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CSMIP Strong Motion Data Processing

CSMIP Strong Motion Data Processing. Anthony Shakal, Moh Huang and Vladimir Graizer California Strong Motion Instrumentation Program California Geological Survey (was CDMG) Sacramento, California. CSMIP Processing Development.

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CSMIP Strong Motion Data Processing

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  1. CSMIP Strong Motion Data Processing Anthony Shakal, Moh Huang and Vladimir Graizer California Strong Motion Instrumentation Program California Geological Survey (was CDMG) Sacramento, California CSMIP Processing, Shakal et al

  2. CSMIP Processing Development • CSMIP began joint processing project with USGS in late ‘70s (film scanning by Towill Co.- software devel. and processing at Lawrence Berkeley Lab) • In early ‘80s standalone processing at CSMIP • Scanning system installed patterned after that developed at Univ. Southern Calif. by Trifunac & Lee • Processing software of Caltech Bluebook project (Hudson et al) as modified by Trifunac & Lee • Software upgraded for production, with noise level improvement at CSMIP CSMIP Processing, Shakal et al

  3. Uniform Processing – Guiding filter period selection based on Signal and Noise Spectrum (Trifunac, 1977) Digitized accelerogram as sum of desired acceleration and background noise CSMIP Processing, Shakal et al

  4. Signal spectrum moves up and to the right with increasing magnitude • Noise spectrum controlled by • digitization (by film scanner, or by A-to-D converter) • sensor properties • Initial filter corner estimate - above & left of junction, an SNR 2 or 3 • Final corner guided by time domain output of suite of runs having filter near this period CSMIP Processing, Shakal et al

  5. Current CSMIP procedure is to use one filter corner for all components • Pro: Multi-dimensional aspects can be studied by end user • Particle motion • Torsional response in structures • Con: Period controlled by the lowest signal/highest noise channel (often vertical, or lowest n building) CSMIP Processing, Shakal et al

  6. Steps in processing (analog) • Baseline correction – minimal (remove mean; perhaps remove slope) • Instrument correction • High-frequency filtering (25 Hz Ormsby classically) • Initial integration & long period filtering • Maximum-bandwidth response spectra • Time-history suite for long-period filter selection • Final product preparation CSMIP Processing, Shakal et al

  7. Example – Whittier analog record • Digitize at 200 points/cm • Digitize two fixed traces for reference-trace subtraction to remove film shift (earthquake) and film drift (canister) problems • Use 2 pulse/sec time trace to correct film-speed change errors • Digitize fiducial marks placed on film to control multiple-panel concatenation CSMIP Processing, Shakal et al

  8. Example – Digitized (Vol. 1) • Digitized, time-corrected, 200 pts/sec, scaled by sensitivity • Match-test to film image, check for offsets, drifts, panel-junction effects CSMIP Processing, Shakal et al

  9. Response Spectrum • Response spectrum (Nigam-Jennings) of Vol.1 data • ‘Wide-open’ bandwidth • Compare the long period decay of signal spectrum with long-period noise • Initial corner estimate CSMIP Processing, Shakal et al

  10. Suite of time-histories • Range of corners from 12 second to 2.5 sec period • Period chosen was 3.5 second CSMIP Processing, Shakal et al

  11. Final Accel, Veloc, Displ CSMIP Processing, Shakal et al

  12. Final Spectrum • Filter corners given on plot • Plotted only out to corner selected CSMIP Processing, Shakal et al

  13. Usable Data Bandwidth • 3 dB (half-power) points (whether Ormsby, Butterworth or other filter) define UDB for user • User assumed to be knowledgeable, but not necessarily in data processing CSMIP Processing, Shakal et al

  14. Digital Records • Frequency domain processing • Noise level controlled by A-to-D converter’s effective number of bits (last bits often noise) • In general, more dynamic range (72, 96 dB, or more vs ~50-60 dB) • Sensor noise/drift more critical – the next focus in getting the most from recorded data CSMIP Processing, Shakal et al

  15. Automatically Processed Record Record processed automatically at the time of the earthquake (2 am Sunday morning, May 9, M4.4 off Santa Barbara). CSMIP Processing, Shakal et al

  16. CISN Internet Quick Report – tied to automatically generated ShakeMap CSMIP Processing, Shakal et al

  17. Summary (1) • CSMIP processing evolved from the Caltech Bluebook project as extended at USC • Nearly 1000 records digitized/processed (1000s of traces) • General approach goal is to release as much signal as possible, with as little noise accompanying the signal as practical • Using one filter corner per record means that results may be: • more conservative than another policy would yield; but • less difficult to use, for most users CSMIP Processing, Shakal et al

  18. Summary (2) • No acausal filters routinely used; processing of special problem or offset records done by hand, on case-by-case basis, or restricted band pass provided • Automatic processing done by straightforward processing, with diagnostic checks/set-asides if potential problems (DC shifts, electronic noise events, etc) • Automated processing and Internet Quick Report providing rapid release for response and post-earthquake engineering evaluations. CSMIP Processing, Shakal et al

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