## PSN-L Email List Message

Subject: Short period vs Long period
From: tchannel1@............
Date: Wed, 5 Mar 2008 15:07:53 -0700

```Hi All,   Perhaps someone can explain the different in recorded data, =
between a (let's say a Lehman) at 2 second period and the same sensor at =
20 seconds.

I have compared data from two such sensors.   Here is what I have found, =
but I am sure I am understanding the TRUE difference.

I get smaller EQ's on the shorter periods,  my guess is about 1/3 more =
events.   Mainly on the closer EQ's or smaller EQ's for the 2 second =
machine.

That is not to say the 20 second period machine, does not pick these up, =
just not as many, if they are weak.  =20

If it is a big event I get it on both machines equally?   If it is a =
medium event I get it on both machines.  But, if it is weak, definitely =
better on the 2 second machine.=20

About the only difference, I can see on the 20 second machine traces is =
the duration.   On a 8.0M the 20 second trace could be three hours long =
on the 2 second machine maybe only one hour.

I do understand the teleseismic, traveling greater distances, loses the =
higher frequencies, and those remaining can be in the range of 10-20 =
seconds.
However I pick up the teleseismic very well on the 2 second machine, =
they are  just not as long in duration.

Hi All,   Perhaps someone can =
explain the=20
different in recorded data, between a (let's say a Lehman) at 2 second =
period=20
and the same sensor at 20 seconds.

I have compared data from two such=20
sensors.   Here is what I have found, but I am sure I am =
understanding=20
the TRUE difference.

I get smaller EQ's on the shorter =
periods,  my=20
guess is about 1/3 more events.   Mainly on the closer EQ's or =
smaller=20
EQ's for the 2 second machine.

That is not to say the 20 second period =
machine,=20
does not pick these up, just not as many, if they are weak.  =20

If it is a big event I get it on both =
machines=20
equally?   If it is a medium event I get it on both =
machines. =20
But, if it is weak, definitely better on the 2 second machine. =

About the only difference, I can =
see on the 20=20
second machine traces is the duration.   On a 8.0M the 20 =
second trace=20
could be three hours long on the 2 second machine maybe only one=20
hour.

I do understand the teleseismic, =
traveling greater=20
distances, loses the higher frequencies, and those remaining can be =
in the=20
range of 10-20 seconds.
However I pick up the teleseismic very =
well on the=20
2 second machine, they are  just not as long in =
duration.

Thanks, Ted
```