HR: 0800h
AN: S31B-1050    [Abstracts]
TI: Filtering Applications on Seismogram Analysis
AU: * Djordjevic, M
EM: marija.djordjevic@mail.uh.edu
AF: University of Houston, 4800 Calhoun Rd, SR1,RM312, Houston, TX 77204 United States
AB: Useful data extraction from registered signals is an everyday problem. Seismogram filtering can be used to enhance the earthquake signal, especially, knowing that period range is strongly amplified by the seismograph itself. The goal of this project was to estimate tradeoffs between noise reduction and the sharpness of the filtered earthquake signal. The different filter bands were applied on the seismograms from different epicentral distances, including both local and regional earthquakes, in order to see the quality of the data. During the seismogram analysis we had two approaches: reading the wave phase (arrival time, amplitude, period) and spectral analysis, since frequency filtering is essential. The well-known set of Fourier orthogonal basis functions was used for spectral analysis. The main purpose of filtering was to remove the noise from the seismograms and to get as much possible information from the record. Practical application was obtained using custom made "Analysis" software. We processed 5 earthquake signals; four local and one distant earthquake. The data came from Djerdap Seismological Station, Serbia. Filtering was based on a band-pass filter with frequency cut-offs from 0.2Hz to 10Hz. Every record was filtered with five filters (10-1Hz,10-2.5Hz, 2.5-1Hz, 1-0.2Hz). The manipulation with different filter bands allowed us to define precisely the beginning of the earthquakes and first arrivals of different wave phases. The best result for the 45km epicentral distance earthquake was obtained using window 0.1-0.5sec, where very clear Pg and Sg arrivals could be distinguished. The distant earthquake showed the advantages of filtering seismograms to enhance the long period energy. The lowest frequency band-pass filter (1-0.2Hz) was the most successful. The results of the experiment were with very clear Pg and Sg arrivals when the right bands were used for filtering. This improved the quality of the original signals by emphasizing the temporal and frequency characteristics of interest.
DE: 7299 General or miscellaneous
DE: 7200 SEISMOLOGY
DE: 7215 Earthquake parameters
SC: Seismology [S]
MN: 2004 AGU Fall Meeting