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Why do EQs occur a long way from Plate boundaries?

16 May 2024

At https://www.livescience.com/planet-earth/earthquakes/why-do-earthquakes-happen-far-away-from-plate-boundaries …. A good question. Why do earthquakes occur a long way from plate boundaries. The consensus idea of Plate Tectonics does not always seem to be consistent with tectonic reality. Earthuakes do not always occur where they are most expected. These are Plate Boundaries or what is known as subduction zones. There are of course numerous small fault zones all over the place. The piece, being oriented to a North American audience, chooses the New Madrid earthquake as an example. It occurred in 1811 and caused a lot of damage and deaths. It was far away from any plate boundary – although at the time, Plate Tectonics wasn’t even a twinkle in anyone’s eyes. Is it a geophysical mystery? We then get a few other geologic processes that may lie at the root of earthquakes – such as blobs moving around in the Mantle, former glaciated regions still rebounding, fracking [the injection of water, sand and chemicals to get oil and gas moving from underground reservoirs], and mining. That sort of thing. All we know is they happen. They will happen again.

At https://www.livescience.com/planet-earth/geology/earth-may-have-had-freshwater-and-continents-just-200-million-years-after-forming-ancient-crystals-reveal …. this one is a surprise – and somewhat contradictory. Earth’s continents may have emerged from Earth’s primeval oceans much earlier than the mainstream view currently allows. Ancient zircon crystals from Western Australia contain evidence of fresh water.

The composition of early Earth is conjecture. It is assumed to have begun as a roiling sphere of magma that eventually solidified to form the crust. It is unclear how water arrived on our planet. Or was it part of the planet’s original make-up. Did water arrive from outer space – comets, asteroids or meteors. Fresh water could only have been present as part of a hydrological cycle – evaporation and precipitation. Rain water contains lighter isotopes and evaporates more easily than sea water. The zircon crystals contained high levels of light oxygen isotopes – forming whern magma rose to the surface and interacted with fresh water. Its a bit more complicated than that but zircon crystals seem to show the standard model of the formation of the Earth may not be all it is cracked up to be.

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