Download Along this axis of the Aleutian Trench lies the subduction zone, in

Along this axis of the Aleutian Trench lies the subduction zone, in which the marine crust of
one plate is “diving” or being steadily pushed beneath the lip of the continental crust of
another plate. This diving at an angle sends cool surface rock deep below, and where the
temperatures rise sufficiently due to geothermal energy, former marine crust melts to
become magma. A line of volcanoes, several hundred km inland of the trench or subduction
zone represents the locations along which this magma tends to make its way to the surface,
in the form of volcanoes.
Before the 1964 Alaska Earthquake, this picture of subduction was hotly debated, and some
of its advocates treated to scales of ridicule such as greeted erstwhile heretics, Alfred
Wegener and J Harlen Bretz. A revolution in thinking swept geologists temporarily
camping out in Alaska, because they were desperately needed here to contribute data. I like
to think of it as the “Coleman Stove Revolution” in honor of the way in which geologists
camped, chatted with people they never would have met otherwise, and had their eyes and
minds opened to a new, synthetic way of thinking.
For millions of years, this subduction has been adding to the continental crust around
Alaska, hence to the North American Plate, by a process of skimming the less dense, less
massive surface layers from these colliding and diving plates at the edge of marine crustal
plates. Here, the process is likened to scooping up material with a front end loader.
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Fortunately, several years before Wegener died in Greenland, a Dutch geophysicist, Felix Vening
Meinesz contrived to test the theory that very deep oceanic trenches represented mysterious forces at
the edges or boundaries of continental plates. If there were unseen forces tugging or forcing
sedimentary rock downward toward the center of the Earth at the bottoms of these trenches, sensitive
measurements of the acceleration due to gravity should be measurable as especially weak
gravitational fields. Vening Meinesz perfected twin pendulums swinging in opposite directions to be
the analog measurement tools for detecting gravity anomalies. Next he needed a stable platform
from which to make his measurements on specially designed gimbals. In the stormy seas above the
Java Trench, surface ships would be too bouncy for accurate measurements, so Vening Meinesz hit
upon the idea of mounting his instruments in submarines of the day (1923-27).
A wonderful image emerged in my mind when I read about this inconveniently large Dutchman from
Delft supervising sailors’ making measurements with gravimeters in a couple of cramped pre-WWII
submarines belonging to the Dutch Navy. Having solved each of the other 3 problems, Vening
Meinesz enjoyed one of these important “Eureka” moments of 20th century western sciences.
As soon as word got out to other scientists, Harry Hess, Teddy Bullard, and Maurice Ewing, they
could not wait to get Vening Meinesz to come over to the Caribbean, and to verify his gravimetric
trench findings over deep Caribbean trenches. Wegener lived long enough to be aware that the first
stirrings of interest in continental drift theory were focusing attention on geological processes in the
deepest of the planet’s ocean recesses. The intrepid Dutchman had led the way to vindicating
Wegener: continental plates do have edges, and they are moving!
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One final side-trip: Mythology holds that Alfred Wegener died un-appreciated, and
completely un-vindicated in 1930. There’s a delightful story writ in gravity studies of the
ocean floor that tells us that this myth is not fully accurate. In the early 1920s, an intrepid
Dutch geophysicist, Felix Vening Meinesz, argued that if continents do in reality drift, then
they must collide with one another at their edges at various places around the globe. Just
possibly, he thought, some of these contacting edges can be found on the seafloor, more
easily than on land. His attention was drawn to particularly deep oceanic trenches. If these
were places where continental plates collided, he reasoned, extra rock mass might
accumulate, and that temporary excess mass should be detectable with instruments capable
of measuring the acceleration due to gravity near these trenches.
Four problems had to be overcome. 1. sensitivity of gravimetric instruments; 2. The
instability of ships as platforms for gravimetry; 3. The physics explaining any excursions
(positive or negative anomalies) from background acceleration due to gravity; 4. This
Dutchman’s own positive excursion from normal body mass!
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1.
Research and synthesis attempts during the 20th century brought about associations of
people and ideas in patterns that only make sense in hindsight.
1. U.S. resistance to Continental Drift was based on methodological, conceptual, and
philosophical preferences among U.S. earth scientists;
2. Big names in 20th century earth science tended to be European, familiar with American
investigations, but to have learned even more from European war-related endeavors during
WW II;
3. U.S. institutions, nevertheless played pivotal roles in theoretical developments that took
place at an accelerating rate, notably at Cambridge, Princeton, Lamont, and Scripps.
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As soon as I read that Felix Vening Meinesz was an uncommonly large man, who exceeded
body height and circumference limits for normal submariners, (especially under Admiral
Rickover, father of the U.S. Nuclear Submarine Fleet) the devil in me made me look for
images of Vening Meinesz on the Internet. Sure enough! Can you pick him out? And the
two submarines pictured here traveled from the Netherlands through the Panama Canal, to
the Dutch East Indies and back to carry out these gravimeter surveys of the Java Trench.
With Vening Meinesz aboard the whole time!
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John Nance’s 1988 book, On Shaky Ground, attempted to raise public concern for the illpreparedness of the U.S. to deal with catastrophic earthquakes. Essentially, half the book
treats the 1964 earthquake in Alaska to illustrate how far the various geological sciences had
advanced in interpreting the dynamics of Earth processes in the 20th century. These
scientific advances are the good news. The bad news is how poorly the advances are
translated into adjustments in public policy toward earthquake and volcano hazards.
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In Cascadia’s Fault by Jerry Thompson (2011) I discovered that the Alaska
Earthquake of 1964 has NOT been totally forgotten, nor is it fading from the
consciousness of serious writers and chroniclers of science. Peterson considers
one of the smaller pieces of oceanic crust in the Ring of Fire, the Juan de Fuca
Plate, the semi-attached Gorda Plate, and the Cascadia Subduction Zone,
shown here. Despite its small size, the Juan de Fuca Plate is subducting under
the North American Plate between the San Andreas Fault and northern British
Columbia. It WILL rupture and rearrange its temporary connection with the
NAP, and there will be major—great—earthquakes between northern
California and the northern end of Vancouver Island. What happened beneath
the Queen Charlotte Islands on 28-29 October 2012? A false alarm or foretaste
of Cascadia’s release of seismic energy?
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This is the best account for lay readers since John Nance’s 1988 book, and is
substantially updated.
Once again, the Alaska Earthquake of 1964 comes in either first or second
among earthquakes used as learning tools. The main contender is the 2011
Japan Tohoku-Oki quake. I’ve also noted that a couple of the heroic geologists
featured in Nance’s book, Brian Atwater, and George Plafker, a leader among
1964 Alaska Earthquake field studies, are well discussed, as judged by the
number of mentions of each in the book’s Index.
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Alaska’s 1964 Earthquake produced long-distance tsunamis detected all around the Pacific
Rim.
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Tsunamis, nevertheless, did not get the attention they probably deserved for quite a few
years. Then came the 2004 Boxing Day Sumatra Earthquake and tsunami with huge loss of
life in places like Banda Ache. And more recently, on 11th March 2011, Japan was hugely
devastated by the earthquake and tsunami known as Tohoku Oki. Since then, its name has
gravitated toward that of the afflicted nuclear power plant known as Fukushima.
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Still, people away from low-lying coastal regions tend not to grasp the immense danger
from the destructiveness of tsunamis and local coseismic submarine landslides. In more
populous and lower-latitude regions of the world, people tend to inhabit coastal zones. The
British seismic hazards writer, Musson has written of the certainty that there will be an
earthquake someday that will claim a million lives in a subduction zone event somewhere
around the Pacific Rim. Could be a Cascadia event. Or a Sumatran event, or ?
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Minami-Sanriku was the hardest hit coastal community in Japan in 2011, both in destruction
and loss of life. The coastal zone was largely flattened by the tsunami, with just a few tall
buildings serving as refuges from high water. Back from the immediate coastline, the high
water swept all the way to the couple of foreland and heights where a larger number of
people fled than made it to upper floors of tall buildings.
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