GEOPHONE FAQ



What is a geophone?

Who makes/sells them?

How much are they?

What does it have to do with ghost hunting?

What's the difference between all of the different models?

What do they look like?

Who uses them?

How do they work?

Is a geophone the same thing as an accelerometer or seismometer?

What are spurious frequencies?

How old are geophones? When was the first one made?

Mine says "Pollard" on it or looks like a stethoscope on one end.

What types of information can you get out of a geophone?

What makes me an expert on geophones?


I had a link to email me and the spam harvesters got ahold of it. So now there's no way to send corrections, additions, etc... Sorry.


What is a geophone?
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...

Who makes/sells them?
Here are a few links to companies that either make, lease or sell geophones:
GeoSpace
Mitcham Industries
Geotool
GISCOGEO
R. T. Clark
Sercel(Mark Products)
Ion Geophysical

How much are they?
It depends on a lot of different factors. Basically the price is between free to beyond $1000.00 U.S.. I have two used 10 Hz geophone kits that I bought for about $10.00 U.S. each. The more complicated, lower resonant frequency, multiple channel, name brand, new geophones cost more money. The older, simpler, single channel, used geophones are cheaper. I don't sell geophones.

What does it have to do with ghost hunting?
Ghosthunters is now using a geophone or possibly an accelorometer to detect vibrations so they can be recorded by the camera. Their geophone is only acting as a detector. They don't digitize the signals to be analyzed or interpreted, except with the camera. Normally the amplified signal from a geophone would be digitized and recorded or just recorded to paper with a chart recorder. The kit they use on Ghosthunter looks like something you might find at BG Micro, eBay or maybe United Nuclear. I would guess the value at around $30 USD, if you're shopping for something similar.

What's the difference between all of the different models?
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 light weight and a low price. Basically you want the resonant frequency to be close to what your 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.

What do they look like?
They look like little metal cylinders mostly. They vary in size and proportions with different connectors and some go into little cases. There are some pictures on the web sites listed elsewhere on this page.



Geosource MD-81 10 Hz geophones next to ruler for scale.

Who uses them?
Oil companies, security companies, mining companies and seismologists both amateur and professional.

How do they work?
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 velocity of motion. The current is used to move a pen over paper or gets recorded into a computer for analysis.

Is a geophone the same thing as an accelerometer or seismometer?
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 intended axis.

What are spurious frequencies?
This information was given to me and I tried to paraphrase it for simplicity. 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. Some values I saw while poking around are pretty high and would not effect seismic signals. At least not distant seismic events.

How old are geophones? When was the first one made?
Real seismometers go back to the 1900's. Geophones probably came shortly after.

Mine says "Pollard" on it or looks like a stethoscope on one end.
It's not a typical geophone with a coil and a magnet. It's for listening for underground leaks in pipes.
Here's a good link.

What types of information can you get out of a geophone?

What makes me an expert on geophones?
Actually, I'm an amateur and I have a passing interest in seismology. Please, do not base your thesis on things I've written.


last updated 01-28-2013