The Streckeisen STS-1 is a leaf-spring seismometer which employs a force-feedback system to extend the bandwidth and linearity of the seismometer. The Berkeley Seismological Laboratory has STS-1 seismometers installed at several sites.
This photograph illustrates the installation of the 3-component STS-1 seismometer at BKS. The instruments sit on base plates, coupled to the pier via a layer of sand. The bell jars provide thermal stability and protect the seismometer from hostile environmental conditions. The bell jar is evacuated on the vertical component, in order to reduce the noise introduced by atmospheric variations (which change the buoyancy of the seismometer's mass), but are not evacuated on the horizontal components. After installation is complete, the seismometers are covered with 4" of polyurethane foam for additional thermal insulation.
For more information on the installation and operation of the BDSN, please see the guidelines for installing broadband seismic instrumentation.
Wielandt, E., and G. Streckeisen, The leaf spring seismometer: design and performance, Bull. Seis. Soc. Am., 72, Part A, 2349-2367, 1982.
Wielandt, E., and J. Steim, A digital very broadband seismograph, Ann. Geophys., 4b, 227, 1986.