Good morning,
I'd like to know if is possible to obtain a Fourier Spectrum from an accelerogram with your software.
I have started using Seismosoft since last week so I have not so much confidence with it (and actually with time history analysis in general), but I don't understand why my Fourier Spectra have some peaks at a frequencies that seem to be more or less 1/DT where DT is the accelerogram time step.
I thank you in advance for your explanations,
Regards,
Angelo Farnetano
Fourier Spectrum and accelerogram
 seismosoft
 Posts: 1222
 Joined: 06 Jul 2007, 04:55
Re: Fourier Spectrum and accelerogram
Yes, it is possible to create the Fourier Spectrum with SeismoSignal. The spectrum is automatically calculated and displayed in the "Fourier and Power Spectra" page.
Seismosoft Support
Seismosoft Support

 Posts: 2
 Joined: 24 May 2017, 10:52
Re: Fourier Spectrum and accelerogram
Is it possible the reverse operation? I mean to obtain an accelerogram from a Fourier spectrum.
Regards
Angelo
Regards
Angelo
 seismosoft
 Posts: 1222
 Joined: 06 Jul 2007, 04:55
Re: Fourier Spectrum and accelerogram
No, it is not possible to create an accelerogram from the Fourier spectrum.
However, you can create artificial or generated records that match response spectra given by the user with SeismoMatch and SeismoArtif.
Seismosoft Support
However, you can create artificial or generated records that match response spectra given by the user with SeismoMatch and SeismoArtif.
Seismosoft Support
Re: Fourier Spectrum and accelerogram
I'll add that SeismoArtif performs spectral matching in the frequency domain (using Fourier analysis), while SeismoMatch performs spectral matching in the time domain (using wavelets). So, while you cannot explicitly define the Fourier spectrum in SeismoArtif, if you can come up with an acceleration response spectrum which transforms to your Fourier spectrum, you could essentially do what you wish (I believe). I am certainly no expert on Fourier transforms and Inverse transforms, but it does seem possible with some external manipulation and development of the target acceleration spectrum.
Tim Huff
Re: Fourier Spectrum and accelerogram
What is the meaning of the nonzero power amplitude and Fourier amplitude at zero frequency when truncating an earthquake acceleration record? It is of appreciation if you could demystify the rationale behind the aforesaid nonzero values plus the way which otta be utilized to set them back to zero.
Thanks a ton!
Navid
Thanks a ton!
Navid
 seismosoft
 Posts: 1222
 Joined: 06 Jul 2007, 04:55
Re: Fourier Spectrum and accelerogram
The value of the frequency is close to zero but not zero. You will notice this in the corresponding table on the left of the plot.
Regards,
Seismosoft Support
Regards,
Seismosoft Support

 Posts: 12
 Joined: 23 Jun 2023, 08:51
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Re: Fourier Spectrum and accelerogram
Hello Angelo Farnetano,
It's great to hear that you've started using Seismosoft for your analysis. I can help clarify some issues you're encountering with your Fourier Spectrum from the accelerogram.
The Fourier Spectrum is a plot that shows the amplitudes of various frequency components present in a timedomain signal, in your case, an accelerogram. It's commonly used in earthquake engineering and structural analysis to understand the frequency content of ground motion.
Regarding your observation of peaks at frequencies around 1/DT, it's not uncommon to see such peaks in the Fourier Spectrum when working with discretetime signals like accelerograms. Here's why:
Sampling Theorem: The NyquistShannon sampling theorem states that to accurately represent a signal in the frequency domain, you need to sample it at a rate that is at least twice the highest frequency present in the signal. If your accelerogram was not sampled at a rate significantly higher than the highest frequency content of the ground motion, you might see aliasing effects in the Fourier Spectrum.
I hope this helps you better understand the peaks in your Fourier Spectrum. If you have further questions or need more clarification, feel free to ask.
Best regards,
[Jatin Gupta]
It's great to hear that you've started using Seismosoft for your analysis. I can help clarify some issues you're encountering with your Fourier Spectrum from the accelerogram.
The Fourier Spectrum is a plot that shows the amplitudes of various frequency components present in a timedomain signal, in your case, an accelerogram. It's commonly used in earthquake engineering and structural analysis to understand the frequency content of ground motion.
Regarding your observation of peaks at frequencies around 1/DT, it's not uncommon to see such peaks in the Fourier Spectrum when working with discretetime signals like accelerograms. Here's why:
Sampling Theorem: The NyquistShannon sampling theorem states that to accurately represent a signal in the frequency domain, you need to sample it at a rate that is at least twice the highest frequency present in the signal. If your accelerogram was not sampled at a rate significantly higher than the highest frequency content of the ground motion, you might see aliasing effects in the Fourier Spectrum.
I hope this helps you better understand the peaks in your Fourier Spectrum. If you have further questions or need more clarification, feel free to ask.
Best regards,
[Jatin Gupta]