Sensors at IRIS/IDA sites

IDA uses a suite of sensors to capture the full range of geophysical information in the environment surrounding an IRIS GSN site. The sensors may be grouped into several broad categories:

  • primary seismometers:  For many years either the STS1 very broadband seismometer manufactured by G. Streckeisen AG or a KS54000-IRIS manufactured by Geotech Instruments, LLC was employed to record accurately very long period to mid-frequency-range seismic data.  If a tunnel or suitable subsurface vault is available, the STS1 was deployed.  If not, a 100m-deep borehole is drilled and a KS54000-IRIS was used. Since 2017, the GSN has been updating the primary borehole sensors in the network.  KS54000 units whose performance has degraded or have failed entirely are being replaced with either the Streckeisen STS-6A or the Nanometrics Trillium 360-BH seismometers. The STS1 vault/tunnel deployed sensors are being replaced with Nanometrics Trillium 360SV-GSN vault seismometers.
  • secondary seismometers:  Because the STS1 and the KS54000-IRIS do not record the higher frequency portion of the seismic spectrum with the fidelity desired by the IRIS community, an auxiliary sensor is installed at nearly all sites.  The auxiliary sensor may be one of several models:  the STS-2STS2.5, or the STS-5A made by G. Streckeisen AG and the Trillium 240 or Trillium 120PH made by Nanometrics,Inc. Two secondary sensors used originally in the GSN, the CMG-3T made by Guralp Systems Ltd, the GS-13 made by Geotech Instruments, LLC, have been phased out.
  • strong motion accelerometers:  The above seismometers will behave in a non-linear fashion when subjected to high accelerations. In order to record acceleration up to 2g with fidelity, a strong motion instrument is installed at most sites. The strong motion instrument in use at IRIS/IDA stations is the EpiSensor FBA ES-T made by Kinemetrics, Inc.
  • microbarographs:  Because of the effect of air pressure on long period seismic recordings and because geophysical phenomena such as volcanic eruptions generate pressure waves of interest, microbarographs are also installed at GSN stations. The models used at IRIS/IDA stations are the 6016B made by Paroscientific, Inc. and the Setraceram Model 270 made by Setra.