The Greatest Recorded Earthquake

PROLOGUE

I was born in Santiago, but my earliest memories date from the years my family spent in Iquique, in the far north of Chile. There, I first attended school. There, I made my first friend, Carlitos. There was created my most vivid early memory….

Our house faced a convent.  Normally, high convent walls concealed nuns of a cloistered order. But in Chile earthquakes are a part of life. And what one does in an earthquake of any magnitude is rush out into the middle of the street…. And so my family did early one morning when our house began to rattle and shake, along with everyone else who lived on that street, including the nuns.  O, the shock to my infant eyes, at the emergence of these secreted sisters!  Not only were the tabernacled beings at last revealed, but out of habit!  In identical white nightdress!  Exposing nothing ordinarily not exposed by non-nuns, but … heads bare, when nuns’ heads never were! AND …  shaved? Or maybe, hair just cropped short … for sudden marvel can lead to loss of detail in the most vivid of young memories….

My point here that in Chile geology is not just looked at and walked upon, it happens to you, shocks you … and ultimately shapes you.  You live with the catastrophic volcanic eruptions that now and then happen, here and there, but even more with earthquake—past, present and pending—for they never really stop. You can expect their shock at any moment. You can be dining and see the lamp over the table begin to tremble … a non-event, unless it escalates….

NazcaPlate

And this is true along almost all of Chile’s amazing length, for the geology of the country is created by the clash of two tectonic plates, the Nazca subducting under the South American (as depicted at the right). This creeping titanic collision is what created the Andes in the first place, and continues to reshape them. This subduction also created Chile’s volcanoes, and generates its earthquakes.

Below is a depiction of Chile’s earthquakes as circles, diameter indicating severity, color indicating depth.  One notes that earthquakes stop where the Nazca plate ends, so that the extreme south of Chile is relatively free of temblors.  One also notes that earthquake depth is proportional to the distance from the subduction line, which is off the coast.  This makes sense, for the Nazca plate grinds its way down at an angle.

Earthquakes in Chile

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MAY 22, 1960

On this date, the greatest earthquake to be recorded occurred in southern Chile, its epicenter 570 kilometers south of Santiago–the city most affected being Valdivia.  The magnitude was 9.5–the largest since estimations of magnitude became possible in the twentieth century.

global-seismic-moment-release

But the impressive numeral does less justice to this event than the chart to the right, for the seismic energy released summed to 20 percent of all the earthquakes of the 20th century!  (Note the renowned San Francisco earthquake’s share, as the paltriest of wedges.) The release of energy is estimated to have been198 gigatons–the equal of 1000 atom bombs….chile earthquake

There were several foreshocks of magnitude 7 or more (full fledged quakes in themselves), which did considerable damage but, by giving warning–fortunately reduced mortality from collapsing structures.

By far the most damage and loss of life was caused by the tsunami subsequent to the main quake.  The fault displacement occurred about 100 miles offshore, paralleling the coast along a line 560 to 620 miles long, causing a tsunami approximately 80 feet high (24 meters) which struck land along that length.  Below, a photograph of the aftermath at Corral, a harbor near Valdivia….
tsunami:chileBelow is an image of a different location, taken from the air.   Structures not annihilated were slammed by the tidal wave into far locations….
tsunami-damage-chile-sm  But Chile was not the only place affected.Tsunami travel time  The tsunami propagated across the Pacific (as illustrated to the left, with elapsed time and wave intensity depicted). Traveling at over 200 miles per hour (a speed to astonish not just Captain Cook!) the tsunami caused major damage and high mortality at distant locations.  It struck the island of Hawaii (about 6700 miles distant) with a wall of water 35 feet high, bending parking meters to the ground, and destroying Hilo Harbor.

Hilo tsunamiTsunami damage, Honshu, JapanRacing on, Waves 18 ft high slammed into Honshu, Japan,15 hours after the quake (about 10,700 miles away!) destroying 1600 homes and leaving 160 dead or missing.

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PREHISTORY

Apocalyptic destruction such as this–so far exceeding ordinary human scale–is difficult for even the twentieth century to ‘comprehend’ ( etymologically to wrap our arms–or less etymologically, our minds–around).  Now, imagine just such an earthquake and consequent tsunami before there was measurement or history, in the land now called Chile….

The Mapuche (“people of the land” in their language), are the indigenous inhabitants of this violently tectonic place, and in their version of their origin they have a huge serpent, Kaikaifiilu, inundate their land, their ancestors being those who survived by fleeing into the mountains….

No need of an Old Testament God in Chile, for in that land geology is Genesis.