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The Combination of Earthquake Zone and Volcanic Systems at Reykjanes

It can be confusing when seismic and volcanic activity is intervowen as at the Reykjanes Peninsula. Luckily, we have good information about the tectonic drift in the area, measured with GPS technology. The results are found in this report https://www.lmi.is/static/files/utgefid_efni/Maelingar/isnet_endurmael_2016_skyrsla.pdf.

On this map, I have superimposed the grid on the original map from the Icelandic Land Survey showing tectonic drift vectors.

Reykjanes Peninsula in context with convection rolls grid and tectonic drift vectors.

The drift vectors show the rotation taking place within the Reykjanes polygon. Further analysis provides this drawing:

The Reykjanes Earthquake Zone and a few relevant dynamic factors.

The small black arrows indicate the unaltered drift directions measured directly with GPS stations. It can be reasoned that the rifting process of the volcanic systmes is perpendicular to the main tensional effect within the area, indicated with light gray arrows. Similarly, pressure is excerted, creating the earthquake faults with NS alignment. The western half of the polygon seems to rotate in a semi-circular way with center at its western corner, but is at the same time subject to rifting process to the west. Similarly, the eastern half is subject to rifting to the east as compared to the NS axis of the polygon.

The earthquakes at Reykjanes Peninsula show resemblance to the volcanic systems, but occur on NS faults. This should be due to an interplay between tension and pressure within the polygon.

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Reykjanes Earthquake Zone in 3D

To realize what forces are affecting the earthquake zone of Reykjanes, a 3D model can be useful. The convection rolls below interact with the basic tectonic drift. Layer A has direct contact with the ductile part of the tectonic plate. Layer B has a certain degree of coupling effect with layer A, also affecting the tectonic plate. The ductile part is twisted as a result, turning anti-clockwise. Therefore, the polygon forms a rupture along the NS-axis from one corner to the other. This leads to the fact that the brittle part above may be affected by the twisting effect from below at different points of time at each side of the NS-axis.

The earthquake zone of Reykjanes Peninsula

The convection rolls are nearly perpendicular to each other. Drawn to scale. The coupling effect between layers leads to different pressure and tectonic drift directions, besides earthquakes.

The relevant earthquake swarm is shown in the previous post.

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An Earthquake Swarm of Reykjanes Peninsula

Comparing the unique earthquake swarm occurring today with the mathematical continuation of Reykjanes Ridge and the relevant mantle convection rolls, this pattern emerges:

Reykjanes earthquake swarm 1/4 pattern.

The earthquake swarm spans over an area within one quarter of the polygon. The faults pattern of the South Iceland Seismic Zone are shown for comparison. The faults continue into the Reykjanes Polygon, but due to the swaying effect of the central axis of the seismic zone system, the faults are likewise forced to appear farther to the south. The faults remain NS oriented within the Reykjanes part of the seismic system. Earthquake seem to occur mainly south of the central tectonic division line, as can clearly be seen on this map. The NS axis of the polygon is surprisingly decisive, resulting in a ‘1/4 pattern’ of the swarm.

Red lines show upwelling, blue lines show downwelling. The polygon is simplified and superimposed on a map from the National Land Survey of Iceland.

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Reykholt and Snorralaug

Extending the Reykjanes Ridge mathematically, it does cross the most powerful low temperature geothermal area of Iceland of Reykholtsdalur. A division line is found under the farm Reykholt.

The position of Reykholt and some other scenic areas.

The pool at Reykholt is quite famous. Snorri Sturluson, the most famous writer of Iceland, lived there in the 13th century.

Snorralaug

The hot water flows into the pool Snorralaug, translated as Snorri’s Pool, from the hotspring Skrifla.

Skrifla

The system was quite advanced, because steam was led from this hotspring through a pipeline into Snorri’s farm, heating the floor inside it.

Snorri Sturluson was the richest and most powerful man in Iceland, and did choose a fabulous place as his home.

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The Convection Rolls System of Japan

Japan is known for volcanoes and hot springs, and having a critical position between different tectonic plates. The conditions within the mantle should add to that story. Division between large convection rolls is expected to be located under Japan, affecting the smaller convection rolls of the asthenosphere.

The convection rolls system of Japan (base map from japanvolcano.wordpress.com)

One convection roll is highlighted here with red, because a large number of volcanoes happens to be located within that area. This volcanic roll, swaying towards NE, is found at the depth of around 120-265 kilometers. The rolls underneath, swaying towards NW, are at the depth of 265-410 km. Below 410 km, the large convection rolls of lower mantle are found. As the large scale lower mantle division line is found under the highlighted roll of the asthenosphere, the importance of that roll becomes more understandable. To fully understand the geology of Japan, both the tectonic drift of the converging plates and the relevant mantle currents have to be considered, to see how these factors interact with each other.

Note the location of Fuji, is directly above the division lines of two layers (and the division line of the lower mantle as well).