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The magnitude 8.9 offshore quake unleashed a 7-meter tsunami and was followed by more than 50 aftershocks for hours, many of them of more than magnitude 6.0. Scientists say the massive earthquake ranks as the fifth largest jolt in the world since 1900, shaking after the initial shock lasted for about five minutes. (Graphic News)
The magnitude 8.9 offshore quake unleashed a 7-meter tsunami and was followed by more than 50 aftershocks for hours, many of them of more than magnitude 6.0. Scientists say the massive earthquake ranks as the fifth largest jolt in the world since 1900, shaking after the initial shock lasted for about five minutes. (Graphic News)

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Q&A: Expert explains science behind earthquakes and tsunamis Add to ...

University of Ottawa engineering professor Ioan Nistor answers questions about the earthquake and tsunami that hit Japan and other Pacific coastal regions.

Linda Stewart: I have a question: was there no pre-warning that the earthquake was going to hit, as well as to its potential severity?

Dr. Ioan Nistor: There is tsunami early warning system, based in Palmer Alaska and Hawaii. The alarm probably worked, Japan is very prepared from this point of view. But because of the proximity of the earthquake to the shoreline gave very little time to evacuate. In the case of Hawaii, there was much more time for people to evacuate.

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Alison Teasdale: If you lived in Japan I am sure you are aware that Japan has an advanced tsunami warning system and a lot of effort is put into disaster prevention. Was it just the size of this earthquake, or were there some other factors that made this tsunami so deadly?

Dr. Ioan Nistor: Proximity to the shoreline and the magnitude of the quake and the vertical uplift of the quake. The height of the tsunami wave and the fact it was very close to the shoreline gave little time to evacuate. The amount of damage would have been the same but people would have had more time to evacuate. The waves travelled with limited energy dissipation to the Japanese coastline as well.

MaryMary: Is there any relationship between this earthquake and the recent New Zealand earthquake? Are we in an period of increased earthquake risk?

Dr. Ioan Nistor: No, there is no relation. We don't have any way to predict periods of increased earthquake risk either.

tom50mgtom50mg: Good day,what is the potential risk for the west coast of Vancouver Island.

Dr. Ioan Nistor: There are 2 different kinds of risks for the west coast - you can have risks associated with distant earthquakes and subsequent tsunamis. Distant quakes and tsunamis can travel across the ocean and impact those areas. However a bigger danger is the presence of the Cascadia subdaction zone which has generated in the past tsunamis, messy tsunamis in fact, that affected the coastline of B.C. The subdaction zone is a fault line that is very similar to the one that is off the coast of Chile.

Ewa SasEwa Sas: What about the cruise ships in Pacific/Hawaii area?

Dr. Ioan Nistor: If you are on a cruise ship in the middle of the ocean in deep water conditions, you would not feel that tsunami. So someone in deep water conditions would not see or feel that tsunami. A tsunami is travelling a few hundred kilometres an hour and its wave height is a few centimetres. They can only be felt by deep water wave gauges which are part of the tsunami warning system. But if you are in a port close to the shoreline, the waves change characteristics as they approach the shoreline so then you would feel it. A lot of the time in tsunami alerts, ship leave harbours and go offshore.

DennisDennis: Any floating monitors out in the ocean to warn us?

Dr. Ioan Nistor: Very simply put, in the ocean there are a number of pressure transducers or wave gauges that are placed on the bottom of the ocean and they can record the presence of tsunami waves, which you can't do in a boat. These sensors are connected to buoys on the surface that are connected to a satellite system so they can send information in a very short time about a tsunami wave passing over them.

MichelleMichelle: How will the tsunami impact southern tip of Vancouver Island (Victoria and westshore)? Should we be concerned?

Dr. Ioan Nistor: Tsunamis have impacted that region in the past. The big danger is a big tsunami produced by the Cascadia fault. So a dangerous situation could occur if a major earthquake was produced by this fault. The time for evacuation would be relatively short since the fault is close to the shoreline. That's the danger, particularly for Vancouver Island and Victoria.

PatPat: Do you know when (if it all) the impact on Vancouver will occur? In other words, are you able to estimate when it will occur?

Dr. Ioan Nistor: The arrival time calculation is very accurate. It's in the order of minutes almost. What is not accurate is the wave height at a certain location. The research has demonstrated that we can predict the arrival time within minutes. What we can't predict is the height of the tsunami. We would have to cover the whole floor of the ocean with sensors to detect what is the vertical displacement, but that is virtually impossible.

VijayaVijaya: If a huge wall had been built along the coast of Japan could it have kept the tsunami out or at least reduced its force?

Dr. Ioan Nistor: In fact there are a few locations in Japan where sea walls have been built to predict against tsunami. However, they can only be placed in certain locations like narrow bays. The costs associated with building such a structure are enormous.

 

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