As seismologists gained more experience from earthquake records, it became obvious that the problem could not be reduced to a single peak acceleration. In fact, a full frequency of vibrations occurs.
By moving them vertically, a representative mean curve could be formed, and individual events were then characterized by individual logarithmic differences from the standard curve.
Emphasis was usually put on the horizontal acceleration factor, for the simple reason that ordinary structures have a built-in safety factor for the vertical component; that is, gravity.
For example, some stars put out large amounts of energy in the infrared part of the spectrum, so that this can produce a different relative magnitude rating than using light energy from the middle of the spectrum.
From here, it becomes an engineering problem; the engineer considers the ground motion that will occur and evaluates the requirements of the proposed structure in the light of the local foundation conditions.
I repeatedly have to correct this belief. In a sense, magnitude involves steps of 10 because every increase of one magnitude represents a tenfold amplification of the ground motion. But there is no 'scale of 10' in the sense of an upper limit.
I suggested that we might compare earthquakes in terms of the measured amplitudes recorded at these stations, with an appropriate correction for distance.
I usually point out that most loss of life and property has been due to the collapse of antiquated and unsafe structures, mostly of brick and other masonry.
If the assumptions used in calculating energy are changed, then this seriously affects the final result, even though the same body of data might be used.
In every area of the world where there is earthquake risk, there are still many buildings of this type; it is very frustrating to try to get rid of them.
Incidentally, the usual designation of the magnitude scale to my name does less than justice to the great part that Dr. Gutenberg played in extending the scale to apply to earthquakes in all parts of the world.
Intensity like signal strength will generally fall off with distance from the source, although it also depends on the local conditions and the pathway from the source to the point.
There is another common misapprehension that the magnitude scale is itself some kind of instrument or apparatus. Visitors will frequently ask to 'see the scale.'
