MASW Seismic Method in Brebu Landslide Area, Romania

World Multidisciplinary Earth Sciences Symposium 2017

Mihai, Marinescu^1 ; Paul, Cristea^2 ; Cristian, Marunteanu^1 ; Matei, Mezincescu^1

University of Bucharest, 36-46, M. Kogalniceanu Blvd, Romania^1

Geological Institute of Romania, 1 Caransebes St., Bucharest, Romania^2

关键词: Dynamic elastic property;    Geotechnical information;    Longitudinal elastic modulus;    Longitudinal wave velocity;    Multi-channel analysis of surface waves;    Parameter evolution;    Resonance frequencies;    Seismic data processing;   

Others  :  https://iopscience.iop.org/article/10.1088/1755-1315/95/3/032035/pdf
DOI  :  10.1088/1755-1315/95/3/032035

来源: IOP

【 摘 要 】

This paper is focused on assessing the possibility of enhancing the geotechnical information in perimeters with landslides, especially through applications of the Multichannel Analysis of Surface Waves (MASW) method. The technology enables the determination of the phase velocities of Rayleigh waves and, recursively, the evaluation of shear wave velocities (Vs) related to depth. Finally, using longitudinal wave velocities (Vp), derived from the seismic refraction measurements, in situ dynamic elastic properties in a shallow section can be obtained. The investigation was carried out in the Brebu landslide (3-5 m depth of bedrock), located on the southern flank of the Slanic Syncline (110 km North of Bucharest) and included a drilling program and geotechnical laboratory observations. The seismic refraction records (seismic sources placed at the centre, ends and outside of the geophone spread) have been undertaken on two lines, 23 m and 46 m long respectively) approximately perpendicular to the downslope direction of the landslide and on different local morpho-structures. A Geode Geometrics seismograph was set for 1 ms sampling rate and pulse summations in real-time for five blows. Twenty-four vertical Geometrics SpaceTech geophones (14 Hz resonance frequency) were disposed at 1 m spacing. The seismic source was represented by the impact of an 8kg weight sledge hammer on a metal plate. Regarding seismic data processing, the distinctive feature is related to performing more detailed analyses of MASW records. The proposed procedure consists of the spread split in groups with fewer receivers and several interval-geophones superposed. 2D Fourier analysis, f-k (frequency-wave number) spectrum, for each of these groups assures the information continuity and, all the more, accuracy to pick out the amplitude maximums of the f-k spectra. Finally, combining both values VS(calculated from 2D spectral analyses of Rayleigh waves) and VP(obtained from seismic refraction records) plots of mean geodynamic parameter evolution related to depth were constructed. Parameter value differentiations referring to slope stability are revealed. Lowest values of VS and both shear and longitudinal elastic moduli are defined for the area with landslide rockmass, in opposition with stable land for which the biggest values for same parameters are revealed. Intermediate values are signalized above the main plane of sliding, zone classified unstable.