1. Norm Abrahamson NGA workshop #5 March 24, 2004
Working Group #1 Report on Evaluation of Data Processing for Response Spectra
Norm Abrahamson
NGA workshop #5
March 24, 2004

2. Issues
PEER data set developed using some different data processing than CSMIP and USGS
Only earthquakes before 1992 are an issue
Are the PEER processed records a valid interpretation of the ground motion (response sepctral values) for use by the NGA developers?
Main Issue
Differences in Filtering

3. Filter Issues Type of filters Selection of corner frequencies
Butterworth vs Ormsby
Causal vs Acausal
Selection of corner frequencies
High-pass corner frequency
Low-pass corner frequency

4. Causal vs Acausal
PEER data base developed using a mixture of casual and acausal filters
Can have significant effect on response spectral values over wide frequency range (not just near the corner frequency)
Largest effect for records with large displacements

5. Causal vs Acausal Conclusion:
Acausal approach preferred (response spectra are less affected by filtering)
On average, there is no systematic difference between response spectra computed using causal and acausal filters
Need to check effect on PGV and PGD.
WG concluded that PEER response spectra are adequate for NGA needs
Will reprocess recordings with large permanent displacement using acausal filters (same records that have fling issue)

6. Filter Corner Frequencies
PEER, CSMIP, USGS use different approaches for selecting the corner frequencies
Selection of corner frequency has large effect on spectral values outside of the pass band.
CSMIP vol II and vol III use different pass bands and time steps

7. Filter Corner Frequencies
Conclusions:
Include both PEER and CSMIP/USGS corner frequencies in the flat file.
Only one set of response spectral values
Developers will select the useable pass band of the spectral values
Duel sets of PGA, PGV and PGD values will be included in flat file (PEER and CSMIP/USGS values
PGV and PGD can be strongly affected by corner frequencies
CSMIP values: April 2
USGS values: ?