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UNIVERSITY OF BUCHAREST
FACULTY OF PHYSICS Guest
2024-11-22 2:06 |
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Conference: Bucharest University Faculty of Physics 2005 Meeting
Section: Atmosphere and Earth Science; Environment Protection
Title:
Variations in the microseismic noise level observed at the Bucovina Seismic Array (BURAR)
Authors:
Daniela Ghica(1), Mircea Radulian(1) and Mihaela Popa(1)
Affiliation:
National Institute for Earth Physics, 12 Calugareni St., 077125, PO Box MG-2 Magurele, Romania, Tel.: +4021 493 01 17
E-mail
daniela@infp.ro
Keywords:
Abstract:
The microseismic noise level analysis for a seismic array is an essential step to accurately process the data recorded by the system. Basically, the observed background noise is a complex combination of natural and cultural sources as local geology, specific area activity (roads traffic, agricultural and industrial activities) or weather conditions.The understanding of the BURAR site noise characteristics is important for the array specific techniques (beamforming, f-k analysis), to apply the correct bandpass filtering, in order to obtain noise suppression and conservation of the `true` seismic signal. The array monitoring potential of very small earthquakes and explosions will be enhanced, based on the best signal-to-noise ratio.The noise study at BURAR was carried out over one-year period, considering the noise power spectra in a 0.1 to 10 Hz frequency interval, for every 24 hours: 5 minutes during day and 5 minutes during night. Only short-period vertical sensors were considered. Systematic variations in the microseismic noise level at the BURAR site were observed:- diurnal: a decreasing of about 40% in night noise level at 1 Hz frequency; at 6 Hz frequency, the decreasing could reach 80-90% for `non-winter` months (May to October);- seasonal: during the winter time, a lower noise level is underlined, due to the restraining of the local specific activity (especially agriculture and farming) and of the road traffic.To summarize the level of microseismic noise observed at BURAR for one-year observations, a model curve for array noise level has been estimated, including upper and lower bounds of noise power density together with average spectrum. The BURAR noise model will be useful in the process of local site conditions estimation, by eliminating the noise contribution from the array recording. Also, the detection processing, phase identification and events location procedures will be significantly improved.
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