[SAC-HELP] Wiechert seismometer instrumental response

[George Helffrich]

Dear Maria Carmen Pro -

	Wiechert instruments had very large masses, giving them effectively a displacement response: i.e. instrument output is proportional to ground displacement.  The response built into SAC has:

Zeros: 2 at (0.,0.)
Poles: 2 at (-omega0*h, omega0*omega), (-omega0*h, -omega0*omega)

where omega0 = 2*pi/9.65, h = 0.403712752, and omega = sqrt(1-h**2).

Response source:  AMPLITUDE AND PHASE RESPONSES ARE COMPUTED FROM EQNS. (82), (98), AND (13) OF SOHON (1932), SEISMOMETRY, IN PART II OF INTRODUCTION TO THEORETICAL SEISMOLOGY, J. B. MACELWANE AND F. W. SOHON, JOHN WILEY AND SONS, NEW YORK.

	For a displacement response, the two zeros are puzzling.  However, that is what SAC has and I cannot offer any enlightenment as to why or whether it is truly correct.  An historical seismologist might be better equipped to explain.

On 1 Jun 2015, at 15:51, Maria Carmen Pro Munoz <cpro at unex.es> wrote:

> 
> Hi,
> 
> I'd like to know the instrument type for the Wiechert seismometer in SAC when yo use "trans to WIECH", I mean, if it is a velocity or displacement instrumental response and poles and zeros values.
> 
> Best,
> 
> Carmen Pro
> 
> -- 
> _________________________________________
> Carmen Pro Muñoz
> Dpto. Física- Universidad de Extremadura
> Centro Universitario de Mérida
> c/ Sta. Teresa de Jornet, nº 38
> 06800 Mérida (Badajoz)
> Tfo. 924 289300- ext:82544
> _________________________________________
> 
> -- 
> _________________________________________
> Carmen Pro Muñoz
> Dpto. Física- Universidad de Extremadura
> Centro Universitario de Mérida
> c/ Sta. Teresa de Jornet, nº 38
> 06800 Mérida (Badajoz)
> Tfo. 924 289300- ext:82544
> _________________________________________
> 
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          George Helffrich
          george.helffrich at bris.ac.uk