Banks Peninsula Rising II

This video clip animation (which is silent by the way) made by GeoNet NZ is a helpful illustration of the way the New Zealand land mass has been formed between the interaction or collision between the Pacific Plate and the Indian Australian Plate. It's all interesting but what is especially interesting for the South Island is that the Southern Alps were formed by the two plates rubbing together and forcing the edges to buckle and bend and form the huge upthrusts that are now the Southern Alps.

This graphic shows the situation today. What is of particular interest is the fact that the Pacific Plate is "subducting" under the Indian Australian Plate to the north of New Zealand. ie it is diving under it. The arrow heads show where that is happening. But along the Southern Alps the edge of the Pacific Plate is apparently sliding along the edge of the Indian Australian Plate.

This difference in interaction is further illustrated in this graphic. The transverse movement/fault known as a "strike slip region" it appears. Even though the Plates are sliding along each other in the South Island, along the Southern Alpine fault, it's not as if this movement is well oiled. Any movement is in huge and violent jerks. Enormous pressures will still be exerted in an East-West direction (because the plates still press together), the edges will bind, causing a shearing stress on the Pacific Plate that lies under the Canterbury Plains. As a result a number of smaller faults have developed from the top of the South Island, parallel to the Southern Alps fault, that run down into the Canterbury Plains.

Some of these smaller fault lines are shown in this recent graphic prepared by NIWA which is now mapping new faultlines. You can just make out other red fault lines under the earthquake dots on the land around in Christchurch. It is movement in these smaller faults that give rise to smaller earthquakes (compared to those released in and by the Southern Alp fault.). But these faultlines are close to the surface and close to a city. So they can be much more destructive than a big distant earthquake.

This is an East/West cross section of Banks Peninsula (looking North). It shows the volcanic rock that formed Banks Peninsula after volcanic activity a million or more years ago. These volcanoes are extinct. The underlying rock is known to be faulted. (You can see the faultlines in the graphic.) This base rock was once flat but has been pushed up out of shape, and it has been squeezed by East-West tectonic plate pressure, and must have been cracked allowing volcanic magma to push through. One scenario is that this underlying rock is folding up slowly now. It may be a weak point in the plate. New faults may be forming. But this is speculation.

Intensive monitoring is the duty of authorities now.

Japan - Media and Plates and Earthquakes

On my flight back to New Zealand from Narita, sat next to a Japanese gentleman who was reading a Japanese newspaper. Apparently the Asahi Shimburn International version. Mostly Japanese characters as far as I could make out, but it did have quite a bit of stuff about Fukishima and the earthquake...

It has this graphic of one of the Fukishima powerstations. It's a very good graphic because it's simple. And it shows the whole thing's operation. The reactor itself is the closed cylinder within the containment vessel on the left of the graphic. It shows the fuel rods at the bottom. It also shows the cold water flowing in, getting hot, turning to steam, and then being piped to the turbine wheel. You can see that this turbine while then turns the generator, which creates electricity, which is then sent on pylon cables for use. The steam then passes for further cooling (condensation back to water), and you can see a further network of pipes at the bottom of the graphic. These will almost certainly be bringing cold seawater in to do this cooling, and the warm seawater is then discharged back into the sea. The water circulating back through the reactor - going in the bottom cold - will be fresh water. The accident at Fukishima primarily relates to the circulating freshwater escaping - as steam - and being released. Because that water passes through the reactor it will be exposed to radioactive fission materials (such as Caesium 137 and Iodine 131), and can be contaminated with those materials which pose a danger to health if the water is released into the environment. Some of that ahs happened. (see blog postings "What the F is happening at Fukishima for more")

Anyway, what was interesting was the way the newspaper also had some neat little graphics about the earthquake and about the tectonic plate movements that caused the quake. The bottom image is a graphic depiction of the fact that the tectonic plate (part of the earth's crust) upon which sit the islands of Japan (including the main island of Honshu, the northern island of Hokkaido etc, shifted or scraped across the Pacific plate, which slid beneath.

What was also interesting was the way the computer map of my plane trip showed this fault, or place where the plates are interacting. I took this photo which shows the plane I was in heading out of Tokyo. The dark chasm to the right is the Pacific faultline which was the epicentre of the magnitude 9.0 quake which hit Japan. It is interesting because all these images and signs suggest that the Japanese people are generally given a good understanding of what has caused the earthquake.

I found these next two images on Google. This one gives the names of the various plates, or sections of the earth's crust, in the vicinity of the earthquake.

And this is a great picture which further illustrates what is happening. The Pacific plate is moving westward and being subducted beneath the northern part of Japan, which is on the Okhotsk Plate. The obvious trench to the east and the mountains and volcanoes of the Japanese islands indicate that this is a place where plates converge. The Southern Alps in the South Island are also caused by upthrusts from plates converging. The epicenter of Japan's earthquake is on the offshore shelf, and not in the trench, as shown in this graphic. Earthquakes are caused by breaking and movement of rocks along the faultline where the two plates collide and slide. The earthquake moved Honshu 2.4 m (7.9 ft) east.