A Lippmann style seismometer (Lippmann and Gebrande, 1983) uses a
single-coil velocity-feedback method in order to extend toward lower
frequencies a geophone's frequency response. Strong seismic signals may
saturate the electronics, sometimes clipping the signal or producing the
characteristic whale-shaped recording.
Adding a non linear feedback in the electronic circuit may avoid saturation,
allowing the strong-motion use of the seismometer without affecting the
usual performance. Such a seismometer will allow unsaturated data in
epicentral area while offering nice low signal recording for far events. |