Seismometer Sensitivity: Unit, Richter-Scale, Magnitude

• mersecske
In summary, a seismic sensor has a sensitivity which is related to the velocity of the sensor. The order of magnitude of the seismic background is not known.
mersecske
What is the unit of sensitivity of a seismometer?
What is V/(m/sec)?
How can we compare this value to the Richter-scale?
What is the order of magnitude of the seismic background?

mersecske said:

What is V/(m/sec)?

that's is Volts / metres / sec that is the "Velocity" type of sensor (magnet and coil arrangement

In the USA you will often see V/in/sec Volts /inch/sec... an example of a commercial geophone with a 4.5Hz resonant freq has a sensitivity of 0.810V/in/sec

for recording strong local events that would max out a velocity sensor ( unless sensitivity was turned way down) Accelerometers are used and the output from them is recorded as a percentage of g (gravity). so depending on the strength of the event you mite get a recording of 0.4g or maybe 1.2g etc etc. ground type, distance from event and other factors affect that measurement

it has no relationship to the Richter scale.

the Richter scale is a function of the measurement of the largest 0 (zero) line to peak movement of the ink pen on the seismogram and then using a nonogram when the distance is registered the magnitude is worked out (see image below). Richter developed the scale to deal with earthquakes in the local ~ 100km maximum distance, from the seismometer and for a specific type of seismometer. The term Richter scale has been severely misused by the media for many many years !
There are other more accurate ways used these days for evaluating the magnitude of an earthquake. The main one is the Moment magnitude which better represents the amount of energy released by the quake.

cheers
Dave

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seismology is a passion of mine, having run my own seismic station from home since the early 1990's for the first few years it was just a ink pen/rotating drum recorder in the mid '90's I added a digital recorder.
There's a large number of us around the world doing amateur seismology.
the 2 pix below show
1... a close up of the drum with a large recorded event
2... the drum recorder and in the background the digital system

cheers
Dave

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What is the order of magnitude of the seismic background?

not sure what you mean by that question
do you mean... what is the background noise level ? that depends on where the seismometer is located, some locations are noisier than others with man-made seismic noise

my seismic system would pick up cold fronts approaching from as far out as 12 hrs. On my trace ( I lived within 5km of the ocean) I could see the heavier seas pounding on the coastline long before the front actually arrived.

Dave

1. What is the unit of measurement for seismometer sensitivity?

The unit of measurement for seismometer sensitivity is nanometers per second (nm/s). This unit indicates the displacement of the ground caused by seismic waves.

2. How is the Richter scale used to measure earthquake magnitude?

The Richter scale is a logarithmic scale used to measure the magnitude of an earthquake based on the amplitude of the seismic waves recorded by a seismometer. Each whole number on the scale represents a ten-fold increase in amplitude, with higher numbers indicating a larger earthquake.

3. What is the difference between magnitude and intensity in relation to earthquakes?

Magnitude is a measure of the size or strength of an earthquake, while intensity refers to the effects or damage caused by the earthquake at a specific location. Magnitude is a quantitative measurement, while intensity is a qualitative assessment.

4. Can a seismometer measure earthquakes of all magnitudes?

Yes, a seismometer can measure earthquakes of all magnitudes. However, smaller earthquakes may not be detectable by seismometers located far from the epicenter, making it more difficult to accurately measure their magnitude.

5. How is seismometer sensitivity calibrated?

Seismometer sensitivity is calibrated by using a known ground motion, such as a controlled explosion, and measuring the resulting output of the seismometer. This allows for adjustments to be made to the instrument's settings to ensure accurate measurements of seismic activity.

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