PEER Strong Motion Database
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Strong motion data processing has two major objectives to make the data useful for engineering analysis: (1) correction for the response of the strong motion instrument itself, and (2) reduction of random noise in the recorded signals. The processing concentrates on extending both the high- and low-frequency ranges of the useable signal in the records. More recent data, particularly from digital recorders, do not benefit from additional processing and are entered unaltered into the database after review.
To achieve these objectives, the flowchart identifies the important steps in the processing of records in the PEER Strong Motion Database. The processing begins with Volume 1 or 2 data from the strong motion data provider. In some cases, only film records (such as SMA-1) are available so a digitizing step is necessary, which introduces considerable noise over a wide frequency range.
The instrument response is deconvolved in the Fourier domain accounting for the amplitude and phase of the instrument. Noise is reduced through the use of causal Butterworth filters at both high- and low-pass frequencies to produce a frequency range over which the earthquake ground motion in the recorded signal significantly exceeds the noise level. The LP and HP filter frequencies are selected individually for each component of a record based on an assessment of the Fourier amplitude spectrum and the integrated displacement time history D(t).
Since the Butterworth filter has a significant reduction (0.707) at the LP and HP frequencies, the useable bandwidth of the records for the purpose of engineering analysis is within 1/1.25 of the LP frequency and and 1.25 of the HP frequency.
The processing of the strong motion records in the PEER database is in general different than the processing done by the agency that collected the data. Although the processed records may be different, the differences should be small within the frequency passband common to both processing procedures.