New Seismic Noise Models Obtained Using Very Broadband Stations
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Pure and Applied Geophysics
New Seismic Noise Models Obtained Using Very Broadband Stations ABD
EL-AZIZ
KHAIRY ABD
EL-AAL
Abstract—It has been two decades since the last comprehensive standard model of ambient earth noise was published Peterson (Observations and modelling of seismic background noise, US Geological Survey, open-file report 93–322, 1993). The PETERSON model was updated by analyzing the absolute quietest conditions for stations within the GSN (BERGER et al. in J Geophys Res 109, 2005; MCNAMARA and BULAND in Bull Seism Soc Am 94:1517–1527, 2004; RINGLER et al. in Seismol Res Lett 81(4) doi: 10.1785/gssrl.81.4.605, 2010). Unfortunately, both the original model and the updated models did not include any deployed station in North Africa and Middle East, which reflects the noise levels within the desert environment of those regions. In this study, a survey was conducted to create a new seismic noise model from very broadband stations which recently deployed in North Africa. For this purpose, 1 year of continuous recording of seismic noise data of the Egyptian National Seismic Network (ENSN) was analyzed in order to create a new noise model. Seasonal and diurnal variations in noise spectra were recorded at each station. Moreover, we constructed a new noise model for each individual station. Finally, we obtained a new cumulative noise model for all the stations. We compared the new high-noise model (EHNM) and new low-noise model (ELNM) with both the high-noise model (NHNM) and low-noise model (NLNM) of PETERSON (Observations and modelling of seismic background noise, US Geological Survey, open-file report 93–322, 1993). The obtained noise levels are considerably lower than low-noise model of PETERSON (Observations and modelling of seismic background noise, US Geological Survey, open-file report 93–322, 1993) at ultra long period band (ULP band), but they are still below the high-noise model of PETERSON (Observations and modelling of seismic background noise, US Geological Survey, open-file report 93–322, 1993). The results of this study could be considered as a first step to create permanent seismic noise models for North Africa and Middle East regions. Key words: Ambient earth noise, Egyptian National Seismic Network (ENSN), high-noise model (NHNM).
1. Introduction Since the original noise model of PETERSON (1993) and its update do not have any information about
1 Seismology Department, National Research Institute of Astronomy and Geophysics, Helwan, Cairo, Egypt. E-mail: [email protected]
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and MAHMOUD SAMI SOLIMAN1 noise level in North Africa, Middle East and Arab world where PETERSON (1993) stated in his publication pages 1 and 31 ‘‘one might hope for a better distribution of stations in southern hemisphere, especially Africa, and south America in order to look for regional variations in seismic noise’’. He also pointed that ‘‘the new low-noise model NlNM may also need revision if data records from mid-continent sites are found’’ and while the observations of ambient earth noise from the recently
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