Surface waves modes help

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bididi
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Joined: Fri Mar 27, 2020 6:27 pm

Surface waves modes help

Post by bididi »

Hi, i am studying applied Geophysics and Seismology. I am really trying to understand what a fundamental and a higher mode is, when we refer to Surface waves. Can someone explain to me in plain terms,what does they mean? Thanks for your time!!
John :D

Alejandro
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Re: Surface waves modes help

Post by Alejandro »

This is what I understand about it
An object (string, particle, etc..) can only vibrate in a stable and sustained way (periodic wave) only at certain excitation frequencies. The lowest of these frequencies is known as the fundamental frequency (or fundamental mode). This is, the lowest frequency that can generate a stable oscillation on that object. There are more frequencies, higher than the fundamental frequency, at which this object can vibrate in a stable way, these are known as the higher modes or harmonics. The most general motion of a system is a superposition of its normal modes.
This applied to seismic waves, it's only the oscillation frequencies that are observed in these waves. In an f-k graph, applying the MASW technique for example, sometimes you can see some of the harmonics of the rayleigh waves that are scattered through the medium.

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