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Basic Information of Geophone

06 May.,2024

Basic Information of Geophone

I. Q: When was the first geophone made?

If you want to learn more, please visit our website What Is Geophone.

A: Real seismometers go back to the 1900s. Geophones probably came shortly after.

II. Q: What is the basic information of geophone

A: A geophone is a small, cheap instrument for measuring ground motion. There are many different varieties for different applications. They are designed for earthquakes, machine vibrations, oil exploration, mining, etc.

III. Q: Who uses the geophone?

A: Oil companies, security companies, mining companies and seismologists, etc.

IV. Q: How do geophones work?

A: Most of the models have a coil hanging from a spring in the center of some magnets. When the case is moved up and down the mass tends to stay put and induces small currents into the coil as it moves through the magnetic field. It measures the velocity of motion.

V. Q: Is a geophone the same thing as an accelerometer or seismometer?

A: Not really. Geophones would sit in between accelerometers and seismometers in function and price.

Seismometers are typically larger and more expensive. They usually detect extremely small movements at lower frequencies than geophones. Seismometers can be very fragile and sensitive, although they are designed to survive earthquakes, that may be from hundreds of miles away. Calibrating a seismometer might be critical to getting useful data out of it and a geophone or accelerometer would more likely to be used just to get a simpler signal.

Accelerometers are nearly solid state and good at handling more violent motion. Video games and cell phones are now using accelerometers to interact with the users as another input device.

All three might have a intended axis or orientation (XYZ or Mercator plus vertical) or they might be a bundle of more than one axis in the same package. Single-axis instruments are limited in function off of the intended axis.

VI. Q: What’s the difference between all of the different models of geophones?

A: There are huge differences between the models and options for geophones. The exterior case is optional on a lot of geophones. Some have coaxial connectors and some have binding post connectors, but most have two little pins that you connect your leads to. The resonant frequency is one of the main factors in the price. Lower resonant frequencies are more difficult to achieve in a small box with a lightweight and low price. Basically, you want the resonant frequency to be close to what you’re looking for in signals.

Also, your application should be a factor. You probably don’t need a 1 Hz resonant frequency to watch local earthquakes, but you would want one for distant earthquakes. The frequency response of an instrument is probably centered around the resonant frequency and is very narrow in width.

VII. Q: What are spurious frequencies of geophone?

A: Basically, it’s the noise from high-frequency oscillations in the suspension spring. The spring inside the geophone that supports the mass, can pick up higher frequencies and add noise to the signal.

VIII. Q: What is the typical technical specifications of a seismic geophone ?

A:– Natural Frequency– Coil Resistance
– Moving Mass
– Harmonic Distortion
– Open Circuit Damping
– Damping With Shunt Resistor
– Sensitivity With Shunt Resistor
– Open Circuit Intrinsic Voltage Sensitivity
– Damping Calibration-shunt Resistance
– Typical Case To Coil Motion p-p
– Typical Spurious Frequency, etc.

What do I need to know about geophones?

Geophones are used in seismic investigations to transform the vibration in the ground to a voltage. The geophones are analogue instruments, with a spring-mounted wire coil moving past a magnet. This creates the electrical signal which is recorded by a seismograph such as the Terraloc.

Further on, it is also good to have a hint on the following.

Different geophones

There are three types of common geophones: vertical, horizontal and multi-component. And these can have different frequencies. Typically, we use vertical geophones for refraction and surface wave studies and horizontal geophones for reflection and multi-component for some advanced studies of the ground motion. Also see 3C and Omnidirectional below. Note that for survey in water we can use sensors that detect pressure changes rather than vibrations and these are called Hydrophones.

Geophone frequencies

The choice of geophone frequency will depend upon the type of seismic investigation being undertaken and the application. Surface wave methods must use low frequency geophones below 5 Hz, while refraction typically uses 10-28 Hz geophones and reflection surveys will normally use 10-40 Hz geophones. High frequency ratings on the geophone give greater resolution but limit the depth/distance that the seismic energy will be detected at.

Frequency rating of a geophone

Geophones have a “resonant frequency” – this is the frequency of vibration at which they prefer to oscillate and therefore give the biggest response. Low frequency geophones are good at detecting low frequency vibrations and these are the one which travel deep and far. A higher frequency geophone will respond best to faster oscillations which are the ones which create more detail. For ground vibrations at frequencies either side of the resonance rating, a geophone will record those above the rating better than those below so, if in doubt, it is better to use a geophone with too low frequency than too high.

For more Smartsolo Nodal Seismic Acquisition Systeminformation, please contact us. We will provide professional answers.

Horizontal geophones for reflection surveys

Although reflection surveys can be undertaken with vertical geophones, for near-surface survey we recommend horizontal units because:

They minimize the effects of refracted waves.
Random noise tends to be dominated by P-wave motion.
Shear wave velocities can help differentiate between similar V
P
velocities.
They will be measuring shear movement and S-waves travel slower, equating to shorter wavelengths and thus better resolution.

Using the same geophone for refraction, reflection, and surface wave methods

Under specific circumstances you can use the same geophone for all three different types of investigations, but your data would be compromised.

The 4.5 Hz vertical geophones used in surface wave studies could be used to collect refraction and reflection data, but the resolution would be reduced. This will be a bigger problem for reflection investigations where the aim of the survey may be to map stratigraphy in detail.

And compromising on use of a single geophone will not work the other way round: in other words, higher frequency geophones – suited to good quality refraction and/or reflection work – will not be appropriate for surface wave surveys, as these require frequencies below 5 Hz.

3-component (3C) geophone

Regular geophones have a single sensor in them which is orientated to be sensitive to either horizontal motion or vertical motion. A 3-component geophone has three sensors inside – one mounted vertically and two mounted horizontally at 90° to each other (to measure ‘left-right’ and ‘forward-backward’ horizontal motion). These are commonly used for HVSR (Horizontal-to-Vertical Spectral Ratio) surface wave studies and monitoring projects.

Omnidirectional geophone

An omnidirectional geophone is a single geophone sensor which will operate equally well regardless of its orientation (right way up, sideways, upside down, at an angle).

Basic Information of Geophone