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    Default Mega Earthquakes Mystery solved

    Finally, a sane approach to the location areas of these infrequent mega earthquakes is being presented in this paper:

    The link between great earthquakes and the subduction of oceanic fracture zones
    http://www.solid-earth.net/3/447/2012/se-3-447-2012.pdf

    by R. D. Müller and T. C. W. Landgrebe

    Abstract. Giant subduction earthquakes are known to occur in areas not previously identified as prone to high seismic risk. This highlights the need to better identify subduction zone segments potentially dominated by relatively long (up to 1000 yr and more) recurrence times of giant earthquakes.

    We construct a model for the geometry of subduction coupling zones and combine it with global geophysical data sets to demonstrate that the occurrence of great (magnitude 8) subduction earthquakes is strongly biased towards regions associated with intersections of oceanic fracture zones and subduction zones.
    ************************************************** ****************

    The rest of the paper substantiates the claims in the abstract and... that's that!

    Here is the summary picture of their research:

    Fig. 1. Data sets used in this study superimposed on the ETOPO1 global relief model (Amante et al., 2009), on a Robinson projected map:
    subduction coupling zones (blue bands) (see text for coupling zone model description), oceanic fracture zones (dark gray) and oceanic volcanic chains and aseismic ridges (pink) (Matthews et al., 2011), intersection points of fracture zones with subduction zones (yellow squares), intersection points of the volcanic chains and ridges with subduction zones (green squares), largest 15 instrumentally recorded earthquakes (Mw  8.6) (red stars), largest 50 earthquakes (Mw  8.4) (light blue circles), and all other significant earthquakes (small beige circles) (NGDC/WDC, 2011). Inv FZ, Investigator Fracture Zone, Krus FZ, Krusenstern Fracture Zone, Phil SZ, Philippine Subduction Zone, Mar SZ, Marianas Subduction Zone, SW-P SZ, Southwest Pacific Subduction Zone, Jap SZ, Japan Subduction Zone, Kam SZ, Kamchatka Japan Subduction Zone, Aleu SZ, Aleutian Subduction Zone, Cas SZ, Cascadia Subduction Zone, C-Am SZ, Central America Subduction Zone, S-Am SZ, South America Subduction Zone, L-An SZ, Lesser Antilles Subduction Zone.



    Fig. 4. Three great earthquake rupture case studies for (a) the 2004 Mw = 9.1 Sumatra-Andaman Earthquake (Robinson, 2007) and (b) the 2001Mw = 8.4 Peru earthquake (Robinson, 2007) depicting the modelled rupture process through time for 5m slip contours, and (c) the 1986 Mw = 8.0 Andreanoff islands earthquake (Das and Kostrov, 1990) showing the modelled rupture process through time for a momentmagnitude contour of 3×1020 Nm. Earthquake epicentres are shown as red stars, overlain over vertical gravity gradient maps (Sandwell and Smith, 2009), with fracture zone locations (Matthews et al., 2011) shown as yellow dashed lines, with their interpreted coupling zone extensions outlined in faint yellow dashes. Coloured polygons illustrate the progression of the rupture process relative to the inception at the epicentre, providing a visualisation of the role that the fracture zones played during the event.

    Inset plots show ship bathymetry (top) and gravity anomalies (bottom) along magenta profiles crossing key fracture zones, with red arrows indicating fracture zone location. The seismically imaged Simeulue ridge (Franke et al., 2008), associated with the subducting 96 Fracture Zone (Kopp et al., 2008), is outlined as black dashed line.

    ************************************************** ****************

    So, according to this research, if there is another big one to happen, the most probable location for that one is at one of these intersections where one hasn't occurred in a long while.
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    Default Re: Mega Earthquakes Mystery solved

    I want to show you something since you are interested in this and well educated.
    Before I found your post (looking for correct place for image), I made this and wondered if it was a good explanation for why Vanuatu always shakes before PNW/oregon microplate:



    i don't want people to really think i want it to happen in PNW although i have said that at times.


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    Default Re: Mega Earthquakes Mystery solved

    Hi T_WTC_S,

    I don't have the data indicating that there is some statistical correlation between Vanuatu shaking and the PNW shaking.

    All I can provide is this map of the plates velocity vector with respect to Africa taken as immobile:



    This map demonstrates that the bulk of the subductions occuring on earth happens mostly at the western edge of the Pacific Ocean with a cumulated 1 meter/year being subducted compared to 0.26 meter for the PNW. Hence, BIG ones are more likely to happen at the western edge of the Pacific Ocean than anywhere else. In second place comes South America and then, marginally, North America.

    The above paper gives a finer definition for the areas where such BIG ones are likely to occur.
    "La réalité est un rêve que l'on fait atterrir" San Antonio AKA F. Dard

    Troll-hood motto: Never, ever, however, whatsoever, to anyone, a point concede.

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    Default Re: Mega Earthquakes Mystery solved

    Quote Posted by Amzer Zo (here)
    Hi T_WTC_S,

    [...]

    ... BIG ones are more likely to happen at the western edge of the Pacific Ocean than anywhere else. In second place comes South America and then, marginally, North America.

    The above paper gives a finer definition for the areas where such BIG ones are likely to occur.
    To wit:
    Take a peek at this post to get an idea of how long this compounded EQ (7.3 + 6.2 13 minutes apart) has shaken the ground at some distance around, i.e. Tokyo:

    http://projectavalon.net/forum4/show...l=1#post594667

    The La Gomera station recorded it for over an hour!
    "La réalité est un rêve que l'on fait atterrir" San Antonio AKA F. Dard

    Troll-hood motto: Never, ever, however, whatsoever, to anyone, a point concede.

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