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UNIVERSITY OF BUCHAREST
FACULTY OF PHYSICS Guest
2024-11-23 2:37 |
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Conference: Bucharest University Faculty of Physics 2023 Meeting
Section: Atmosphere and Earth Science; Environment Protection
Title:
On near-surface site characterization surveys performed with the Atom 3C seismographs using seismic methods
Authors:
Andreea Tolea(1,2), Bogdan Grecu(1), Dragos Tataru(1), Bogdan Zaharia(1), Eduard Necula(1), Alexandru Tiganescu(1)
*
Affiliation:
1) National Institute for Earth Physics, Magurele, Romania
2) Faculty of Physics, University of Bucharest, Bucharest, Romania
E-mail
tolea.andreea@infp.ro
Keywords:
site characterization, Spatial Autocorrelation method (SPAC), microtremor array measurements (MAM), Multichannel Analysis of Surface Waves (MASW)
Abstract:
Geological and geotechnical surveys of a site provide all the necessary information about the quality and properties of the soil. Atom 3C are newly 3 channels wireless seismographs which can collect passive data from ambient seismic noise (ASN) for microtremor array measurements (MAM) and active data, using a sledgehammer as a seismic source for Multichannel Analysis of Surface Waves (MASW), two geophysical methods widely used for measuring shear-wave velocity distribution at depths of tens of meters. The MAM method is based on the analysis of ASN that originates from different sources including human activities, traffic, wind and ocean waves. The MAM method can be applied using different array geometries, such as linear array, circular arrays, triangle arrays. The choice of array geometry depends on the specific requirements of the study, such as the size and shape of the study area, the desired resolution, and the availability of equipment and personnel. The MASW, on the other hand, uses surface wave signals generated by a sledgehammer as a seismic source and several seismographs placed in a linear array. For the MAM technique, data processing can be performed using the Spatial Autocorrelation method (SPAC), whereas for the MASW technique, the recorded data is converted into frequency-wavenumber spectrum. MAM and MASW methods estimate the phase velocity of the ‘passive’ (ASN) or ‘active’ (generated by artificial sources) surface waves. The phase velocity is related to the subsurface shear-wave velocity (Vs) through a dispersion relation (dispersion curve). By inverting the dispersion curve, the Vs profile of the subsurface can be determined. The Vs30 parameter (average Vs to 30 m depth) is commonly used in seismic hazard assessments to account for the local site effects and has been incorporated in seismic design codes in many countries around the world. Finally, we exemplify the application of these methods on datasets obtained using different array geometries, including L-shape, triangle or linear arrays.
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