[SAC-HELP] Instrument responce files

[Sheila Peacock]

Dear Shekar,

Guralp seismometers (CMG-40T) all have different response
files.  If you know the serial number of your seismometer,
email it in the subject line to caldoc at guralp.com
and you will get a data sheet for it by return email.
Beware, though, that the poles and zeros listed therein
are in velocity in Hz, not displacement in radians.
You have to multiply them by 2pi and put in an additional
zero at (0.0,0.0) to get them into displacement units in
a form that SAC expects.

You will then have to calculate the "constant" (or normalising
factor) using the revised poles-and-zeros, rather than using the
value on the Guralp sheet.

Some Guralp seismometers have poles and zeros listed in
acceleration units - check the units in which the
"velocity output" is given on the first page of the
calibration sheet.  If so then you have to add TWO
zeros at (0.0,0.0).  I think a GMG-40T calibration is likely to
be in velocity units, though.

Sheila Peacock,
Blacknest.


PS does anyone on the list know of a good self-contained
program for calculating the constant (normalising factor)
of a set of poles and zeros?  Or even a good website that
describes how it's done?  Encapsulating the explanation
into an email without recourse to mathematical symbols
is something of a challenge.