Alpine Fault

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The Alpine Fault

Investigate the evidence relating to geological event(s)

Micheal Munro

AS91412

Intro
The Alpine fault is the boundary of the Pacific oceanic plate and the continental Australian plate. It is located almost through the entire south island of New Zealand extending about 600 Km across it1. It is one of the world’s major geological features and is responsible for the amazing Southern Alps. Each time it has ruptured it has moved both vertically as well as horizontally. Some believe it has lifted the Southern Alps in the process up to 20 kilometres in the last million years but cut down in height by erosion2.

The Alpine Fault is a strike slip fault. In this case the Australian plate is sliding horizontally towards the northeast, at the same time as the pacific plate is pushing up forming the Southern Alps, raising them 7 millimetres each year.10 The Horizontal movement along the fault is not smooth, as both sides are locked together. When tectonic forces overcome this locking the fault slips, jumping up to a distance of 8 metres at a time. This is what causes the earthquakes of the Alpine Fault. The alpine fault was originally believed to be responsible for four major ruptures in the last 1000 years. These occurred in approximately 1100, 1450, 1620 and 1717 CE, at intervals between 100 and 350 years. These ruptures were as big as magnitude 8 on the Richter scale3. Since the rupturing of the Alpine fault is believed to be reoccurring in a pattern, scientists believe that the Alpine fault is likely to go off in the next 50 years. This would ultimately cause unthinkable devastation. This is why the dating of the Alpine fault is important. Because the more accurate the dating of the previous ruptures the more accurate they can predict the next rupture. This is why scientists are comprehensively studying the Fault with urgency. It is right under our feet, a ticking time bomb.

History
Harold Wellman first discovered the Alpine fault. Harold Wellman is a geologist with a more varied experience than most. He first came to New Zealand from Britain in 1927 when he was 18, and soon found steady work as a surveyor's assistant. In 1932, he obtained his own ticket as a registered surveyor4

Harold Wellman not only recognised one of the most extraordinary geological structures in New Zealand, but his insight into what must have happened there helped set off a revolution in science. It helped change the way we think about the way the Earth works.5

In 1941 Harold and fellow geologist Dick Willet were interested to see how far they could trace the Gregory Valley southwards for geological observations. They found several exposures of the fault itself where the rock was pulverized and Wellman noted that," The broken schist looked like the result of explosions, or perhaps we were seeing the heart of old earthquakes." They soon realized they had been following a giant fault that was at least 200 km long, they called it the Alpine fault.

Immediately east of the fault, the greywacke and schist of the Southern Alps have been raised many thousands of meters. Within the Arc rocks in The southland area is a narrow belt of dark greenish rocks rich in the minerals olivine and pyroxene which contain a high proportion of magnesium and iron, so much iron in fact that they locally affect the earths magnetic field. The Southern Alps are composed of two primary rock types. They are greywacke interbedded with an argillite-derived pelites. Close to the Alpine Fault the rock types change to a linear metamorphic band parallel to the trend of the Alpine Fault6 The differences in these rocks are how we can tell where the Alpine fault lies.

Because of the inept accurate dating of this geological event, many dating methods are used today to evaluate the probability of a future rupture on a major fault. To do this scientists need to establish the dates and size of...
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