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

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

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

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

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)

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

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: ?