PSN-L Email List Message

Subject: Newcomer questions
From: Brett Collars brettc@............
Date: Sun, 13 Aug 2000 05:59:44 -1000 (HST)


First and foremost as a newcomer I would like to sincerely thank Larry for
the wonderful website that I have throughly perused over the past week, as
well as the numerous and significant contributions to amateur seismology
he has obviously made over the past years - you've got passion Larry ! 

I live in Tokyo and have recently taken a keen interest (via "applied
experiential observation") in seismology. I now want to build a
seismograph to further explore.

I will undoubtedly use Larry's hardware and software (order forthcoming)
but first I need to establish the probabilty that I can succeed in
building an effective sensor given my resources and site location at home.
I have a few questions which hopefully you can help to answer:

1. Soil - the site is my (rented) home in Meguro-ku, Tokyo. I do not
believe it to be ideal as the soil column is "mushy" from a geological
point of view. The best (approximate) column stratification data I can get

0m-1m - fill soil
2m-7m - volcanic ash clay 
8m-10m - clay
11m-20m - gravel
20m - ... (??) rock 

I'm sure solid bedrock would be much better, and I cannot change my site
(nor use the basement at work), so I guess what I am asking is "Would my
soil column pose a serious degradation ?" From what I gather the soil
conditions at my home are perfect for "liquification" and could add
persistence or ringing to seismic wave activity - surely this might
exhibit itself in a seismic sensor I assume (not to mention collapsing
the house during the big one).

2. Background noise - I have a small roadway (~3m wide) next to my house.
Auto and truck traffic is relatively light, slow, and in Japanese fashion
very quiet (aurally). I am concerned however about the proximity of 
the roadway (~1-2m) to the sensor's potential site on my concrete "back
porch". More bothersome is a railway located about 50m from the house. The
railway is elevated 15m above ground on steel encased concrete pillars (EQ
proofed). The rails are welded (no seams) and the train cars are DC
electric powered (should I also worry about EMI ?). The trains run on 3-4
minute intervals and are very quiet and cannot be heard or felt inside the
house. I do not feel any vibration on the grounds surrounding my home or
underneath the railway, and only by placing my hand on the support columns
of the railway can I feel a relatively "medium" transmission of the
passing trains vibration. 

I plan on assessing this background noise by obtaining a 4.5hz geophone
and mounting it at the potential site, connecting the (raw) output to a
single channel of a digital storage o-scope, and by connecting the second
channel of the scope to a microphone comparing the seismic noise to the
airborne noise of the passing vehicles to identify any related noise. I
then plan on passing the geophone signal through a 10hz low pass to get
measurement of what the relative noise level in the band would be. I would
then relocate the geophone to a friend's "quiet" home several km away and
repeat the measurement. I am hoping to obtain an average noise value that
could be applied as the baseline for the nominal recognition differential
at my site (assuming I record a few events for comparison). Does this
approach have any validity ?

3. Sensor - I would like to build a Lehman or SG but more easily practible
I am thinking about a 1HZ geophone, either the HS-10-1 (from the Mitcham
place) or purchasing a horizontal DS-1 from Geospace. I realistically do
not have time nor the location (space is at a premium here) for a Lehman,
and if I built an SG it would have to be of rugid build as it would be
located on the porch outside. The specific questions:

- Has anyone used the DS-1 from Geospace ? It seems it would be ideal
for me as it is small, can be easily weatherproofed, and would not require
construction. I am concerned that it would be very sensitive to noise and
less sensitive to distant seismic waves.
- Would a vacuum enclosed SG eliminate the temperature and "draft"
problems ?

I would like to get the sensor correct from the beginning as I plan to
have a N-S,E-W, and vertical eventually (all of the same design ).

4. Sofware - I have a 128kb dedicated connection to the Internet at
home and would like to view my seismograph from work by taking the output
from SDR, converting it to GIF, and throwing into a web page 
automatically. I have both Windows (2000) and UNIX (Solaris/SPARC). Any
ideas on this ?

Any help or discussion would be most appreciated.


I do not have a basement nor crawlspace to locate the sensor. 





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Larry Cochrane <cochrane@..............>