BOREHOLE SEISMOMETERS: WHAT MATTERS?

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The first key consideration for a seismometer is the frequency response. Typically, a lower frequency response is better for natural seismicity / larger earthquakes, while higher frequency responses are required for induced seismicity / microearthquakes. The majority of the sondes that we manufacture are gimballed 2Hz and 4.5 Hz triaxial instruments, but we also make gimballed 1 Hz and fixed 15 Hz instruments.

Sonde Reliability is the next key consideration. In extreme conditions, it is important to reduce or remove potential failure mechanisms as far as possible. So, it is better to have geophones (which are self-powered) rather than accelerometers which are externally powered. Similarly, any gimballing (for levelling the sensors) is better done mechanically rather than electronically.

Temperature & Pressure: Most geophones are rated range from 60 to 150ºC, but you will also need to consider the temperature rating of the sonde, cable and any accessories.

Accessories include hydraulic hole-locks, key locks, magnetometers, and other sensors (temperature, pressure etc.)

Because your sonde is in a borehole, your datalogger is probably going to be a long way from the sensors, so a very low noise datalogger is needed. We use Reftek dataloggers because they have been proven to be low noise.

IESE manufactures a range of borehole seismometers for extreme applications. The forerunner of today’s design was installed in 1985 at Parkfield, where 11 of the 12 sondes are still working. To date over 400 sondes using the basic IESE design have been installed worldwide.

Applications include

  • geothermal,
  • scientific observatories,
  • regional national networks,
  • reservoir monitoring,
  • varied energy technologies,
  • EGS,
  • CO2 sequestration,

We are leaders in the design of instruments for the harshest conditions including:

  • hot (150ºC; experimental test up to 195ºC),
  • deep (3.3 Km), and
  • 60º borehole deviation (for specific gimbaled unit only)
Posted in Technical