Effects of Digital Filtering in Data Processing of Seismic Acceleration Records
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Research Article Effects of Digital Filtering in Data Processing of Seismic Acceleration Records Guergana Mollova Department of Computer-Aided Engineering, University of Architecture, Civil Engineering and Geodesy, 1046 Sofia, Bulgaria Received 12 April 2006; Revised 8 August 2006; Accepted 24 November 2006 Recommended by Liang-Gee Chen The paper presents an application of digital filtering in data processing of acceleration records from earthquakes. Butterworth, Chebyshev, and Bessel filters with different orders are considered to eliminate the frequency noise. A dataset under investigation includes accelerograms from three stations, located in Turkey (Dinar, Izmit, Kusadasi), all working with an analogue type of seismograph SMA-1. Records from near-source stations to the earthquakes (i.e., with a distance to the epicenter less than 20 km) with different moment magnitudes Mw = 3.8, 6.4, and 7.4 have been examined. We have evaluated the influence of the type of digital filter on time series (acceleration, velocity, displacement), on some strong motion parameters (PGA, PGV, PGD, etc.), and on the FAS (Fourier amplitude spectrum) of acceleration. Several 5%-damped displacement response spectra applying examined filtering techniques with different filter orders have been shown. SeismoSignal software tool has been used during the examples. Copyright © 2007 Hindawi Publishing Corporation. All rights reserved.
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INTRODUCTION
This material presents a study on the influence of signal processing techniques (digital filtering) used in data processing of acceleration records from earthquakes. The recorded raw ground motion signals are always preprocessed by seismologists before any engineering and seismological analysis takes place. Strong-motion data processing has two main objectives to make the data useful for engineering analysis: (1) correction for the response of strongmotion instrument itself (analogue or digital type of instrument can be used) and (2) reduction of random noise in the recorded signals [1]. Different authors and agencies around the world use various steps in data processing. The major three organizations in the United States (USGS, PEER, CSMIP) (USGS (US Geological Survey), PEER (Pacific Earthquake Engineering Research Centre), CSMIP (California Strong-Motion Instrumentation Program)) also use different signal processing techniques to process records. For example, CSMIP realizes several basic steps [2]: (i) baseline correction (described in Section 2), (ii) instrument correction, (iii) high-frequency filtering (Ormsby filter or lowpass Butterworth with 3rd-/4th-order for digital records), (iv) computation of response spectra (for damping values of 0, 2, 5, 10, and 20% of critical), and (v) high-pass filtering (the most important issue here is the choice of filter corner).
Another investigation is done in the frame of Italian Network ENEA [3]. A comparison between corrected acceleration for Campano-Lucano earthquake (Italy, 23/11/1980) using time-domain FIR (Ormsby filter), IIR (elliptic filter), and fre
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