Wyniki wyszukiwania - BazTech

1

Analysis of the primary and secondary microseisms in the wavefield of the ambient noise recorded in northern Poland

Lepore S., Grad M.

Acta Geophysica

|

2018

|

Vol. 66, no. 5

915--929

EN

Seasonal changes of the primary and secondary microseisms were analysed in the wavefield of the ambient noise recorded during the entire 2014 at the ‘‘13 BB star’’ array located in northern Poland, composed of thirteen, symmetrically arranged, broadband seismic stations. To that, spectral analysis, seismic interferometry, surface scalar wind speed distribution, and beamforming were used. Spectral analysis allowed to observe that a splitting of the secondary microseism peak was present in winter and autumn, and that the primary microseism peak was visible in spring, summer and autumn. Using seismic interferometry, the long-term characteristics of the noise wavefield were recognized. The seasonal variations of the secondary microseism source were described by means of the analysis of the surface scalar wind speed for each month. The splitting of the secondary peak was attributed to the interaction of a strong wind blowing from the North Sea with a weak wind blowing from the Baltic Sea. The seasonal variations of the primary microseism peak were characterized through the frequency-domain beamforming. The peak was identified during spring, summer and autumn, when the generated wavefield was coming from the Baltic Sea. The velocity of the wavefield was evaluated within the 2.0–5.0 km/s range. The described mechanism of generation of the microseisms, based on the interaction of the nearby winds, was found to be consistent with the models reported in the literature.

2

Signal conditioning for examination of shallow-water acoustic noise correlation properties

Rudnicki M., Marszal J.

Hydroacoustics

|

2016

|

Vol. 19

335--340

EN

The article describes the process of signal conditioning for examination of acoustic noise correlation properties in shallow water. Knowledge of these properties is very important for the design processes of passive and active hydroacoustic systems. This paper focuses on the above issue from the point of view of passive sonar. In sonar systems, signal processing algorithms operate on both useful acoustic signals, and accompanying noise. Quantitative estimation of the correlation properties of acoustic noise enables an accurate determination of detection conditions. This will verify the validity of certain commonly used simplified models in simulations of hydroacoustic systems. The article presents how the measurement system was constructed, and the structure of files for storing measurement data. It describes the processing algorithm developed for the measured signal conditioning. Research results are presented and discussed.

3

Lithospheric structure of the Arabian Shield from joint inversion of P- and S-wave receiver functions and dispersion velocities

Al-Amri A. M.

Acta Geologica Polonica

|

2015

|

Vol. 65, no. 2

227--243

EN

New velocity models of lithospheric thickness and velocity structure have been developed for the Arabian Shield by three tasks: 1) Computing P-Wave Receiver Functions (PRFs) and S-Wave Receiver Functions (SRFs) for all the broadband stations within the Saudi seismic networks. The number of receiver function waveforms depends on the recording time window and quality of the broadband station. 2) Computing ambient noise correlation Green’s functions for all available station pairs within the Saudi seismic networks to image the shear velocity in the crust and uppermost mantle beneath the Arabian Peninsula. Together they provided hundreds of additional, unique paths exclusively sampling the region of interest. Both phase and group velocities for all the resulting empirical Green’s functions have been measured and to be used in the joint inversion. 3) Jointly inverted the PRFs and SRFs obtained in task 1 with dispersion velocities measured on the Green’s functions obtained in task 2 and with fundamental-mode, Rayleigh-wave, group and phase velocities borrowed from the tomographic studies to precisely determine 1D crustal velocity structure and upper mantle. The analysis of the PRFs revealed values of 25 - 45 km for crustal thickness, with the thin crust next to the Red Sea and Gulf of Aqaba and the thicker crust under the platform, and Vp/Vs ratios in the 1.70 – 1.80 range, suggesting a range of compositions (felsic to mafic) for the shield’s crust. The migrated SRFs suggest lithospheric thicknesses in the 80-100 km range for portions of the shield close to the Red Sea and Gulf of Aqaba and near the Arabian Gulf. Generally, the novelty of the velocity models developed under this paper has consisted in the addition of SRF data to extend the velocity models down to lithospheric and sub-lithospheric depths.

4

Discrimination between stochastic dynamics patterns of ambient noises (Case study for Oni seismic station)

Matcharashvili T., Chelidze T., Javakhishvili Z., Zhukova N., Jorjiashvili N., Shengelia I.

Acta Geophysica

|

2013

|

Vol. 61, no. 6

1659--1676

EN

Investigation of complex dynamics of ambient seismic noise remains as an important scientific research challenge. In this work we investigated dynamical features of the ambient noises at Oni seismic station, Georgia. We used stochastic model reconstruction method from measured data sets. Seismic records for different time periods around Oni seismic station have been analysed. It was shown that the dynamics of fluctuations of seismic noise vertical component undergoes essential changes for considered time period from 2005 to 2012. These changes are more noticeable for time periods of preparation and aftershock activity of strong M6.0 earthquake occurred in 2009 in the vicinity of Oni seismic station.

5

Scaling features of ambient noise at different levels of local seismic activity. A case study for the Oni seismic station

Matcharashvili T., Chelidze T., Javakhishvili Z., Zhukova N.

Acta Geophysica

|

2012

|

Vol. 60, no. 3

809-832

EN

Investigation of dynamical features of ambient seismic noise is one of the important scientific and practical research challenges. We investigated scaling features of the ambient noises at the Oni seismic station, Georgia, using detrended fluctuation analysis method. Data from this seismic station, located in the epicentral zone of Oni M6.0, 2009, earthquake, were selected to include time periods with different levels of local seismic activity. It was shown that the investigated ambient noise is persistent longrange correlated at calm seismic conditions in the absence of earthquakes. Fluctuation features of the analyzed ambient noises were affected by local earthquakes, while remote seismic activity caused just slight quantitative changes. Processes related to the preparation of a strong local earthquake may cause quantifiable changes in fluctuation features of ambient noises. Fluctuation features of seismic noise for periods of increased local seismic activity cease to be long-range correlated and appear to become a complicated mixture of random and correlated behaviours.

6

Hałas w otoczeniu mostów blachownicowych

Stojek Z., Janas L., Łakota W.

Zeszyty Naukowe Politechniki Rzeszowskiej. Mechanika

|

1999

|

z. 52 [174]

463-474

EN

In the presented paper, the acoustic effects in the vicinity of railway bridges have been studied. The results of experimental research of steel, girder railway bridge noise are presented. The loudness level and vibrations diagrams depending on corresponding frequency has been given.