Changing the Magnitude of an Earthquake: Why downgrade/upgrade?

Why do seismologists change the magnitude of an earthquake?
Obtaining an accurate preliminary magnitude can be difficult due not only to the complex processes that occur deep within the Earth, but because there are over a dozen techniques of for calculating the magnitude of an earthquake. In this animation we look at two magnitude scales, and use two examples of magnitude changing.

Animation and graphics by Jenda Johnson, geologist, Earth Sciences Animated
Narrated by: Dr. Wendy Bohon, Informal Education Specialist, IRIS
Written by Jenda Johnson and Dr. Wendy Bohon,
Reviewed by: Dr. Anne Trehu, seismologist, Oregon State University and Dr. Danielle Sumy, Project Associate, IRIS
ShakeMap intensity maps from the United States Geological Survey
NEIC earthquakes animation from Pacific Tsunami Warning Center (NOAA)
“Blind Thrust” fault model by Brad Aagaard
Photographs from the United States Geological Survey
“Global Resonance” by Knights of Fire (Burnt Promises album)
Maps from Google Earth

[BenFerraiuolo]

I understand this explanation completely. Its just weird how the majority of the time reported earthquakes are downgraded, instead of upgraded. Why is this?

[tamarackmi]

Thank you...I have been watching earthquakes with a youtuber Dutchsinse for nearly the last 11 years....I have wondered why we get different magnitude reports.

[nevrabulut]

magnitude changing is also depend on the epicenter distance to the recorders. for example, Mw value of any EQ can be calculated differently at closer recorder and at farthermost recorder.

[zamazalotta]

How about reporting magnitudes with their estimated errors, so people can know how much of a correction to expect?

[rexremedy]

If the Richter scale is not suitable above mg5, why would you you publish measurements based on Richter principle, which are thus faulty above mg5 anyways? Why not just wait until the moment scale data comes in? Why not defunct any Richter measurement above mg generally?

[suzannehartmann]

So how many OTHER official government agencies change the magnitude of earthquakes after reporting them? MUCH of the stored data is available to anyone who requests it but it obviously limited and NOT available to EVERYone who requests it. Sometime data is available at certain times and not others from the same station as observed bay a NUMBER of youtube posters who simply make the data available to subscribers with or without comment as to why. Getting a preliminary magnitude has nothing to do with complex processes deep in the earth because it is simply based on measurements. INTERPRETING it is based upon assumptions about processes happening deep in the earth. So initially there are measurements. Then a collection of these measurements are crunched and analyzed and interpreted. Determining the actual hypocenter is an interpretation so all calculations based upon it are subjective. The video makes it sound like settled science. The problem is the variables. One example is the slide at 3:53. The variables listed are Amplitude (measured) (Distance:calculated) Area (also calculated) and Rigidity( virtually unknown). Why do I say that rigidity is unknown? All of the rock in the calculated area would have to be reasonably sampled to the depth indicated to establish the rigidity and that has simply not happened on a sufficient scale. The sampling is far between and shallow. It has happened where and when there has been a reason for someone to drill for oil or water or some other reason not in a scientific or specific pattern. And certainly not to a uniform depth throughout earthquake prone regions. As I pointed out area and distance are both calculated and are based on the presumed (calculated) hypocenter. That is too many variables to reasonably call this scientific therefore many peopee do not find these calculation to be based on enough measurements and known data to be credible. Thus the label magic. I am a scientist with twenty years experience in medical labs and if I had worked this way we would have killed people not healed them.

[wildearth]

Hum it’s normal USGS downgrade hardly ?
If Japanese Agence said that the earthquake is 6.0 in Osaka it’s true.
Not a 5.3