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Earthquake in New Zealand

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The New Zealand is a seismic risk area high. During the night of Sunday 13 to Monday, November 14, 2016, she suffered an earthquake of a magnitude of 7.6. Occurred at only 23 km depth, the earthquake woke up number of inhabitants and reminder as soon as the memory of the earthquake of magnitude 6.3 that killed 185 in 2011 in the Christchurch area. A few hours later, a second quake of magnitude 6.2 again undermined the country. Monday day saw a dozen of weaker aftershocks.

How does an earthquake?

An earthquake or an earthquake is the release of energy accumulated during the tectonic movement of plates. In a fault, on an area of contact, the pressure is so strong between the two plates that the movement will lead to an accumulation of energy. The contact points will not move during the movement of the plates which accumulate energy. And a moment, we’ll have a break that will liberate all that energy! It is at this time the creation of a shock wave and so of an earthquake.

Diagram of the origin of an earthquake. The movement of the plates causes a collision between points A and B. During the violent separation of these two points, energy is released resulting in the creation of an earthquake.

The release of stored energy is generally not in a single jolt. In general, it can occur several tremors during the liberation of energy. Thus, there were aftershocks following the main shock of an earthquake and decreasing amplitude, over a period ranging from a few minutes to more than a year. In New Zealand, it is produced on more than one day. The aftershocks are sometimes more devastating than the main shock, because they can cause damage on infrastructure which had only been damaged. It can also occur a more powerful than the main tremor replica regardless of its magnitude. For example, an earthquake of 9.0 may be followed by a replica of 9.3 months later even if this sequence is extremely rare.

Diagram of the origin of an earthquake

The seismic zones are characteristic of unstable geological areas. The New Zealand is located in a subduction zone, that is why we have a strong volcanic activity and many earthquakes.

Movement of the plates in the world. The subduction between two plates is observed for the new-Zealnde,

The Tsunami, consequence of the earthquake

The Tsunami (from a Japanese term) comes from a sudden and significant seabed movement during an earthquake. Seismic waves cause movements of water. This causes a second movement called of wavelength (usually a few hundred kilometres) and large period (a few minutes in the case of a landslide to a few tens of minutes in case of an earthquake).

Creating a tsunami by a seismic wave propagation

Some tsunamis are able to propagate over distances of thousands of kilometres and the entire coast from coast-to-coast in less than a day. The speed is generally between 500 and 700 km/h but can exceed 800 km/h. These large tsunamis are usually of tectonic origin, because landslides and volcanic explosions generally produce waves of shorter wavelength which dissipate quickly: we’ll talk about dispersion of waves.

Ring of fire

The New Zealand lies on the “ring of fire” in the Pacific ocean. One of the more active areas geologically of the world. It is for this that she has many hot springs and is made up mostly of volcanic rock.

ring of fire
Presentation of the ring of fire. You can see a resemblance between the ring of fire and the boundaries of the plates of the previous card.

The ring of fire is so called because it represents an alignment of volcanoes in the Pacific ocean. More than 75% of the world’s volcanoes are located in the Pacific ocean. Most of the volcanoes are located on the boundaries of tectonic plates of the ocean. These limits coincide with subduction zones, such as the Andes, the fault of San Andreas and the New Zealand for example. This game of tectonic plates is also the origin of frequent earthquakes (90% of the earthquakes and 80% of the largest earthquakes).

For all definitions: go to this page.
For the time scale is here!


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