Which Geophones Are Specialized for Microseismic Monitoring?
Microseismic monitoring listens for tiny earthquakes triggered by industrial processes like hydraulic fracturing, CO2 injection, and mining. Unlike a regular seismic survey where you fire a controlled source and record the reflection, microseismic is entirely passive. You are waiting for events that may be magnitude -2 or smaller, generated when injected fluid changes pore pressure and causes slip on existing fractures.
Because the events are so small and the signal-to-noise ratio is poor, the sensor requirements are more demanding than for standard exploration work. You need geophones that can detect weak ground motion at a distance, capture the right frequency range, and record all three components to locate the event in 3D.
Three Things Your Geophone Needs for Microseismic
High Sensitivity
A standard 10 Hz exploration geophone at around 30 V/m/s works fine for active-source reflection. For microseismic, where your sensor may be hundreds of meters from a very small event, you want sensitivity above 80 V/m/s. High-sensitivity geophones achieve this through larger moving mass and higher coil impedance, producing more output voltage for the same ground motion.
Low Natural Frequency
Smaller earthquakes produce lower-frequency signals. A typical microseismic event has a corner frequency between 50 and 200 Hz. A 10 Hz geophone operating near its resonance will distort the waveform in exactly this band, making arrival-time picks unreliable. A 1 Hz or 4.5 Hz sensor keeps the resonance well below the signal you care about.
Three Components
You cannot locate an event in 3D with a single vertical component. You need P-wave and S-wave arrivals on multiple receivers, which means every station must record three orthogonal components. The vector data also drives the source mechanism, telling you whether the event was shear slip, tensile opening, or mixed mode.
Matching the Geophone to the Deployment
Where you put the sensor changes what kind of geophone you need:
Deep Borehole (500 m to 3,000 m)The best signal-to-noise ratio because you are close to the source. Deploy 8 to 40 triaxial sondes clamped to the borehole wall. Coupling is everything here: if the sonde is not rigidly locked to the formation, you introduce a resonance you cannot filter out in processing.
Shallow Borehole (30 m to 100 m)A cost-effective middle ground where you drill dedicated monitoring holes. Sensors sit below the weathered layer, reducing surface-wave noise. A 4.5 Hz 3C geophone cemented in casing works well for most projects.
Surface Nodal ArraysLarge grids of 1,000 to 10,000 autonomous nodes, each with a 5 Hz geophone, GPS, and battery. Lower signal-to-noise than borehole but the channel count gives you stacking power. Burial to half a meter is mandatory; a sensor sitting on the surface picks up wind and traffic noise.
Analog or Digital?
Analog moving-coil geophones still dominate large channel-count surveys because they are passive, cheap per channel, and compatible with existing recording systems. MEMS digital sensors give you flat response from DC to 800 Hz and automatic tilt calibration, which matters in borehole deployments where the sonde rotates. The trade-off is cost: a 10,000-channel MEMS grid costs far more than an equivalent analog grid, so most surface microseismic projects use analog sensors.
A Quick Frequency Guide
| Natural Frequency | Where It Is Used |
|---|---|
| 1 Hz | Deep microseismic arrays |
| 2 Hz | Deep microseismic arrays, regional monitoring |
| 4.5 Hz | Borehole and shallow-buried arrays, the workhorse frequency |
| 5 Hz | Surface nodal grids |
| 10 Hz | Surface arrays in noisy environments |
| 14 Hz | Not recommended for microseismic |
Coupling Matters More Than the Spec Sheet
A top-specification geophone produces useless data if it is not properly coupled to the ground. Poor coupling creates a spurious resonance in your waveform between 50 and 200 Hz, right in the band you are trying to record. It cannot be removed in processing because it is convolved with the real ground motion at the sensor.
For borehole: mechanical clamping with enough force is non-negotiable. For surface: bury the sensor, compact the soil, and avoid leaving it on the surface.
Summary
There is no one geophone for all microseismic projects. The right sensor depends on your deployment geometry, target event magnitude, background noise, and budget. Seis Tech supplies geophones across the 1 Hz to 100 Hz range, from geophone elements, land case geophones, and three-component geophones to complete borehole sondes with integrated locking mechanisms. For project-specific recommendations, contact our team with your deployment details.
Browse Geophones Suitable for Microseismic
High Sensitivity Geophone 2 Hz
High Sensitivity Geophone 4.5 Hz
Nodal Geophone 5 Hz
High Sensitivity Geophone 10 Hz
References
- Maxwell, S.C. 2014. Microseismic Imaging of Hydraulic Fracturing: Improved Engineering of Unconventional Shale Reservoirs. Society of Exploration Geophysicists.
- Warpinski, N.R. 2009. Microseismic monitoring: inside and out. Journal of Petroleum Technology, Volume 61, pages 80 to 85.
- Brune, J.N. 1970. Tectonic stress and the spectra of seismic shear waves from earthquakes. Journal of Geophysical Research, Volume 75, pages 4997 to 5009.
- Eisner, L., Hulsey, B.J., Duncan, P., Jurick, D., Werner, H. and Keller, W. 2010. Comparison of surface and borehole locations of induced microseismicity. Geophysical Prospecting, Volume 58, pages 809 to 820.
- Baig, A. and Urbancic, T. 2010. Microseismic moment tensors: a path to understanding frac growth. The Leading Edge, Volume 29, pages 320 to 324.
- Duncan, P.M. and Eisner, L. 2010. Reservoir characterization using surface microseismic monitoring. Geophysics, Volume 75, pages 75A139 to 75A146.
