Applied Geophysics : Seismics

Comparison of Seismographs

Applet ( in separate window, ca. 450 x 480 Pixel )

The applet compares
  amplitudes and phases of the transferfunctions with respect to ground displacement,
and
  the responses in the time domain to some impulsive ground displacements
  and
  some earthquakes, recorded at the station CLZ
  ( ground displacement restored from traces recorded with STS_2 )
for up to 3 of 12 historical instruments and actually used seismograph systems.

( Background : see Seismometer Documentaion
and Seismometer-Galvanometer Documentation,
see also Applet Response Functions of Seismographs,
in separate windows )

HowTo Screenshots Download

- HowTo -

Dialogue Window :
( Screenshot )

COMPARE SEISMOGRAPH SYSTEM : WIECHERT_Z...
alows to select up to 3 of the seismograph systems implemented :

> WIECHERT_H, WIECHERT_Z and WOOD-ANDERSON
>   are historical seismometers with "direct" recording,
>   characterized by natural period, damping and a static amplification ( = recorded amplitude / mass excursion ).

> WWSSN_SP / LP, BENIOFF_LP, GALITZIN, KIRNOS and DEMO_SP / LP
>   are seismometer - galvanometer systems, where
>   a velocity transducer ( coil-magnet-assemly ) of a seismometer is connected to the coil of a galvanometer via a resistive T element,
>   i.e. two resistances in series with seismometer / galvanometer coil and one shunt resistance.
>   ( see Seismometer-Galvanometer Documentation
>   and Applet Seismometer-Galvanometer Coupling )

> The geophones SM4_10Hz and L4_2Hz
>   are moving coil instruments connected to a digital recording system StrataView.

> The seismometer STS_2 ( Wielandt - Streckeisen )
>   is a force-balance broadband seismometer.
>   ( see Seismic Sensors and their Calibration, E. Wieland,
>   in New Manual of Observatory Practice.

> Details see Applet Response Functions of Seismographs.

SIG^2 = 0.980 ... 1.E-8
  refers to seismometer - galvanometer systems only, and
  allows to vary the value of the coefficient σ^2, preserving the other parameters of the system, to demonstate the influence of the coupling coefficient on the response curve.

  The default value of σ^2 ( from definition table ) is displayed on white background, user selected values on yellow background.
  ( Details of seismometer-galvanometer coupling see : Seismometer-Galvanometer Documentation )

SCALE x 1000 ... 0.001
  refers to the graphic display of earthquake recordings
  and allows to apply a scaling factor to the display of trace amplitudes.

F-SAMP ... ( = sampling frequency )
  refers to the Z-transform XFR ( Z ), used as a recursive filter to calculate the response in the time domain.

  It can be selected in the range 1 ... 800 [Hz], limited by the charakteristic frequencies of the seismograph system,
  or
  is determined by the sampling rate of the earthquake recordings to be displayed.

+LOWPASS
  includes a 4-pole Butterworth low pass ( corner freq. = F-SAMP7nbsp;/ 8 ) in the recursive filtering to reduce aliasing errors.

CLEAR TEXT ...
  clears the text area of the applet
  and lists
  the parameters of the actually selected system ( LIST SEIS ),
  the coefficients of the frequency response and / or of the corresponding Z-transform ( LIST COEFF ),
  and
  the frequency / time response ( FREQ / TIME RESP ).
  ( TIME RESP lists max. 500 samples starting from t = 0 [s], CONT TIME lists subsequent blocks of 500 SMP each. )

INFO and HELP
  display informations to the actual cursor position ( INFO )
and / or
  hints to actually possible mouse actions ( HELP )
in the graphic display windows.

The graphic display is controlled by the display dialogue ( background light blue ) :

> XFR ( F ) / XFR ( Z ) / F + Z
> shows the frequency response and/or the corresponding Z-transform
> ( AMPL = ampltude, PHAS = phase in separate windows )
> for the seismograph systems selected.

> HIDE RESP WIN ...
> hides / shows the output signals in the time domain for different ground motions :
>   DELTA IMP ( = Dirac impulse ),
>   UNIT STEP,
>   KUEPPERS_2 ( = Kueppers signal, order 2 ),
>   or
>   K_2 x HANNING ( = as above, with Hanning taper ),
> or
>   one of the four earthquake recordings implemented.

> ( 200 SMP...10 SMP refers to Kueppers signals only and allows to select the signal length and, together with F-SAMP, the predominant frequency of the signal,
> SCL x 1.0...x 100 refers to the graphic display of the ground displacement of the earthquake examples. )

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- Screenshots -

Seismographs : WOOD-AND., WWSSN_LP and KIRNOS,
response to ground displacement
( param. see below : screenshot Text Area )

Colors : magenta = WOOD-AND., cyan = WWSSN_LP, blue = KIRNOS.

- Frequency Domain -

XFR ( F )
Amplitude ( AMPL ) and phase ( PHAS ) of frequency response

Positioning the mouse cursor on the label FCT ( blue, upper left corner ) shows informations to the curves displayed ( type, scaling and color code, etc. ).

XFR ( Z )
Amplitude ( AMP ) of Z-Transform
( F-SAMP 80 [Hz], +LOWPASS )

- Time Domain -

Resp. to UNIT STEP
( XFR ( Z ) as above, red = input signal = ground displacement )

Earthquake recording HALLE
( F-SAMP 80 [Hz], +LOWPASS, red = ground displacement )

Earthquake recording TURKEY
( F-SAMP 20 [Hz], +LOWPASS, red = ground displacement )

For earthquake recordings F.S. ( full scale ) refers to the amplitude range between the reference lines ( marked 0 ) of the neighbouring traces and corresponds to a trace excursion of
  ±0.2 [m] on a recorder for all "direct" recording and seismometer-galvanometer seismographs,
  ±10 [V] of output voltage for the geophones SM4 and L4,
  and
  ±20 [V] for the seismometer STS_2.

For the ground displacement of an earthquake, the F.S. value [μm] for SCL x 1.0 is chosen to cover the amplitude maximum.

- Text Area -

LIST SEIS :

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- Download -

Class and html files for a local installation of the applet are available as a zip file and as a tar.gz file.

More applets at : Geophysics Department TU Clausthal

Rev. 12-nov-2012

Comments to Fritz Keller
( ned gschempfd isch globd gnueg )

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