The Christchurch Earthquakes
Plate Tectonics
The earth is covered in a crust called the lithosphere. This crust is not complete; it is split up into different pieces called plates. These plates move around the earth, and they sometimes collide. These collisions have different names, depending on what occurs:
* A divergent boundary is when two plates move away from one another and magma is forced up from the mantle to fill the gap.
* A convergent boundary is when is when two plates move towards one another; in this case one plate is usually forced underneath the other and is melted by the mantle underneath.
* The last category of boundary collision is a transverse boundary. This is when the plates are being scraped alongside each other.
http://gzscienceclassonline.weebly.com/116-christchurch-earthquakes1.htmL
The Christchurch earthquake in September the 4th 2010 and its aftershocks were caused by plate tectonics such as these, the two plates involved collided in an transverse collision.
* A divergent boundary is when two plates move away from one another and magma is forced up from the mantle to fill the gap.
* A convergent boundary is when is when two plates move towards one another; in this case one plate is usually forced underneath the other and is melted by the mantle underneath.
* The last category of boundary collision is a transverse boundary. This is when the plates are being scraped alongside each other.
http://gzscienceclassonline.weebly.com/116-christchurch-earthquakes1.htmL
The Christchurch earthquake in September the 4th 2010 and its aftershocks were caused by plate tectonics such as these, the two plates involved collided in an transverse collision.
September 4th Earthquake 2010.
The Pacific and the Indo-Australian plates have a fault line running along between them. This fault line crosses through the South Island of New Zealand. On September 4th 2011 they caused an earthquake near Christchurch, which caused great destruction. The Pacific and the Indo-Australian plates ground together transversely. This is called a transform collision. These plates have been colliding for centuries and so there have been many earthquakes of various strengths. The 2010 earthquake's epicentre was 40km away from Christchurch, near to the town of Darfield.
http://en.wikipedia.org/wiki/2010_Canterbury_earthquake
http://gzscienceclassonline.weebly.com/
After this initial quake the ground continued to shake however... this is the crust reassembling itself after breaking. On February the 22nd and unusually large aftershock occurred and was at first thought to be a second earthquake because of its massive shake.
February 22nd Aftershock 2011.
Aftershocks are created as the fault line adjusts the crust after the effects of the main shock. Aftershocks are smaller earthquakes that are caused around the same place after a bigger earthquake. If an aftershock is bigger than the original quake, then both are renamed; the original quake is labelled the foreshock, and the aftershock is re-designated as the main shock.
The February 22nd 2011 aftershock affected Christchurch more than the original quake, because this aftershock was directly underneath Christchurch whereas the original was about 40km away.
This earthquake had a death toll of 184, and it caused more structural damage to Christchurch than the main earthquake. There was more destruction of buildings as most buildings were already weakened by the original quake, and more liquefaction occurred as the crust was already broken.
http://en.wikipedia.org/wiki/Aftershock
http://www.gns.cri.nz/Home/News-and-Events/Media-Releases/earthquake-part-of-aftershock-sequence
In both these earthquakes there was a series of phenomena, starting when the two
plates collided together. The first sensation people experienced was the
noise.
The Sound Of The Primary Waves.
People began to hear a loud rumble before the shaking began because primary waves travel faster than secondary and surface waves. Primary waves are compression waves that shift the ground from side to side. These waves are hard to feel underfoot, but can still be heard. This is the rumbling people heard before the shaking of the secondary waves.
http://gzscienceclassonline.weebly.com/116-christchurch-earthquakes1.htmL
Primary waves are not the only kind of seismic waves created by an earthquake, however...
http://gzscienceclassonline.weebly.com/116-christchurch-earthquakes1.htmL
Primary waves are not the only kind of seismic waves created by an earthquake, however...
Seismic Waves
Seismic waves are shock waves caused at the epicentre of an earthquake when two plates collide. They cause the ground to shake dramatically, because more than one wave is set off at once; together they shake, break, and weaken both the surface and underground structure. Primary waves shift the ground back and forth and only appear at the beginning of an earthquake. Secondary waves shift the ground up and down and appear until the earthquake is finished, but they are slower than the primary waves. Surface waves are also slower than primary waves; they roll along the ground like churning ocean waves, and shift the ground from side-to-side.
http://gzscienceclassonline.weebly.com/116-christchurch-earthquakes1.htmL
When these waves shock the ground they compress some areas and loosen up others. This disturbs the granular layers containing water, and liquefaction occurs.
When these waves shock the ground they compress some areas and loosen up others. This disturbs the granular layers containing water, and liquefaction occurs.
Liquefaction.
Liquefaction is when saturated soil or sand is put under substantial stress, and looses its form and stiffness. This causes it to behave in a liquid form, making the soil equivalent to quick sand. This may cause the liquefied soil to be forced up to the surface, (as the diagram indicates) or to give way and cause a landslide. After the September 2010 earthquake people cleared 30,000 tonnes of mixed sand and mud from around residential areas alone. In the February 2nd earthquake, ESL News estimates that there was about 150,000 tonnes of liquefaction cleared (five times the amount in the original earthquake). When this "quicksand" dries it turns into dust which gets into the lungs, eyes, and mouth. http://geology.isu.edu/wapi/envgeo/EG5_earthqks/images/liquefaction.gif
http://en.wikipedia.org/wiki/Soil_liquefaction
After all of this damage from both waves, and liquefaction Christchurch had to pay for the repairs. Not only did they pay in money, but through out the quake, and aftershocks they paid in lives.
http://en.wikipedia.org/wiki/Soil_liquefaction
After all of this damage from both waves, and liquefaction Christchurch had to pay for the repairs. Not only did they pay in money, but through out the quake, and aftershocks they paid in lives.
The Cost to Christchurch
During the February 22nd aftershock many people were injured, 184 were killed, and thousands of homes were destroyed by both liquefaction and shaking. Roads were broken and covered in mud, and the central city was ruined and mis-aligned. 10,000 houses had to be pulled down and rebuilt. The economic impact of the Canterbury earthquakes was estimated by Miles Parker and Daan Steenkam: the "final nominal cost of the rebuild is likely to be higher than the $20 billion figure". The Canterbury Earthquake Recovery Authority’s (CERA) figures suggest that "the rebuild, improvements included, could total $30 billion" (Brownlee 2012).
http://www.rbnz.govt.nz/research/bulletin/2012_2016/2012sep75_3parkersteenkamp.pdf
http://wiki.answers.com/Q/What_did_the_christchurch_earthquake_affect_the_people
http://www.rbnz.govt.nz/research/bulletin/2012_2016/2012sep75_3parkersteenkamp.pdf
http://wiki.answers.com/Q/What_did_the_christchurch_earthquake_affect_the_people