Csmip strong motion data processing
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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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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, Shakal et al


Csmip processing development

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


Uniform processing guiding filter period selection based on signal and noise spectrum trifunac 1977

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


Csmip strong motion data processing

  • 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


Csmip strong motion data processing

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


Steps in processing analog

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


Example whittier analog record

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


Example digitized vol 1

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


Response spectrum

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


Suite of time histories

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


Final accel veloc displ

Final Accel, Veloc, Displ

CSMIP Processing, Shakal et al


Final spectrum

Final Spectrum

  • Filter corners given on plot

  • Plotted only out to corner selected

CSMIP Processing, Shakal et al


Usable data bandwidth

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


Digital records

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


Automatically processed record

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


Csmip strong motion data processing

CISN Internet Quick Report – tied to automatically generated ShakeMap

CSMIP Processing, Shakal et al


Summary 1

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


Summary 2

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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