PSN-L Email List Message

Subject: Re: Caution on low pass filtering emphasis
From: THOMAS DICK dickthomas01@.............
Date: Sun, 03 Jan 2010 14:22:01 -0500


Roger=2C
I am out of town right now=2E I thought you were in Monroe LA =2E=2E=2EC=
ould we talk by direct email=3F Mine is dickthomas01=40insightbb=2Ecom=2E=
 I will get back late Monday=2E =


----- Original Message -----
From=3A Brett Nordgren =3Cbrett3nt=40bnordgren=2Eorg=3E
Date=3A Saturday=2C January 2=2C 2010 11=3A23
Subject=3A Re=3A Caution on=A0 low pass filtering emphasis
To=3A psn-l=40webtronics=2Ecom

=3E Hi Roger=2C
=3E =

=3E At 09=3A37 PM 1/1/2010 -0800=2C you wrote=3A
=3E =3EHello Thomas=2C
=3E =3E
=3E =3EI took a look before and after the quake but did not see =

=3E anything unusual=2E
=3E =3E
=3E =3ENot unusual for this location is to have a fuzzy trace (=7E1 Hz =

=3E High Pass) =

=3E =3Ebeginning about 0630 and ending about 1700 local times=2E=A0 =

=3E Since I am using =

=3E =3Ea vertical=2C I have attributed this to the sun warming the =

=3E =3Eatmosphere=2E=A0 But=2C the noise does not seem to be present =

=3E during non-work =

=3E =3Edays which is completely inconsistent with a solar source=2E
=3E =

=3E Your description could almost be the definition for man-made=2C so =

=3E called =

=3E cultural noise=2E=A0 Natural phenomena=2C though some might drop =

=3E at night=2C aren=27t =

=3E usually affected by weekends and holidays=2E
=3E =

=3E =3E=A0 I live about 2 miles from any serious auto traffic which =

=3E would be on =

=3E =3E I-90 in Central Washington=2E=A0 I have no explanation for =

=3E this =22fuzz=22
=3E =

=3E I think that you are almost certainly seeing truck traffic on =

=3E the =

=3E Interstate=2E=A0 2 miles is plenty close for a sensitive instrument=2E=

=3E =

=3E =3EThe =22fuzz=22 is not visible with either the all pass or low pas=
s =

=3E filters in =

=3E =3Eplace=2E
=3E =3E
=3E =3EOne puzzle here is that in the past I could get a fairly clean =

=3E FFT peak at =

=3E =3Eabout 6 seconds and little at longer periods=2E=A0 Lately=2C I =

=3E notice a broader =

=3E =3Epeak at 6 seconds and a second peak as low as 44 seconds (both =

=3E very broad =

=3E =3Epeaks)=2E=A0 I took a look at about 4 hours of data a few =

=3E moments ago and =

=3E =3Econfirmed what I had previously found=2E=A0 Would we be seeing =

=3E the same thing=3F
=3E =

=3E The 6-second microseism peak is constantly changing=2C so =

=3E changes=A0 there are =

=3E not that surprising=2E
=3E =

=3E I agree that the low frequency peak might very well be the =

=3E atmospheric =

=3E stuff proposed by Chris=2C though verticals are mostly immune to =

=3E the =

=3E wind-caused ground tilting that is so annoying with =

=3E horizontals=2E=A0 His =

=3E question about the pressure cover is a good one=2E=A0 Normally =

=3E the atmospheric =

=3E noise we see on the vertical is in the frequency range of =

=3E minutes and is =

=3E reduced by a factor of 10 or 20 by adding a sealed cover=2E=A0 =

=3E If your vertical =

=3E is small enough to be covered by a cooking pot=2C that would work =

=3E nicely=2E=A0 A =

=3E typical setup would be a very solid base slab=2C like 2-4=22 thick =

=3E granite=A0 with an inverted pot or similar container sealed =

=3E down over =

=3E it=2E=A0 The granite base is because pressure changes will =

=3E cause anything much =

=3E less solid to flex under the seismo and generate noise=2E=A0 =

=3E Our experience was =

=3E that 3/4=22 aluminum flexes way too much=2E=A0 For sealing =

=3E things=2C including =

=3E cable openings=2C Dave Nelson has found that the putty-like =

=3E windshield =

=3E sealant seems to work =

=3E nicely=2E=A0 =

=3E http=3A//www=2Edetailandstripes=2Ecom/3mwirorise08=2Ehtml=A0 It =

=3E sticks =

=3E things together very well=2C remains workable and is designed to =

=3E not squeeze =

=3E out from between the windshield and car frame or in our case the =

=3E base slab =

=3E and pressure container=2E
=3E =

=3E If a vertical has any long period sensitivity at all=2C it should =

=3E be pressure =

=3E sealed=2E
=3E =

=3E Good luck=2C
=3E Brett
=3E =

=3E Watch our wiggles
=3E http=3A//bnordgren=2Eorg/seismo/gif=5Fimages=2Ehtm
=3E =

=3E or watch some very very good wiggles
=3E http=3A//aslwww=2Ecr=2Eusgs=2Egov/Seismic=5FData/telemetry=5Fdata/AN=
MO=5F24hr=2Ehtml
=3E =

=3E =

=3E =5F=5F=5F=5F=5F=5F=5F=5F=5F=5F=5F=5F=5F=5F=5F=5F=5F=5F=5F=5F=5F=5F=5F=
=5F=5F=5F=5F=5F=5F=5F=5F=5F=5F=5F=5F=5F=5F=5F=5F=5F=5F=5F=5F=5F=5F=5F=5F=
=5F=5F=5F=5F=5F=5F=5F=5F=5F=5F=5F
=3E =

=3E Public Seismic Network Mailing List (PSN-L)
=3E =

=3E To leave this list email PSN-L-REQUEST=40SEISMICNET=2ECOM with =

=3E the body of the message (first line only)=3A unsubscribe
=3E See http=3A//www=2Eseismicnet=2Ecom/maillist=2Ehtml for more informa=
tion=2E
=3E 
Roger=2C=3Cbr=3EI am out of town right now=2E I thought you were in Monr=
oe LA =2E=2E=2ECould we talk by direct email=3F Mine is dickthomas01=40i=
nsightbb=2Ecom=2E I will get back late Monday=2E =3Cbr=3E=3Cbr=3E----- O=
riginal Message -----=3Cbr=3EFrom=3A Brett Nordgren =26lt=3Bbrett3nt=40b=
nordgren=2Eorg=26gt=3B=3Cbr=3EDate=3A Saturday=2C January 2=2C 2010 11=3A=
23=3Cbr=3ESubject=3A Re=3A Caution on=26nbsp=3B low pass filtering empha=
sis=3Cbr=3ETo=3A psn-l=40webtronics=2Ecom=3Cbr=3E=3Cbr=3E=26gt=3B Hi Rog=
er=2C=3Cbr=3E=26gt=3B =3Cbr=3E=26gt=3B At 09=3A37 PM 1/1/2010 -0800=2C y=
ou wrote=3A=3Cbr=3E=26gt=3B =26gt=3BHello Thomas=2C=3Cbr=3E=26gt=3B =26g=
t=3B=3Cbr=3E=26gt=3B =26gt=3BI took a look before and after the quake bu=
t did not see =3Cbr=3E=26gt=3B anything unusual=2E=3Cbr=3E=26gt=3B =26gt=
=3B=3Cbr=3E=26gt=3B =26gt=3BNot unusual for this location is to have a f=
uzzy trace (=7E1 Hz =3Cbr=3E=26gt=3B High Pass) =3Cbr=3E=26gt=3B =26gt=3B=
beginning about 0630 and ending about 1700 local times=2E=26nbsp=3B =3Cb=
r=3E=26gt=3B Since I am using =3Cbr=3E=26gt=3B =26gt=3Ba vertical=2C I h=
ave attributed this to the sun warming the =3Cbr=3E=26gt=3B =26gt=3Batmo=
sphere=2E=26nbsp=3B But=2C the noise does not seem to be present =3Cbr=3E=
=26gt=3B during non-work =3Cbr=3E=26gt=3B =26gt=3Bdays which is complete=
ly inconsistent with a solar source=2E=3Cbr=3E=26gt=3B =3Cbr=3E=26gt=3B =
Your description could almost be the definition for man-made=2C so =3Cbr=
=3E=26gt=3B called =3Cbr=3E=26gt=3B cultural noise=2E=26nbsp=3B Natural =
phenomena=2C though some might drop =3Cbr=3E=26gt=3B at night=2C aren=27=
t =3Cbr=3E=26gt=3B usually affected by weekends and holidays=2E=3Cbr=3E=26=
gt=3B =3Cbr=3E=26gt=3B =26gt=3B=26nbsp=3B I live about 2 miles from any =
serious auto traffic which =3Cbr=3E=26gt=3B would be on =3Cbr=3E=26gt=3B=
 =26gt=3B I-90 in Central Washington=2E=26nbsp=3B I have no explanation =
for =3Cbr=3E=26gt=3B this =22fuzz=22=3Cbr=3E=26gt=3B =3Cbr=3E=26gt=3B I =
think that you are almost certainly seeing truck traffic on =3Cbr=3E=26g=
t=3B the =3Cbr=3E=26gt=3B Interstate=2E=26nbsp=3B 2 miles is plenty clos=
e for a sensitive instrument=2E=3Cbr=3E=26gt=3B =3Cbr=3E=26gt=3B =26gt=3B=
The =22fuzz=22 is not visible with either the all pass or low pass =3Cbr=
=3E=26gt=3B filters in =3Cbr=3E=26gt=3B =26gt=3Bplace=2E=3Cbr=3E=26gt=3B=
 =26gt=3B=3Cbr=3E=26gt=3B =26gt=3BOne puzzle here is that in the past I =
could get a fairly clean =3Cbr=3E=26gt=3B FFT peak at =3Cbr=3E=26gt=3B =26=
gt=3Babout 6 seconds and little at longer periods=2E=26nbsp=3B Lately=2C=
 I =3Cbr=3E=26gt=3B notice a broader =3Cbr=3E=26gt=3B =26gt=3Bpeak at 6 =
seconds and a second peak as low as 44 seconds (both =3Cbr=3E=26gt=3B ve=
ry broad =3Cbr=3E=26gt=3B =26gt=3Bpeaks)=2E=26nbsp=3B I took a look at a=
bout 4 hours of data a few =3Cbr=3E=26gt=3B moments ago and =3Cbr=3E=26g=
t=3B =26gt=3Bconfirmed what I had previously found=2E=26nbsp=3B Would we=
 be seeing =3Cbr=3E=26gt=3B the same thing=3F=3Cbr=3E=26gt=3B =3Cbr=3E=26=
gt=3B The 6-second microseism peak is constantly changing=2C so =3Cbr=3E=
=26gt=3B changes=26nbsp=3B there are =3Cbr=3E=26gt=3B not that surprisin=
g=2E=3Cbr=3E=26gt=3B =3Cbr=3E=26gt=3B I agree that the low frequency pea=
k might very well be the =3Cbr=3E=26gt=3B atmospheric =3Cbr=3E=26gt=3B s=
tuff proposed by Chris=2C though verticals are mostly immune to =3Cbr=3E=
=26gt=3B the =3Cbr=3E=26gt=3B wind-caused ground tilting that is so anno=
ying with =3Cbr=3E=26gt=3B horizontals=2E=26nbsp=3B His =3Cbr=3E=26gt=3B=
 question about the pressure cover is a good one=2E=26nbsp=3B Normally =3C=
br=3E=26gt=3B the atmospheric =3Cbr=3E=26gt=3B noise we see on the verti=
cal is in the frequency range of =3Cbr=3E=26gt=3B minutes and is =3Cbr=3E=
=26gt=3B reduced by a factor of 10 or 20 by adding a sealed cover=2E=26n=
bsp=3B =3Cbr=3E=26gt=3B If your vertical =3Cbr=3E=26gt=3B is small enoug=
h to be covered by a cooking pot=2C that would work =3Cbr=3E=26gt=3B nic=
ely=2E=26nbsp=3B A =3Cbr=3E=26gt=3B typical setup would be a very solid =
base slab=2C like 2-4=22 thick =3Cbr=3E=26gt=3B granite=26nbsp=3B with a=
n inverted pot or similar container sealed =3Cbr=3E=26gt=3B down over =3C=
br=3E=26gt=3B it=2E=26nbsp=3B The granite base is because pressure chang=
es will =3Cbr=3E=26gt=3B cause anything much =3Cbr=3E=26gt=3B less solid=
 to flex under the seismo and generate noise=2E=26nbsp=3B =3Cbr=3E=26gt=3B=
 Our experience was =3Cbr=3E=26gt=3B that 3/4=22 aluminum flexes way too=
 much=2E=26nbsp=3B For sealing =3Cbr=3E=26gt=3B things=2C including =3Cb=
r=3E=26gt=3B cable openings=2C Dave Nelson has found that the putty-like=
 =3Cbr=3E=26gt=3B windshield =3Cbr=3E=26gt=3B sealant seems to work =3Cb=
r=3E=26gt=3B nicely=2E=26nbsp=3B =3Cbr=3E=26gt=3B http=3A//www=2Edetaila=
ndstripes=2Ecom/3mwirorise08=2Ehtml=26nbsp=3B It =3Cbr=3E=26gt=3B sticks=
 =3Cbr=3E=26gt=3B things together very well=2C remains workable and is d=
esigned to =3Cbr=3E=26gt=3B not squeeze =3Cbr=3E=26gt=3B out from betwee=
n the windshield and car frame or in our case the =3Cbr=3E=26gt=3B base =
slab =3Cbr=3E=26gt=3B and pressure container=2E=3Cbr=3E=26gt=3B =3Cbr=3E=
=26gt=3B If a vertical has any long period sensitivity at all=2C it shou=
ld =3Cbr=3E=26gt=3B be pressure =3Cbr=3E=26gt=3B sealed=2E=3Cbr=3E=26gt=3B=
 =3Cbr=3E=26gt=3B Good luck=2C=3Cbr=3E=26gt=3B Brett=3Cbr=3E=26gt=3B =3C=
br=3E=26gt=3B Watch our wiggles=3Cbr=3E=26gt=3B http=3A//bnordgren=2Eorg=
/seismo/gif=5Fimages=2Ehtm=3Cbr=3E=26gt=3B =3Cbr=3E=26gt=3B or watch som=
e very very good wiggles=3Cbr=3E=26gt=3B http=3A//aslwww=2Ecr=2Eusgs=2Eg=
ov/Seismic=5FData/telemetry=5Fdata/ANMO=5F24hr=2Ehtml=3Cbr=3E=26gt=3B =3C=
br=3E=26gt=3B =3Cbr=3E=26gt=3B =5F=5F=5F=5F=5F=5F=5F=5F=5F=5F=5F=5F=5F=5F=
=5F=5F=5F=5F=5F=5F=5F=5F=5F=5F=5F=5F=5F=5F=5F=5F=5F=5F=5F=5F=5F=5F=5F=5F=
=5F=5F=5F=5F=5F=5F=5F=5F=5F=5F=5F=5F=5F=5F=5F=5F=5F=5F=5F=5F=3Cbr=3E=26g=
t=3B =3Cbr=3E=26gt=3B Public Seismic Network Mailing List (PSN-L)=3Cbr=3E=
=26gt=3B =3Cbr=3E=26gt=3B To leave this list email PSN-L-REQUEST=40SEISM=
ICNET=2ECOM with =3Cbr=3E=26gt=3B the body of the message (first line on=
ly)=3A unsubscribe=3Cbr=3E=26gt=3B See http=3A//www=2Eseismicnet=2Ecom/m=
aillist=2Ehtml for more information=2E=3Cbr=3E=26gt=3B 

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