer <bobofficers...@earthlink.net> wrote in
> news:q1qfuv8dnmme1spdb...@4ax.com:
>
> <Snipola>
> >
> > I hope you will be posting more of the patterns from the after shocks.
> >
> >
>
> I had not planned for the requirement of replacing the dish. The
> one I have has been removed am looking for ways of preserving
> the sand permanently.
Mix up plaster, as thin as will still harden. (Experiment on ither
dishes of sand.)
Timberwoof
rog...@Access4Less.net (Roger Hunter) wrote:
> This whole sand business is a homemade version of a strong motion
> seismometer.
>
> They used to record on a smoked glass disk.
>
> You need some kind of motion damping to keep the pendulum from
> swinging after the quake stops.
Attach two flattened spoons or something that are dipped into a jar of
mineral oil. The spoons should be at right angles so the damping effect
is the same in both planes. The viscosity of the oil will damp the
motion. You will have to experiment with the size of the "spoons", the
size of the container, and the thickness of the oil. I'd use baby oil
and specifically not any automotive oil. The latter smells bad and
probably has stuff in it you wouldn't want floating around the air.
Skywise
that have been posted. As soon as the holidays
are over I'll start experimenting with my left
over sand.
As for more sand, I can get it the same place
as before, a local craft shop....or the beach?
Happy Holidays to all!
Brian
Ben Snow
"Skywise" <in...@oblivion.nothing.com> wrote in message
news:Xns945BC5B13B272in...@207.217.77.203...
Skywise
news:ICZRb.7346$cI3....@newssvr29.news.prodigy.com:
> Try diatomaceous earth from any pool supply store.
<Snipola>
Interesting idea. I just happen to have some DE on hand.
It's raw unprocessed DE for gardening use as opposed to
the stuff for pools which has been processed and mixed
with other ingredients.
Brian
Bob Officer
Brian I will be making a trip to Ione, Ca to get some of the fine white
silica sand used in making clear glass bottles in a few weeks. I could get
enough to UPS you enough. 12-16 oz should be enough?
--
Aktohdi