Moment Magnitude Scale for 2012 Giant Earthquake – The Big One

In the new science of earthquake measurement theory, we have two important terms to differentiate: seismic moment and magnitude scale. These variables replace the old concept of the Richter scale.

Seismic moment is a quantity that combines the area of the rupture and the amount of fault offset with a measure of the strength of the rocks – the shear modulus m.

The equation relationship between their variables is represented as:

Seismic Moment = m x (Rupture Area) x (Fault Offset)

Usually we measure the moment directly from seismograms devices, since the size of the very long-period waves generated by an earthquake is proportional to the seismic moment. The physical units of seismic moment are (force) x (distance), with the result expressed in dyne-cm.

For scientific studies, the moment is the measure we use since it has fewer limitations than the magnitudes, which often reach a maximum value that we call magnitude saturation.

To compare seismic moment with magnitude, Mw, we use a formula constructed by Hiroo Kanamori of the California Institute of Seismology and Tom Hanks of US Geological Survey (Journal of Geophysical Research, Vol. 84, No. B5, May 10, 1979), which follows the relationship:

Mw = 2 / 3 * log (Seismic Moment) – 10.73

where the units of the moment, Mo, are also expressed in dyne-cm, in a logarithmic scale of base 10.

The symbols used to represent the different magnitudes are:

Magnitude Symbol Wave Period
Local (Richter) ML S or Surface Wave* 0.8 s
Body-Wave mb P 1 s
Surface-Wave Ms Rayleigh 20 s
Moment Mw Rupture Area, Slip > 100 s

*at the distances appropriate for local magnitude, either the S-wave or the surface waves generally produce the largest vibrations.

The seismic moment and moment magnitude give us the tool we need to compare the size of the largest quakes. We find that the “moment release” in shallow earthquakes throughout the entire century is dominated by several large subduction zone earthquake sequences. First, let’s compare the amount of energy released in the different plate settings:

Earthquake Moment 1900-1989

Based on the above figure, Lord Pakal Ahau has given us a surprising diagram with his prophetic vision for the major 2012 California earthquake called The Big One. It follows the science of prediction but also the 2012 Prophecy of the Virgin of Guadalupe explained here in the same year when the Venus Transit happens explained here.

We can just compare the largest earthquakes (those with magnitudes greater than 9) with all the other shallow earthquakes and the expected California earthquake in 2012 in the old Juan de Fuca subduction plate. It is our mathematical Maya prophecy in action!

Giant Earthquakes 1900-2012

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