## PSN-L Email List Message

Subject: Re: plum bob seismometer
From: ian ian@...........
Date: Fri, 17 Nov 2006 10:25:45 +0000

```Hi,

I got my nanos and micros mixed up!  The back of envelope calculation
concluded a movement of 100 micro meters.  So no diffraction patterns
involved, phew!

The email with the formula is in the 2001 archive, Wed, 7 Feb 2001,
subject: "tiltmeter sensitivity".  The assumed distance from the
epicentre was 90 degrees.

No problem with folded pendulums! (or is it pendula?)

Ian

ChrisAtUpw@....... wrote:

> 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

Hi,

I got my nanos and micros mixed up!  The back of envelope calculation
concluded a movement of 100 micro meters.  So no diffraction patterns
involved, phew!

The email with the formula is in the 2001 archive, Wed, 7 Feb 2001,
subject: "tiltmeter sensitivity".  The assumed distance from the
epicentre was 90 degrees.

No problem with folded pendulums! (or is it pendula?)

Ian

ChrisAtUpw@....... wrote:
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

```