Waterfall SRS, 1940 El Centro Quake



The top figure is the time history from the El Centro earthquake, North-South horizontal component.  The second is the corresponding Waterfall FFT with 4 second segments and with 50% overlap.

The Waterfall FFT is calculated by first taking the complete response time history for each natural frequency of interest.  Then the time history for each is divided into segments.  Finally, the shock response spectrum (SRS) is taken for each natural frequency and for each segment, by taking the peak positive and peak negative responses.

The Waterfall SRS function is given in:

Matlab script: Vibrationdata Signal Analysis Package

>> vibrationdata > Time History > Shock Response Spectrum, Various > Waterfall FFT

See also:  El Centro Earthquake

– Tom Irvine

IEEE Std 693-2005, Recommended Practice for Seismic Design of Substations

I am currently researching IEEE Std 693…

One of its recommended shaker test methods for power equipment is to use a “sine beat” acceleration time history. The main frequency is selected as the equipment’s natural frequency.

The minimum number of beats is 5 with a minimum of 10 cycles within each beat pulse. There is also a pause between beat pulses.

A problem with this approach is that the corresponding displacement has a stair-step effect for a whole number of cycles. This offset disappears if an extra half-cycle is added. An example would be to use 10.5 cycles.

Here is a slide presentation:  IEEE_693_sine_beat.pptx

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I have added a function for generating IEEE sine beat time histories to the Vibrationdata GUI package.

Matlab script: Vibrationdata Signal Analysis Package

>> vibrationdata > Miscellaneous > Generate Signal > IEEE std 693 Sine Beat

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The package also has a function for generating the Required Shock Spectrum (RSS) levels.

>> vibrationdata > Import Data to Matlab > SRS Library Array > IEEE std 693 RSS, Various

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An Implementation of an Earthquake Test, According to the Sine-Beat Method: Sine_beat.pdf

Seismic Considerations of Circuit Breakers: Seismic_Considerations_of_Circuit_Breakers.pdf

IEEE 693 Seismic Qualificaiton of Composites for Substation High-Voltage Equipment: 13_2306.pdf 

– Tom Irvine

Webinar 19 – Digital Filtering

PowerPoint File:


Audio/Visual File:

NESC Academy Digital Filtering – Recommend viewing in Firefox with Sliverlight plugin

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Python version:


Python script: Python Signal Analysis Package GUI

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Data:  sm.txt     –  unscaled relative displacement vs. time (sec)

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Reference Paper:

An Introduction to the Filtering of Digital Signals:  filter.pdf

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Matlab script: Vibrationdata Signal Analysis Package

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See also:

Vibrationdata Webinars

USGS, Solomon Island Earthquake, October 8, 2004

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If you would like to be included on the distribution list for the Webinar series, please send an Email to: tom@irvinemail.org

Thank you,
Tom Irvine

Vibrationdata Newsletter March 2012

I posted a newsletter at:


The topics are:

James Webb Space Telescope Isolation
The Prandtl-Glauert Singularity
Seneca Guns
Loudest Stadium Crowd

Please also see my profile at:


Tom Irvine

Vibrationdata Newsletter

I have posted the January 2012 Newsletter at:


The topics are:

Slow Earthquakes
Rumbler Siren
Shepard Tones
Toadfish Mating Call

There are seven accompanying sound files and one Matlab script.

Please let me know if you have any questions.

Thank you,
Tom Irvine