Question3 (a) In February 2011, the city of Christchurch (New Zealand) experienc

Question

Question3 (a) In February 2011, the city of Christchurch (New Zealand) experienced an earthquake of magnitude 6.3 that caused much damage and many deaths. Yet in September 2010, Christchurch experienced an earthquake of magnitude 7.1 that caused less damage and no deaths. Explain some of the reasons why the smaller February 2011 earthquake was more damaging 5 marks) (b) Explain how the grain size of deposited sediments changes moving from the upper reaches of a river to its delta with the sea. What are the geotechnical implications of this systematic change in grain size in terms of the stability of the sediments as a substrate for structures? (5 marks)

Explanation / Answer

A. The Earthquake in the city of Christchurch (New Zealand) on February 2011 experienced 6.3 magnitude but caused much damage and deaths compared to September 2010 where the same city experienced an earthquake of 7.1 magnitude but resluted in less deaths.

This is because of THE TIME IT OCCURRED. The February 2011 Earthquake occurred during mid afternoon lunch time so many people were on streets for food and thus unfortunately almost 190 people were killed in the February 2011 Earthquake. The September 2010 Earthquake occurred during midnight where no people are in streets so there is no loss of life.

To make it simple for you:

1. SEPTEMBER 2010 --- OCCURRED DURING MIDNIGHT, PEOPLE ARE NOT IN STREETS( NO LOSS OF LIFE)

2. FEBRUARY 2011 --- OCCURRED DURING AFTERNOON, MIDDLE OF WORKING DAY(190 PEOPLE WERE KILLED)

B. Sediment movement or transport is the movement of organic and inorganic particles by water. Generally if the flow is greater, the more and more sediments will be conveyed and also strong water flow is capable enough to suspend particles in the water columns as they move towards downward stream. In this Sediment deposition the suspended particles settle down to the bottom of a body of water. Suspended soil is sampled at several heights and positions on river and due to the pull of gravity the particle tends to settle to the bottom. The prolonged transport of sediment by water can affect the particle and REDUCTION IN THE PARTICLE SIZE CAN BE OBSERVED. The greater the distance of transport, the smaller and more rounded are the grains.

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