Uplifted island: the document of a complete seismic cycle

Posted: June 25, 2015 by oldbrew in Earthquakes, Geology

Sea lions get a lift in Chile [credit: M.Moreno/GFZ]

Sea lions get a lift in Chile
[credit: Daniel Melnick/I.B.Times]


The island Isla Santa María in the south of central Chile is the document of a complete seismic cycle, reports phys.org:

Charles Darwin and his captain Robert Fitzroy witnessed the great earthquake of 1835 in south central Chile. The “Beagle”-Captain’s precise measurements showed an uplift of the island Isla Santa María of 2 to 3 meters after the earthquake. What Darwin and Fitzroy couldn’t know was the fact that 175 years later nearly at the same position such a strong earthquake would recur.


At the South American west coastline the Pacific Ocean floor moves under the South American continent. Resulting that through an in- and decrease of tension the earth’s crust along the whole continent from Tierra del Fuego to Peru broke alongside the entire distance in series of earthquakes within one and a half century. The earthquake of 1835 was the beginning of such a seismic cycle in this area.

After examining the results of the Maule earthquake in 2010 a team of geologists from Germany, Chile and the US for the first time were able to measure and simulate a complete seismic cycle at its vertical movement of the earth’s crust at this place.

In the current online-edition of Nature Geoscience they report about the earthquakes: After the earthquake of 1835 with a magnitude of about 8,5 Isla Santa María was uplifted up to 3 m, subsided again about 1,5 m in the following 175 years, and upliftet anew 1,5-2 m caused by the Maule earthquake with a moment magnitude scale of 8,8.

Full story: Uplifted island.
Science paper – ‘Vertical deformation through a complete seismic cycle at Isla Santa María, Chile’

H/T SIS group: Uplifting
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Let’s add a little twist to this just for discussion purposes: here’s a graphic from the solar simulator. Planets other than Uranus, Neptune and Earth have been excluded. What we’re focussing on is the length of the seismic cycle, given as 175 years.

[click to enlarge]

[click to enlarge]

Comments
  1. oldbrew says:

    Cycles need causes😐

  2. ALecM says:

    Clever!

  3. oldbrew says:

    The 1835 earthquake would have been about 14 years after the Uranus-Neptune-Earth triple conjunction of 1821 and the 2010 quake came 17 years after the 1993 U-N-E line-up.

    Possibly the relative positions of the Sun and/or Jupiter and Saturn also played a part [click on graphic to enlarge].

  4. hunter says:

    The uplift, as a great demonstration in support of tectonics, is interesting. The planetary alignment seems much to random and arbitrary to be more than patter forcing.

  5. oldbrew says:

    hunter: Perhaps but the triple conjunctions do occur every 171 years. On a long-term basis the ratio of U-N-E triples to U-N conjunctions would be 62:61 so they would drift in and out of phase slightly.

    Hard to be precise when we’ve only got two occurrences recorded. Also there could be a significant ‘delay factor’ between a planetary alignment causing a seismic disturbance, and the resulting earthquake(s).

  6. Bloke down the pub says:

    On the assumption that the Nazca plate is moving under the South American plate at a steady rate, and that the makeup of the rock there allows for a relatively consistent amount of tension to build up before it has to be released by an earthquake, the null hypothesis would be that these uplifts would occur at regular intervals without any extra-terrestrial assistance.