Skip to comments.How Earthquakes in Chile Have Permanently Deformed Earth
Posted on 04/28/2013 11:43:29 PM PDT by LucyT
Earthquakes can permanently crack the Earth, an investigation of quakes that have rocked Chile over the past million years suggests.
Although earthquakes can wreak havoc on the planet's surface, more than a century of research has suggested the Earth actually mostly rebounds after quakes, with blocks of the world's crust elastically springing back, over the course of months to decades, to the way they initially were. Such rebounding was first seen after investigations of the devastating 1906 San Francisco temblor that helped lead to the destruction of more than 80 percent of the city. The rebound is well-documented nowadays by satellite-based GPS systems that monitor Earth's movements.
However, structural geologist Richard Allmendinger of Cornell University and his colleagues now find major earthquakes of magnitude 7 or greater apparently caused the crust in northern Chile to crack permanently.
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"It is only in a place like the Atacama Desert that these cracks can be observed in all other places, surface processes erase them within days or weeks of their formation, but in the Atacama, they are preserved for millions of years,"
Where I live near the the mouth of the Columbia River, the effects of subduction earthquakes can still be seen.
Along the road to Mt.Saint Helens, alongside roadcuts within the blast zone is evidence of past earthquakes millions of years old.
The Cascade Mountains and coast mountains here were formed from upthrusts caused by subduction quakes.
The volcanoes form upon the Cascades due to a huge, interconnected underground well of molten lava far beneath the surface resulting from when a plate is forced under the continental crust. When looking at the interior of the U.S., it is possible to see dead eroded volcanoes as evidence of continental formation.
You live in beautiful country.
OK everybody, you can now let loose the snarky remarks about hoping it blows.
This is so-o-o cool! I almost became a geologist 40-years ago. What a mistake I made by not doing so.
-——upthrusts caused by subduction quakes.-——
Or alternatively, as the subduction movement occurs, the dynamic force is transmitted upward through the rock and is felt as a quake.
Uh, I don’t know about that scenario.
Here in the northwest along the coast the subduction earthquake is out at sea where the marine plate is forced under the edge of the continental plate.
The coastline has been known historically (drowned forests along the coast) to cause the coastal areas to subside as much as 16 feet.
I'm no geologist, far from it..but the overwhelming majority of earthquakes of 7.0 or greater magnitude occur where the tectonic plates meet...IOW, where the earth is already cracked. Also, they're finding that most quakes NOT near a plate boundary are on fault lines that they didn't know existed before...and fault lines are just really smaller cracks.