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Working Group #1 Report on Evaluation of Data Processing for Response Spectra

This report evaluates the data processing methods used for response spectra in the context of the NGA workshop. The main focus is on the differences in filtering approaches, particularly the choice between causal and acausal filters. The conclusions highlight the preference for using acausal filters and suggest reprocessing recordings with large permanent displacement. Additionally, the report addresses the selection of filter corner frequencies and their impact on spectral values. Recommendations are made regarding including both PEER and CSMIP/USGS corner frequencies in the flat file and including dual sets of PGA, PGV, and PGD values.

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Working Group #1 Report on Evaluation of Data Processing for Response Spectra

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  1. 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 • 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: ?

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