## PSN-L Email List Message

Subject: Re: plum bob seismometer
From: ChrisAtUpw@.......
Date: Thu, 16 Nov 2006 17:51:03 EST

```In a message dated 2006/11/16, ian@........... writes:

> Referring back to some emails from Sean-Thomas on the psn email archive,
> circa 2000, he provided a formula for the relationship between telesiemic quake
> magnitudes and ground tilt. In the example discussed, I think an Ms 6.2
> produced a local ground tilt of 100 micro radians. Doing a quick "back of an
> envelope" calculation, a 1 meter long plum bob would move by about 100 nano
> meters at the tip.

Hi Ian,

At what range from the epicentre?
Do you have the reference?
Remember that you have the microseismic background giving from 500 to
15,000 nm movement? most often 1,000 to 2,000 nm?

> You could get one of those glass columns (from somewhere!) to house it in
> and seal it.  You might employ some form of galvanic spot meter type optics to
> magnify the movement.

You might start having difficulties here. The wavelength of visible
light is about 500 nm, so you would be trying to see a slowly moving diffraction
pattern in amongst much larger microseism movements.....

> It all starts to sound like more effort than a standard Lehman...

Er, how about a nice folded pendulum?

Regards,

Chris Chapman
In a me=
ssage dated 2006/11/16, ian@........... writes:

Referring back to some emails f=
rom Sean-Thomas on the psn email archive, circa 2000, he provided a formula=20=
for the relationship between telesiemic quake magnitudes and ground tilt. In=
the example discussed, I think an Ms 6.2 produced a local ground tilt of 10=
0 micro radians. Doing a quick "back of an envelope" calculation, a 1 meter=20=
long plum bob would move by about 100 nano meters at the tip.

Hi Ian,

At what range from the epicentre?
Do you have the reference?
Remember that you have the microseismic=
background giving from 500 to 15,000 nm movement? most often 1,000 to 2,000=
nm?

You could get one of those glas=
s columns (from somewhere!) to house it in and seal it.  You might empl=
oy some form of galvanic spot meter type optics to magnify the movement.

You might start having difficulties her=
e. The wavelength of visible light is about 500 nm, so you would be trying t=
o see a slowly moving diffraction pattern in amongst much larger microseism=20=
movements.....

It all starts to sound like mor=
e effort than a standard Lehman...

Er, how about a nice folded pendulum?=20=

Regards,

Chris Chapman
```