Number of Waves/Crests in Tsunami Wave Train

[morrobay]

Homework Statement

An event 1600km offshore produces a Tsunami. Wavelength= 200km Velocity = 800km/hr. How many waves in the wave train ?

Relevant Equations

k= 2pi/wl = .0314 radians. T = wl/v = .25 hr. w = 2pi/T = radians/hr.

In the two hours the wave is traveling from event 1600km offshore to land would eight waves/crests be produced: 2hours/T=15minutes be correct ? Eight cycles = eight waves in the train. * I asked on another physics forum. No reply. "Tried" to register on several oceanography forums.

 

[Tom.G]

from: https://www2.tulane.edu/~sanelson/Natural_Disasters/tsunami.htm

A tsunami can have a period in the range of ten minutes to two hours and wavelengths greater than 500 km.

(above found with:
https://www.google.com/search?&q=wavelength+of+tsunami)

Cheers,
Tom

 

[Delta2]

Homework Statement:: An event 1600km offshore produces a Tsunami. Wavelength= 200km Velocity = 800km/hr. How many waves in the wave train ?
Relevant Equations:: k= 2pi/wl = .0314 radians. T = wl/v = .25 hr. w = 2pi/T = radians/hr.

In the two hours the wave is traveling from event 1600km offshore to land would eight waves/crests be produced: 2hours/T=15minutes be correct ? Eight cycles = eight waves in the train. * I asked on another physics forum. No reply. "Tried" to register on several oceanography forums.

I think you are correct. With the given data the period is indeed 1/4 of an hour and within the two hours it does to travel to the shore, there will be $8=\frac{2}{\frac{1}{4}}$ full waves produced.

It was just a bit vague the way you stated the problem, asking just for the wave train. You meant the wave train that is formed, till the tsunami hits the shore.

PS. Then again, there is something fishy here. If we going to take it that 8 full waves are produced within 2hours this means that the seismic activity that produces the tsunami continues for 2hours as well, which I don't know if it is something valid.

 

[morrobay]

I think you are correct. With the given data the period is indeed 1/4 of an hour and within the two hours it does to travel to the shore, there will be $8=\frac{2}{\frac{1}{4}}$ full waves produced.

It was just a bit vague the way you stated the problem, asking just for the wave train. You meant the wave train that is formed, till the tsunami hits the shore.

PS. Then again, there is something fishy here. If we going to take it that 8 full waves are produced within 2hours this means that the seismic activity that produces the tsunami continues for 2hours as well, which I don't know if it is something valid.

The seismic event can be only seconds duration. What continues for 2 hours are all the waves produced reaching land. The first wave reaches land in two hours then every 15 minutes waves 2 through 8. So a total of four hours for the complete wave train . Again this is assuming that each cycle is a wave. And all above is not taking into account the change in velocity with ocean depth. An oceanographer would be required for an exact answer accounting for all the variables . I am just asking for the standard conditions answer.

https://ocean.si.edu/planet-ocean/waves-storms-tsunamis/anatomy-wave

 

[Delta2]

What continues for 2 hours are all the waves produced reaching land

Sorry I am not an oceanographer but I can't understand how the seismic event can be only seconds, but waves will be produced for 2 hours...

 

[morrobay]

This is the original question. Does each of the eight cycles constitute a wave. Or is it one wave with eight cycles.

 

[Delta2]

This is the original question. Does each of the eight cycles constitute a wave. Or is it one wave with eight cycles.

I don't very much understand the question. It's more or less the same thing to me.

 

[morrobay]

I don't very much understand the question. It's more or less the same thing to me.

Will one wave hit beach or eight waves. Seems now one is correct

 

[Delta2]

Will one wave hit beach or eight waves. Seems now one is correct

If eight waves are produced then eight will hit the beach, I just doubt that all eight are being produced since the source is active only for a few seconds. I have an analogy in mind, when a stone falls into the surface of a pool then the collision lasts only for a few milliseconds but only one or two full waves are produced I think.

 

[morrobay]

If eight waves are produced then eight will hit the beach, I just doubt that all eight are being produced since the source is active only for a few seconds. I have an analogy in mind, when a stone falls into the surface of a pool then the collision lasts only for a few milliseconds but only one or two full waves are produced I think.

These are photos of a video I made that uploads but cannot post. One rock dropped into the pool produced multiple waves.

 

[Delta2]

Ok well I just don't know, I am a mathematician that knows something about classical wave theory but I am no expert in water waves and tsunamis. Just wait a little longer, maybe this thread will attract the attention of more people and possibly some experts.