EARTHQUAKE and CONTINENTAL DRIFT

EARTHQUAKE UPDATE

Yesterday's earthquake will not receive recognition in comparison to great earthquakes of the past, or even the present severe one in Nepal this past week.  One five years ago in Haiti resulted in the death of over 316,000 people; the second largest (in fatalities), recorded after 800,000+ in 1556 in China, was followed by 300,000 in 1737 in Calcutta, India.

The geologically stable (relatively) state of Michigan had its worst earthquake in 1947, not far away, near Coldwater at 4.6 on the Richter scale, whereas the 4.2 or 4.4 of yesterday ranked second and was centered about five miles south of Galesburg, in Kalamazoo County near Scotts and Climax.  For comparison the Haiti quake was 7.0 but the even larger quake of 2011 rated at 9.0 caused the death of over 20,000 due the large tsunami generated as a result of its offshore location in close proximity to Fukushimi, Japan.

THE CAUSE OF YESTERDAY'S QUAKE

Because it was centered over three miles deep, those quoted on TV and/or in the paper thought it was not related to the much shallower depth of wells involved in possible fracking activities there.  It is along a fault line running from NW to SE through the area and many miles in each of those directions.

So it was thought to be due to two of the earth's crustal plates shifting or sliding over one another.  It started me thinking about continental drift, plate tectonics, and their causes and effects.  I mentioned glacial rebound (I should have said crustal rebound from the demise of the continental glaciers).  Such rebound it evident from the high past shorelines of Lakes Michigan-Huron noted on Mackinac Island compared to other locations.

CONTINENTAL DRIFT

The movements of continents and the formation of the Atlantic Ocean are well accepted now.  When I arrived in Tasmania in 1956, a international conference on Continental Drift had just been completed.  They were telling me it was well accepted as a concept by all but the American geologists who thought there was no cause known to be strong enough to cause the movement.  I had already thought the biogeographic evidence was so strong it had to be true.  So I mused about how the earth was a little bit similar to a simmering pot of soup.  The upwelling generated by the heat below produced a column that rose and spread carrying surface material aside.

Once the earth's surface cooled sufficiently and the crust was thick and lighter the accumulation may have caused a reversal of the circulation due its insulating effect and an new column arose under it to disperse the present continents and widen the Atlantic.  The collisions following such movements and continued pressure produced by oceanic plates caused some of the subsequent mountain building and other events.  The reduction of deep sources of heat due to decay of radioactive elements may have caused some decline in rates of crustal movement.

DOES THE MOON HAVE A ROLE?

When I looked at the paper and saw we will have a full moon tonight, I thought about the role of tides in the above movements.  Could it have been the straw that broke the camel's back; were tides of sea and earth reaching a peak that triggered quakes.  Probably not, but perhaps tides could be a factor in minor crustal movements that accumulate to cause quakes etc.

The tides move a tremendous amount of water and its attendant weight about with approximately a twice daily cycle that is of greater magnitude during a twice monthly cycle when sun, moon, and earth or sun, earth and moon are aligned.  When the stresses produced by tides are aligned with crustal movement forces, the movements could show a twice daily cycle of speed or movement if measurements were able to record them.  Then again, it may just be my imagination.

MICHIGAN'S GLACIAL GEOLOGY

I thought about Michigan geology.  The Lower Peninsula of Michigan has subsurface geology resembling a stack of saucers.  Devonian deposits outcrop around the rim and progressively younger deposits are at the surface as you go to the central part.  Above the Devonian are layers that include salt, gypsum, coal, limestone, and sandstone of varying thickness.  Bedrock is topped by glacial till containing predominately sand, gravel, and clay in an unconsolidated layer as much as 1,000 feet deep in some places.  In many places the water of the melting glaciers left nearly horizontal layers varying according to the materials the melting glacier carried and the flow of the departing water.

Since the coral deposits and other marine material indicated it formed in a shallow sea, it occurred to me that perhaps the saucer like shape of the layers was due to glacial weight after the shallow sea sediments had been deposited.  A likely candidate was late Permian glaciation near the end of the Paleozoic Era that was associated with the extinction of about 95% of marine and terrestrial species.  It was long before the Atlantic Ocean became a significant body of water.  Once the continental glacier, centered on or north of Michigan, got high enough, the altitude effect would prevent melting and perhaps produce a massive ice mountain deforming the flat sediments to its cup shape configuration.

When continental glaciation more recently happened (during Pleistocene glaciation), it is thought to have been centered farther north in Canada so the scouring effect increased the depth of the Great Lakes and caused the formation of the Finger Lakes in New York State.


Joseph G. Engemann    May 3, 2015