Dear researchers
How can I determine the predominante frequency of an earthquake from it ground acceleration record using MATLAB.
Best regards.
Dear Mahdi you should do a Fourier analysis or wavelet analysis in order to find the dominate frequencies of earthquake.
Since the earthquake is non resonance signal its frequencies chances during the time so wavelet analysis is better.
I sent you some papers relative to your question
thank you dear Nikos, but is there any MATLAB code for that ?
Regards.
On the other hands, there are other software that can readily perform FFT; such as seismosignal by seismosoft
http://www.seismosoft.com/seismosignal
Dear Mahdi,
I will suggest you to contact Prof. J N Tripathy, Earth and Planetary Science Department, University of Allahabad, India (e-mail : [email protected] ) in this regard. He is expert in the seismological modelling.
Dear Mahdi,
I suggest you read the attached publication, It will be useful.
Good luck.
Je vous propose de lire la publication ci-jointe, elle vous sera utile.
Bon courage.
Dear Mahdi, the previous respondents have not asked you a critical question. Are you looking at "predominant frequency" for the purposes of time history signal content [e.g., FFT] or for engineering or seismic design [e.g., response spectrum]. These are fundamentally different ways at looking at the frequency content associated with earthquake ground motions.
Dear Mahdi, The predominant frequency of a ground motion can be estimated by evaluating the predominant period. This is the period at which the maximum spectral response is observed.
Dear Nikos,
Thanks for providing the reference software for FFT to resolve the signal into magnitudes and corresponding frequencies/periods. By clicking on the link you provided, it requests the application by which one needs to open. Please advise!
Many thanks
Dear Hesham Elshazly the application MATLAB since the files have a ".m" extention.
regards.
Many thanks.
Are there other applications that work automatically online since I do not have MATLAB currently!
Regards,
Dear ALL,
I have another question ,how can the max.frequency from the given acceleration time history data? For the purpose of seismic design.
Sorry
I have another question ,how can choose the max.frequency from the given acceleration time history data? For the purpose of seismic design.
Hesham Elshazly Where is the link to file? I couldn't seem to find it.
Dear Dagnaw,
Actually the maximum frequency in a given record can be irrelevant, where it corresponds to noise. (Recorded frequencies from some source that was working in parallel with the earthquake while measurements were taken).
In fact, frequency is of interest but the maximum amplitude of input force or output response is what concerns us.
For a given application, you need to know beforehand the frequency range (not a maximum frequency), which typically interests you in your application.
The range of frequencies from ground motion, an EQ, may range from 0.5 Hz to 15 HZ, with the range 1.0 to 10 HZ being the most dominant.
What interests one in a given system, with a given relevant frequency range such as 1.0 to 10 HZ in ground motion, is not the maximum frequency but the maximum input force to the structure, like the amplitude of the ground acceleration in this case, or the maximum response of the structure to this input, due to magnification/partial resonance, as reflected in the response spectrum.
The FFT for the input acceleration gives an idea about the share of each frequency in the time history (excitation or response) in general. (Frequency Vs amplitude graph)
If we input the time history of ground motion to a single degree of freedom structure with a given mass and stiffness (frequency/period) and pick up the corresponding maximum response acceleration at that system frequency, we can pick the max acceleration magnitude possible from a system with these properties from the given input excitation.
If we repeat this process for different SDOF frequencies, one at a time, we can build the response spectrum.
In the response spectrum, the relative magnitudes of the maximum accelerations in indicates the level of amplification to the input excitation you can expect if your system contains that frequency.
Hopefully this helps.
Kind regards,
Hesham Elshazly
Dear Bikesh,
You need to perform FFT for the record of the earthquake in your hands.
The frequency/period, at which the amplitude of the FFT is largest, is your predominant frequency.
Kind regards,
Hesham Elshazly
Earthquake signal has several frequency content. At a site a perticular structure has its own natural frequency. At that site first dominant frequency content at which resonance would occur is refered as predominat frequency for that location.
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