PSN-L Message - Subject: Re: Period of seismic units

To: psnlist@.............. Sent: Fri, October 15, 2010 10:32:41 AM Subject: Period of seismic units I asked Larry about this and he wanted me to post it here. I think he = was trying to get rid of me. It probably shows how little I know and = that I am missing something. This question came out of the activity in = the Guy area which is about 500 miles west of me as well as the New = Madrid system which is closer. It seems the records are better on the = 2-4 Hz units. Here was my question; > It is about this geophone vs lehman or other long period = instruments. In > California you have many local quakes. These quakes have frequencies > higher than long distance quakes. What is the logic of (just/or = popularity of) long > period instruments out there? What precipitated this trend? The 1-5 = Hz units should be better on local events -- which you have a lot. There are many California quakes and there is the activity in = Washington State and Yellowstone but you never see local seismic = detectors being posted with periods of 1-4.5 Hz -- except possibly = tchannel. Shouldn't these units help differentiate human noises like = quarry activity from smaller local earthquake activity? __________________________________________________________ Public Seismic Network Mailing List (PSNLIST) To leave this list email PSNLIST-REQUEST@.............. with the body = of the message (first line only): unsubscribe See http://www.seismicnet.com/maillist.html for more information.

Hi Len, I can only answer for = myself, and for=20 my area of the country.

I usually operate three sensors, One = Lehman NS, one=20 Lehman EW, both 20 seconds, and a vertical 1.5 seconds.

On my homebuilt equipment, I find very = good results=20 with the 1.5 vertical, for local, and near regional events. = It also=20 will make a nice recording from anywhere in the world of = >6.8. =20 Really nice >7m

However, the down side is it will only = record the=20 P,S and a portion of the longer frequencies. A typical = recording of=20 a 7M from Asia, may only last 20 mins.

Now the Lehmans.......They miss many = small events,=20 that the vertical picks up............They never miss the mid size, = nor the=20 large events, and on the typical recording of a 7M, may record four = hours,=20 compare to the vertical 20 mins.

So I love having both, at lease one = vertical, and=20 one Lehman. I am sure others, with different equipment = would=20 see different results.

Many times, I look at my sensors to = find only one=20 of the two types recorded anything of value. I would not = like to be=20 without my vertical. Limited as it is.

My posting may not reflect this, as I = very=20 often, get too busy to post all three. I am trying to = operate=20 five or six at a time, and may only post one of interest.

Cheers, Ted

----- Original Message -----

From:=20 Len=20 Polucci

To: psnlist@.............. =

Sent: Friday, October 15, 2010 = 2:51=20 PM

Subject: Re: Period of seismic=20 units

Great, Great question! Since I have no idea and have wondered in = the=20 past..I'd love to see some answers!

From: Thomas Dick = <dickthomas01@.............= >
To: psnlist@..............
<= SPAN=20 style=3D"FONT-WEIGHT: bold">Sent: Fri, October 15, 2010 = 10:32:41=20 AM
Subject: Period = of seismic=20 units

I asked Larry about this and he wanted me to post = it here.=20 I think he was trying to get rid of me. It probably shows how little I = know=20 and that I am missing something. This question came out of the = activity in the=20 Guy area which is about 500 miles west of me as well as the New Madrid = system=20 which is closer. It seems the records are better on the 2-4 Hz units. = Here was=20 my question;

> It is about this geophone vs lehman or other = long=20 period instruments. In
> California you have many local quakes. = These=20 quakes have frequencies
> higher than long distance quakes. What = is the=20 logic of (just/or popularity of) long
> period instruments out = there?=20 What precipitated this trend? The 1-5 Hz units should be better on = local=20 events -- which you have a lot.
There are many California quakes = and there=20 is the activity in Washington State and Yellowstone but you never see = local=20 seismic detectors being posted with periods of 1-4.5 Hz -- except = possibly=20 tchannel. Shouldn't these units help differentiate human noises = like=20 quarry activity from smaller local earthquake=20 = activity?

________________________________________________________= __

Public=20 Seismic Network Mailing List (PSNLIST)

To leave this list email = PSNLIST-REQUEST@SEISMIC= NET.COM=20 with the body of the message (first line only): unsubscribe
See=20 http://www.seismicnet.com/maillist.html for more=20 information.

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