October 12, 2012 – Time to “Eat Some Crow:” My recent post stated that global earthquakes are not increasing; referencing a USGS analysis. Tonight I completed an analysis of 5,415 global earthquakes, from 1973 to 2011 – that were greater than or equal to (>=) 6.0 magnitude.
The quantity of earthquakes by year is shown above. The yellow horizontal line is a two year linear projection line. At least over the last 40 years, the quantity of quakes is increasing.
Below is the same graph, only summing the magnitude of those 5,415 quakes:
It would appear that the magnitude of those quakes is also increasing.
Below is a graph of the 10X power rating of those quakes:
Here is the USGS explanation of earthquake strength (10X versus 32X Ratings): “The magnitude scale is really comparing amplitudes of waves on a seismogram, not the STRENGTH (energy) of the quakes. So, a magnitude 8.7 is 794 times bigger than a 5.8 quake as measured on seismograms (10X Rating Graph above), but the 8.7 quake is about 23,000 times STRONGER than the 5.8! Since it is really the energy or strength that knocks down buildings, this is really the more important comparison (32X Rating Graph below). This means that it would take about 23,000 quakes of magnitude 5.8 to equal the energy released by one magnitude 8.7 event.
The 32X Rating of the same 5,415 earthquakes is shown below. Note the peaks in 2004, for the Sumatra mega-quake and tsunami that killed over 228,000 (Dec. 26, 2004), and 2011, for the Japanese mega-quake and tsunami (March 11, 2011). The strength of really large earthquakes is clearly shown in the graph below:
This explains why big quakes are so much more devastating than small ones. The amplitude (“size”) differences are big enough, but the energy (“strength”) differences are huge. The amplitude numbers are neater and a little easier to explain, which is why those are used more often in publications. But it’s the energy that does the damage.
Unfortunately, all four of these graphs have a linear trend lines sloping up, for the future. A powerful earthquake that struck near the surface, in a heavily populated area such as Tokyo or Los Angeles, would be unimaginably destructive and costly.
The Master of Disaster