## PSN-L Email List Message

Subject: Relative Mag Calc question
From: Stephen & Kathy skmort@............
Date: Sun, 25 Mar 2007 15:42:25 -0700

```Calc. Problem #1
On my AS-1, it shows a P to P count of 147.48 with a period of 3.6
seconds for the P wave of the 7.2 Vanuatu quake on 3 March 07!  I divide
by 3.6 to get a one second count of approx. 41.

Later, another event from Vanuatu gives me a count of 90.58 at 4.5
seconds,, which converts to a count of about 20.

Assuming that the converted one second counts are proportional to ground
motion, and that the second event produced about half,  I found the log
of .5 = about -.3,,   summed to 7.2 = approx. 6.9 for an approx. mag for
the second event!!  distance and depth are about the same, is the
distance to great for this kind of relative calculation?

I'm about 6080 miles from the two events!

Calc. Problem #2
Using the USGS quake distance calculator I find that my estimated one
second ground motion for the 7.2 Vanuatu quake would be 1.4 micro meters!

On my AS-1,  225 counts = one volt!   Can I assume 41 / 1.4 = approx 29
count per micro meter per second = .13 volts per micro meter per second
sensitivity?????   (or convert to proper terminology????) and or does
2pi enter in somewhere???   I see the 2pi factor in the USGS calculator
from micro meter to micro meter per sec?  (.13 * 2pi = .82 v / micro
meter / s)

Any tutoring on my overly simple process, and or assumptions are welcome!!!
Please make it as simple as possible, thanks.
Stephen
PSN Station #55
38.828N  120.979W

Calc. Problem #1
On my AS-1, it shows a P to P count of 147.48 with a period of 3.6
seconds for the P wave of the 7.2 Vanuatu quake on 3 March 07!  I
divide by 3.6 to get a one second count of approx. 41.

Later, another event from Vanuatu gives me a count of 90.58 at 4.5
seconds,, which converts to a count of about 20.

Assuming that the converted one second counts are proportional to
ground motion, and that the second event produced about half,  I found
the log of .5 = about -.3,,   summed to 7.2 = approx. 6.9 for an
approx. mag for the second event!!  distance and depth are about the
same, is the distance to great for this kind of relative calculation?

I'm about 6080 miles from the two events!

Calc. Problem #2
Using the USGS quake distance
calculator I find
that my estimated one second ground motion for the 7.2 Vanuatu quake
would be 1.4 micro meters!

On my AS-1,  225 counts = one volt!   Can I assume 41 / 1.4 = approx 29
count per micro meter per second = .13 volts per micro meter per second
sensitivity?????   (or convert to proper terminology????) and or does
2pi enter in somewhere???   I see the 2pi factor in the USGS calculator
from micro meter to micro meter per sec?  (.13 * 2pi = .82 v / micro
meter / s)

Any tutoring on my overly simple process, and or assumptions are
welcome!!!
Please make it as simple as possible, thanks.
Stephen
PSN Station #55
38.828N  120.979W

```