Question

An earthquake originating in Edmonton, Alberta, Canada produces a wave that has a period of 0.23 seconds and a wavelength of 57 m. ?

a. How long will it take for this earthquake to travel a distance of 435 km?
b. Would the people in Calgary, Alberta, Canada realistically have time to get out of a house if they were notified the second the quake originated? Support your answer with logic AND a calculation.
c. Is this a realistic situation? Why or why not?

Answer 1

a. We know that velocity `v`, frequency `n` and wavelength of a wave can be expressed through the following relation
`v=nlambda`
Inserting given values. Also knowing that `n=1/T`, where `T` is time period of the wave.
`v=1/0.23xx57`
`=>v=247.83ms^-1`
Time taken to travel a distance of `435km=(435xx1000)/247.83`
`~~29min and 15sec`

b. The shortest distance (bird flight) between Edmonton and Calgary is `281 km`.
`:.`Time taken to travel a distance of `281km =(281xx1000)/247.83`
`~~18 min and 54 sec`

We see that people in Calgary have sufficient time to get out of their houses and move to a nearby safe location if they were notified the second the quake originated in Edmonton.

c. This is not a realistic situation.
Due to the reason that Rayleigh waves produced during earthquakes roll along the ground just like a wave rolls across a lake or ocean.
These are surface waves and are generated by the interaction of P- and S- (body) waves. Because of their rolling nature, these move the ground up and down, and side-to-side in the direction of movement of the waves. Most of the shaking felt from an earthquake is due to these Rayleigh waves.

Surface waves are almost entirely responsible for the destruction caused by earthquakes.

Rayleigh waves emanating outward from the epicenter of an earthquake are known to travel along the surface of earth at about `10 times` the speed of sound in air, `i.e.,` `~~3 kms^-1`.

As such people in Calgary have slightly less that `1.9 min`of time to get out of their houses and move to a safe location if they were notified immediately after the quake originated in Edmonton. Such a short time is likely to lead to a panic situation.