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COSMOS INVITED WORKSHOP ON STRONG-MOTION RECORD PROCESSING May 26-27, 2004, Oakland, CA

COSMOS INVITED WORKSHOP ON STRONG-MOTION RECORD PROCESSING May 26-27, 2004, Oakland, CA. Processing of European Strong-Motion Records at Imperial College London. Julian J. Bommer & John Douglas. Imperial College London does not operate strong-motion networks,.

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COSMOS INVITED WORKSHOP ON STRONG-MOTION RECORD PROCESSING May 26-27, 2004, Oakland, CA

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  1. COSMOS INVITED WORKSHOP ON STRONG-MOTION RECORD PROCESSING May 26-27, 2004, Oakland, CA Processing of European Strong-Motion Records at Imperial College London Julian J. Bommer & John Douglas

  2. Imperial College London does not operate strong-motion networks, operates as a data collection and dissemination center for accelerograms recorded in Europe, the Middle East and the Mahgreb Data supplied by a large number of agencies using many different instruments and digitization procedures

  3. Non-Standard Errors ~50% of the 3,000 European accelerograms affected • Insufficient sampling rate • Zero or negative time steps • Poor digitizer resolution (analog) • S-wave triggers • Spurious spikes • Multiple baselines • Poor digitizer resolution (digital)

  4. Multiple Digitizations

  5. Digitization of Analog Recordings

  6. Low-Resolution Digital Recordings

  7. Ratios of Simulated to True Spectral Acceleration Peak Ground Acceleration (m/s2) T = 0.2 s T = 2.0 s

  8. Instrument Corrections Not applied for a large proportion of the databank because transducer frequency and damping not known • Is the correction important for, say, SMA-1 records? • Does the correction amplify high-frequency noise? • At what frequency is spectral acceleration equal to PGA?

  9. Filtering, Long-Period Ordinates and PGD The importance of the high-pass filter increased significantly when our studies focused on peak ground velocity (PGV) and displacement (PGD), and response spectra of displacement Issues for filtering analog records: • How to select low-frequency cut-off? • Can it be higher than the corner frequency? • Same cut-off for all three components? • Ratio of usable to cut-off periods? • Longest period ordinates from analog records?

  10. Sensitivity to Long-Period Filter Cut-Off

  11. Sensitivity to Long-Period Filter Cut-Off

  12. Baseline only CD-ROM vol. 2 CD-ROM vol. 1 ISESD web site Bommer & Elnashai (1999)

  13. Cut-off from FAS of fixed trace

  14. Cut-off from FAS of pre-event memory

  15. Cut-off from shape of FAS of (strong) record

  16. Cut-off from shape of FAS of (weak) record

  17. High-Pass Filter Cut-Off Berge-Thierry et al. (2003) - Ms 7.5, Rock Site at 10 km

  18. Courtesy of D.M. Boore

  19. NEHRP 2003 Period defining constant displacement plateau

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