Gravimetry

Gravimetry and Gravity gradiometry is a field of science which supposedly measures the strength of the earth's gravitational field. In these discussions Gravimetry is often used as evidence that the gravitational field of the earth varies with latitude and by location.

It has been found that Gravimetry is not directly measuring gravity at all. Gravimeter devices have been described by professionals in that field as long-period seismometers that are measuring small "jerks" in the background seismic noise and interpreting it as variations in gravity. Gravimeters are, in truth, seismometers. Seismometer devices have been described as having a "gravimeter mode." Seismometers can double-purpose as gravimeters, and can detect the "gravity tides". Gravimeters are often similarly double-purposed as seismometers to detect earthquakes thousands of miles away. Perhaps most illustrative, gravitational anomalies on gravity maps are indistinguishable from the seismic zones. Finally, there are several items which do not make sense with the gravity anomalies, if they were actually a measurement of mass.

The theory behind the field of Gravimetry is that the masses in the subsurface are creating tiny variations or jerks, presumed to be due to "gravity", that are measured by the devices in a unit of measurement called uGal or mGal. We read a description of Gravity Gradiometry on Wikipedia:

https://en.wikipedia.org/wiki/Gravity_gradiometry (Archive)

=What is Gravimetry?=

A quote from the Enhanced Geothermal Innovative Network for Europe (Archive) explains:

From Gravity surveying: a brief introduction (Archive) we read:

In The Gravity Method (Archive), its author Dr. Nicolas O. Mariita tells us:

The Global CCS Institute (Archive) says:

=Seismometers are Gravimeters=

Comparitive Study
Comparative study of superconducting gravimeters and broadband seismometers STS-1/Z in seismic and subseismic frequency bands (Archive)

Diagram from p. 212:



The paper says that when comparing with Gravimeters to the Seismometers, the gravity spectra is nearly identical:

Tidal Detection
Further, the above paper states that seismometers are also able to detect the tides -- p.204, second paragraph:

It is mentioned that the "gravity tides" are found in the subseismic band:

A definition of "subseismic band" (Archive):

Is a study of subseismic activity a study of gravity?

Gravimeter Mode
From https://en.wikipedia.org/wiki/Gravimeter (Archive) we read:

The reader might ask, if gravimeters are entirely different devices than seismometers, how could seismometers have a "gravimeter mode"?

=Gravimeters are Seismometers=

This inventor describes gravimeters as follows:

http://www.njsas.org/projects/tidal_forces/magnetic_gravimeter/baker/ (Archive)

From p.2 of a paper on seafloor measurements (Archive) from the Journal of Geophysical Research we see:

On p.4 of The Gravity Method (Archive) by Dr. Nicolas O. Mariita we read another reference:

Again, we see that the gravimeter is actually a seismometer, and will be easily disrupted by seismic activity and other noise.

Recall from the above seismometer section that the seismometer was detecting gravity tides on subseismic bands, which was described as:

Hence, the gravimeter is a low-frequency seismometer, like the seismometer above, taking data out of those low-frequency bands.

Function of a Gravimeter
It is often argued that a gravimeter works by dropping a body and measuring the full acceleration. While some types of gravimeters drop bodies, others do not. Consider how the following gravimeter works:

https://schmidtocean.org/rv-falkor/operations-and-science-systems/gravimeter/ (Archive)

With the above device there is not a falling object. The magnetism suspends the cylinder. The system then measures changes to that cylinder.

As directly stated, the interest isn't in the total pull. The designers mainly care about using the device as a seismometer.

Absolute Gravimeter Description
From Geophysics From Terrestrial Time‐Variable Gravity Measurements we read about a device that does involve a falling object. The interest is in the tiny noises that affect the mirror in the device:

Monitoring earthquakes with gravity meters
From the abstract of a paper titled Monitoring earthquakes with gravity meters (Archive) we read:

The ending two sentences of that abstract even imply that gravity meters may be superior for measuring seismic elements.

Earthquake Comparison Readings
From the study we see several seismic reading comparisons between gravimeters and seismometers:





Gravity anomalies observed before earthquakes
Pre-seismic gravity anomalies before Linkou Ms 6.4 earthquake by continuous gravity observation of Crustal Movement Observation Network of China (Archive)

The reader may ponder why the gravity of the earth would change before an earthquake.

=Corrections for Latitude=

It is asserted that gravimetry has shown trends at different latitudes, and so this is validation of the idea that it is really measuring "gravity". We find that this assertion is unfounded.

From a university course on gravity surveying we read:

http://www.geol-amu.org/notes/m10-1-4.htm (Archive)

If the objective of gravity surveys is merely to look for deviations from a round earth reference model with the vibrating gravity theory, then the final computed number in meters per second squared would becomes meaningless for the purpose of discussion. Any modifications to the reference values are constructed on an entirely theoretical basis.

The above page tells us that there is a theoretical model and that the goal of gravity surveys is to modify that model. Further down we see, among the list of corrections to be made, the latitude correction:

We read that we are subtracting or adding values to the reference model and the data to make the corrections for latitude, which is very different than using the data to determine the latitude. The claim that the final number is meaningful as evidence to showcase any particular point is shown fallacious.

United Nations University
On p.9 of Seismic Activity, Gravity, and Magnetic Measurements (Archive) by LaGeo as part of the United Nations University Geothermal Training Program we read:

The section goes on to list a number of corrections, including corrections for latitude and elevation, which is not data contained in the measurement readings:

=Seismic Map Similarities=

Convergent Plate and Earthquake Map
Compare the gravity anomalies to a map of the plate boundaries and the earthquake zones:



Seismic Hazard Maps






=Perplexing Anomalies=

The anomalous deviations of gravity, as detected by the gravmieter, are called Bouguer Anomalies.

https://en.wikipedia.org/wiki/Bouguer_anomaly explains:

Note that a correction for latitude needs to be made, and that the data is not in the gravimeter readings itself.

Gravity Anomalies Counter To Theory
"Bouguer Anomalies Over The Continents and Oceans" in the Journal of the Geological Society of India tells us that the anomalies are often greater over the ocean than over the land, which is contrary to gravity theory:

The anomalies are negative in continental areas and positive in oceanic areas. The anomalies are also negative in the mountains. These anomalies appear to go against the theory that the anomalies are due to the attraction of mass.

Bouguer Anomalies - Australia
We find the following depiction of Australia's Bouguer Anomalies and Free Air Anomalies on a University of California Berkeley lecture on gravimetry (Archive) (p.3), showing that the anomalies are negative over continental areas and positive over oceanic areas:



Bouguer Anomalies - Alps of Germany
https://www.leibniz-liag.de/en/research/methods/gravimetry-magnetics/bouguer-anomalies.html

The above map and description shows that the anomalies are negative in the Alps of Germany.

=Seismic Wave Propagation=

Background Seismic Noise
It should be noted that there is constant background seismic noise, which emanate from the earth. From http://microglacoste.com/gPhoneNoise/gPhoneSeismicNoise.pdf we read:

Airborne Seismic Waves
It should also be noted that seismic waves can become airborne, which would explain the ability of gravimeter devices on airplanes to register the anomalies.

https://en.wikipedia.org/wiki/Seismic_wave