Tsunami

[Mowgli]

The Asian Tsunami two and a half years ago unleashed tremendous amount energy on the coastal regions around the Indian ocean. What do you think would've have happened to this energy if there had been no water to carry it away from the earthquake? I mean, if the earthquake (of the same kind and magnitude) had taken place on land instead of the sea-bed as it did, presumably this energy would've been present. How would it have manifested? As a more violent earthquake? Or a longer one?

 

I picture the earthquake (in cross-section) as a cantilever spring being held down and then released. The spring then transfers the energy to the tsunami in the form of potential energy, as an increase in the water level. As the tsunami radiates out, it is only the potential energy that is transferred; the water doesn't move laterally, only vertically. As it hits the coast, the potential energy is transferred into the kinetic energy of the waves hitting the coast (water moving laterally then).

 

Given the magnitude of the energy transferred from the epicenter, I am speculating what would've happened if there was no mechanism for the transfer. Any thoughts?

[ecoli]

Why wouldn't it behave differently than any other land earthquake?

[why06]

Well the only thing I can find different is there would be no transfer of the motion by water. Instead the air would would carry the wave of energy water would have. But since air is elastic the wave would soon dissapate and lose its power. However the sound should carry for some distance. The air wave also goes out in three dimension with out boundries while a wave throug water sonly really has two dimensions since hieght is not that much of a factor.

 

In other words:

You'll hear an above ground earthquake...

You'll just get a tsunami on a underwater one....

[ecoli]

the energy also travels through the earth's crust.

[why06]

Exactly!

I was just explaining the differences though...

[ecoli]

Exactly!

I was just explaining the differences though...

 

Would there be more energy retained in the crust without water as a medium to transfer the energy in?

 

I forget which is a better medium for transporting energy... I think water is better than air, though.

[Klaynos]

Would there be more energy retained in the crust without water as a medium to transfer the energy in?

 

I forget which is a better medium for transporting energy... I think water is better than air, though.

 

Water is better. I'd assume because the interaction between ground and air is less strong than between air and water then an earthquake on land would have more energy dissipate in the crust. But I don't know whether this would be measurable or how strong and it's just a speculation.

[why06]

I agree with with Kylanos since water has stronger intermolecular attraction. air tends to be elastic while however in water the energy is focused [is that the right word] into into a wave with a lot more momentum and power.

[Geogal]

Let’s first put a little perspective on the tsunami that was caused from the Dec 2004 earthquake off coast of Sumatra. It was about a M9.3, depending upon which magnitude scale you go by. The vast amount of energy that went into that tsunami was not from the earthquake, but actually was released from a sub-oceanic landslide triggered by the earthquake. In March 2005, a M8.7 earthquake also happened in the Sumatra area, but it did not trigger a landslide, and the tsunami was only considered of moderate size, and died out before causing great damage to anywhere far, as is often the case. Now, let’s consider the actual energy released from an earthquake. Take the Assam, Tibet 1960 eq about M8.6. It killed 780 people, destroyed 70 villages mostly by landslides, and blocked a river with landslide debris. 8 days later that broke through and killed another nearly 600 people. San Francisco 1906 about a M8.0 had the equivalent energy of about 1 billion tons of TNT or about 10 of the largest thermonuclear weapons. Scale that up to M9.3 and you’ll have about 42 billion tons TNT, or over 150 thermonuclear weapons worth of energy released. This would likely heavily damage if not destroy towns and cities within about 200km of the epicenter, or ground zero in this case, depending upon what soil or rock type these habitats were built upon. To put some perspective on this, the total solar energy received from the sun is equivalent to about 160 trillion tons of TNT, equivalent to about M12.0 earthquake, thought to be able to tear the earth apart if centered in one place.