AAMC 7 Doppler Effect

[Ginger Ale]

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I searched the forums, but I'm still confused about this question:

"The primary rupture in the Landers quake moved from south to north as it progressed to its full 74-km length. How would the Doppler effect influence this?"

A) By decreasing the wavelength of seismic waves propagating eastward and westward

B) By increasing the wavelength of seismic waves propagating eastward and westward

C) By decreasing the wavelength of seismic waves moving northward and increasing the wavelength of waves moving southward

D) By increasing the wavelength of seismic waves moving northward and decreasing the wavelength of waves moving southward




Im honestly not sure what this ? is asking about. Is there another wave besides the primary rupture? If so, if the wave is moving northward while the primary rupture wave is going northward, wouldnt the frequency detected by the source increase, this the wavelength decreases?

Thanks a lot!!

 

[mitchlucker]

I think the answer would be C based on your reasoning.

"If so, if the wave is moving northward while the primary rupture wave is going northward, wouldnt the frequency detected by the source increase, this the wavelength decreases?"

I'm really not sure what the context is, but based on what is given I'm assuming the "source" is the earthquake and the observer is standing at 74 km north.

There is another "wave" that moves back in the opposite direction. The "observer" at 74 km south would feel the complete opposite effect.