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When you perform spectral matching with wavelet model 7, the matching algorithm sometimes needs to add additional points (padding) at the beginning of the record. For bidirectional records, the padding may only be added to one of the components, or the number of padding (added points) for the two components might be different. This results in a shift in the matched record (forward in time).
QuakeManager keeps track of this shift, and allows you to show it or hide it using the options “Shift Padding” & “Show Padding” on the toolbar.
If you perform the spectral matching to the records as components, and then combine them, then there is no guarantee that the padding (number of added points) is the same in both directions.
However, when you run spectral matching on a triplet, then QuakeManager will check the padding in all directions (including vertical if you’re matching vertical) and will ensure that the number of added points is the same in all directions.
To visualize the padding, the user may click on time-histories and under the chart ribbon, the user can use the “Shift Padding” & “Show Padding” buttons on the toolbar (shown below).
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For example, below is a component that was padded by spectral matching.
The following figures are for the same component, plotted using different combinations of the padding options.
First figure shows the actual amount of shift for one component. Here, the padding points (i.e. the added points) are not shown.
Notice how the modified record (in blue) is shifted to the right because of the added padding points.
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Figure: Spectrally matched component where padding is not shifted and not shown
Second image shows the same thing, but with padding points shown (flat zero blue line).
This is a true comparison of how the two records (original and modified) really are. The modified record has additional points added to the beginning because of padding.
While this is what the records look like, it makes it difficult to compare the two, and try to judge how the spectral matching had altered the characteristics of the time history at different times.
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Figure: Spectrally matched component where padding is not shifted but shown
Third image shows the record after QuakeManager shifts the padded (modified) record back in time in order to match the original (visually).
In effect, this subtracts the padding duration from the modified record time series, resulting in some time values being negative.
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Figure: Spectrally matched component where padding is shifted and shown
In the fourth figure, we turn off “Show Padding”, and now the padding (negative time) is hidden, and only positive time is shown.
In this case, the original and matched records appear synchronized as you might expect them, which allows you to compare the characteristics of the original and modified histories at each time step.
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Figure: Spectrally matched component where padding is shifted but not shown
The final figure show both components (H1 & H2) and shows how both modified/matched components are equally shifted relative to the original components.
When you perform bidirectional spectral matching, QuakeManager ensures that the amount of padding is the same for both components.
This ensures that the two components can be used in a bidirectional analysis and that they will be consistent and “in-phase”.
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Figure: Spectrally matched components where padding is not shifted and not shown
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