Take a look at this chart. What we have is a clear thirty year rise inearthquake activity starting around 1960 and then dropping of for adecade. The last decade it has returnedto the secular uptrend and has now made up for any lost ground. Thus we have a clear fifty years of stableactivity counts with no apparent trend, followed by fifty years of double theactivity and a secular uptrend.
This may well be the result ofchanging data collection capability, although I find that to be a bit of astretch. The seismograph sees throughthe earth and the first handful did the trick quite well. I think we can now accept a higher level ofseismic activity that continues to be sustained and equally unexplained. Most certainly it shows little correlation tosunspot activity or other non earth source.
It is better to bite the bulletand accept that this is a natural earth cycle and we need to understand it. The apparent length of the cycle itself is prettyeasy to understand as it can be mapped against a model based on the ring offire in which certain significant events over time translate into furtherevents along the boundary.
Thus a cycle in activity, whichmay be century’s long or even millennia long, is implied by the very existenceof the ring itself which is slowly shrinking around the Pacific Plate. That there should be internal cycles couldsimply reflect the random selection of triggers that allow a spat of them totake place and may actually be a residual echo of a major event many millennia ago.
I bring that up because thePleistocene nonconformity is exactly one such event that would still drive sucha wave of seismicity even today.
In fact knowledge of such longcycle seismicity may even be the underlying argument for certain ancient predictionsthat crop up in arguments for 2012 and the like.
Right now the take home is thatsuch a cycle appears to exist and begs consideration and watching. Do notforget that the San Andreas is way overdue.
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