PSN-L Email List Message

Subject: Re: Vertical design
From: hammond hammond@...........
Date: Sat, 21 Dec 2002 12:04:11 -0900

Chris, with regard to your comments on vertical seismometers, I invite you 
to visit my web page  and specifically look at "earthquakes recorded at 
station GSV" at  Every earthquake I record and display 
is using a Mark Products
L4 1Hz short-period vertical seismometer.  Surely, you  must be joking that 
short period vertical
seismometers are of limited use!


Bob Hammond
Public Seismic Network - Alaska

At 11:38 AM 12/21/2002, you wrote:
>Hi Chris, Jim and all other interested partys,
>That was a very good summation Chris.  Perhaps, however, the
>best use of a vertical is predominately for simply getting the earliest
>phases of any quake/event, with the longest period (p thru s) of
>roughly up to, 3-4-5 seconds.  Of course a longer period vertical
>than that would likely sense those signals best.   Most verticals are
>predominately used for just that aspect in realtity, which is why
>the professionals pursue their use so heavily.  In the PSN amateur
>related sense, and from the horizontal seismomograms presented;
>one often sees the designated "p", somewhere to the left of any
>obvious significant quake induced activity trace deflections....they
>just CAN'T sense the vertical phase quake components.  All
>of this just leads up to the "need" for a vertical of some design in the
>individuals amateur seismometer setting.....perhaps to the extent
>of its value over and above the use of a horizontal seismometer.
>I'am dubious that a broadband vertical with all their problems
>is really all that worthy of the effort involved, when it comes down
>to the more practical short period phases that are actually "read";
>in the general amateur (and likely the professional) realm.  On the
>other hand, I don't have a broadband vertical, so, perhaps my
>thought judgement isn't really totally accurate for their use.
>It might just be, that any one design should incorporate the best
>aspects of other previously proven function pieces and parts.
>A big problem arises when it seems that some of the best use
>or functional pieces/parts are in themselves fairly mechanically
>complicated when addressed to a likely majority of ill-equipped
>individual readers and their own capabilities for its completion.
>I guess I'am always hopeful that there exists some simpler or
>better way to do things, than how some of  the present designs
>are laid out.
>It may well be that Sean's vertical design (SM) could also be
>construed in a variety of degrees (amateur/professional) of
>approach; to satisfy any existing variety of potential use;
>simply by utilizing the base designed mechanics for other less
>sensitive sensor adoptions.  This has apparently been done
>(implied in past PSN emails) in the past by others, or suggested
>but I'am not aware of their success in doing so, at the moment.
>Take care, Meredith
>ChrisAtUpw@....... wrote:
>>Hi Meredith,
>>       Short period verticals are not too difficult to make, but they are 
>> of somewhat limited use. There are a number of practical / engineering 
>> constraints. I note that at least one design uses the U Alnico magnet as 
>> the seismic mass on the end of the arm. This is not a good idea and it 
>> will react to environmental changes in the local magnetic field. In the 
>> normal home, you are likely to see a very noisy trace. It is quite easy 
>> to damp a seismometer using readily available NdBFe magnets. Fluid 
>> damping is very temperature sensitive and can be quite messy. The much 
>> higher field supplied by NdBFe magnets can also be used to increase the 
>> output of coil detector systems and improve their range and linearity. A 
>> survey of a range of systems can be found at 
>> Prof.Braile's link may be found by removing the seismometer reference.


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