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Earthquake body wave frequency and the Richter Scale

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A young person from India asks, "i have made a home made seisemoscope but do not know how to represent the frequency on richter scale help"  The Richter Scale is usually defined in terms of wave amplitude. Perhaps we could extend the question to a discussion about any connection between earthquake body wave frequency and seismographs as it might relate to the Richter Scale.

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rfrench1
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Cidade Universitária Ilha do Fundão, Rio de Janeiro, 巴西
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Tom

I saw that this question was submitted some time ago, with no response yet, so here are some ideas:

I suspect this may be a case of slight misunderstanding of terminology, and that the questioner may in fact be asking for how to represent the magnitude on the Richter scale, since this is the property which the scale indicates.

It will probably be fairly difficult to accurately and consistently calculate a reliable Richter value from a home-made seismograph, since seismographs in use for research purposes are engineered to very precise tolerances and conform to a rigourous standards.  Networks of seismographs will be used to enable some statistical validity and error-correction to be applied to the observed results, and to enable some understanding of the spatial variation in the effects of the earthquake energy as it propogates.

With the home-made seismograph, there will be a number of factors which will introduce noise (unwanted distortion) into the measurement which will be a function of the instrument’s construction.

I think a practical way to use the home-made unit would be primarily to look at the recorded data to understand the onset and passage of the seismic event in terms of its characteristics in a more qualitative way, and how these relate to ground movement in general.  It may be possible, by recording a number of events and then comparing the displacements seen from the home-made unit to official magnitudes documented on publically-available earthquake websites for the same events, to loosely calibrate the home-made unit, but I wouldn’t guarantee the consistency of the results, as the magnitude is also a function of distance for the origination of the seismic event. 

Usually, on the public websites, you can select an event and click on a link to bring up a seismogram from the unit/network used.  It could be interesting to do that and compare the result there with the home-made unit, and then think about what factors could contribute to the differences seen, whether, how and how much we can compensate for them.  This could be an interesting starting point for thinking about measurement, accuracy, noise, statistics and probably quite a few other topics.

If indeed the questioner is trying to extract some frequency information, then I think they will have to be prepared to either construct quite a sophisticated seismograph, or be prepared to do some observation from the recorded data and visually extract information with which to derive some simplified frequency content / characteristics evident (and continuously varying) over time as a given event is observed. 

The waveform we see on a seismogram is the result of complex series of physical interactions within the earth, (and also, to an extent, a function influenced by the characteristics of the sensor and recording equipment, but we try to minimize that effect), so the frequency content will be complicated also.

Regards

Richard