... More than 3.000 m of high resolution MASW surveys & more than 265 ReMi Soundings carried out and processed for engineering projects and geotechnical studies in South America between 2006 and 2016 ...
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MASW (Multichannel Analysis of Surface Waves)
The multichannel analysis of surface waves method (MASW) is a nondestructive seismic method to investigate shallow subsoil conditions as well as to evaluate linear elastic modulus of ground and subsoil materials. It analyzes dispersion properties of certain types of seismic surface waves (fundamental-mode of Rayleigh waves) propagating horizontally along the surface of measurement directly from impact point to receivers. It gives this shear-wave velocity (Vs) (or stiffness) information in either 1-D (depth) or 2-D (depth and surface location) format in a cost-effective and time-efficient manner. The main advantage with the MASW method is to take a full account of the complicated nature of seismic waves that always contain harmful noise waves such as higher modes of surface waves, body waves, scattered waves, traffic waves, etc. These noise waves may result in a significant portion of the recorded data being dubious if not properly accounted for. The fundamental framework of the MASW method is based on the multichannel recording and analysis approach long used in seismic exploration surveys. These techniques can discriminate useful signal against all other types of noise by utilizing pattern-recognition techniques.
Refraction Microtremor (ReMi) is a surface-wave seismic method for estimating in-situ Rayleigh-wave (shear-wave) velocities down to depths of 100 meters. Developed by Optim™ of Reno, Nevada, ReMi has a 5 to 15 percent accuracy, with the accuracy decreasing with depth. Rayleigh waves are surface shear-waves that are also known as “ground roll.” As the wave passes along the ground, each surface particle moves in a “retrograde elliptical” motion. This type of motion consists of a roughly circular path in a direction opposite the direction of propagation (see diagram). With depth, the ellipses become smaller and smaller, until there is no motion. Lower frequency waves produce elliptical particle motion deeper into the ground. Surface waves attenuate (decay) in amplitude more slowly than body waves, such as those recorded with seismic refraction, and therefore the ReMi technique can penetrate deeper into the subsurface for a given seismic array. Testing is performed at the surface using the same seismograph and vertical P-wave geophones as are used to acquire refraction data. ReMi data are recorded directly before or after the refraction data through the same geophone setup. The seismic source consists of ambient seismic noise, or microtremors, which are constantly generated by cultural and natural sources. In addition to the passive source noise, seismic noise can be induced by active sources. The data acquisition procedure consists of obtaining at least ten 30-second seismic noise records at a sample interval of 2 milliseconds. The result is a 1-D image of the subsurface shear-wave layering below the center of the geophone array.
Earthquake site response
IBC site classification based on 30m
average shear-wave velocity Site amplification maps
Mapping the subsurface and estimating the
strength of subsurface material
Coupled with P-wave information, one can derive Poisson’s ratio and other engineering parameters
Complementing seismic refraction analysis in areas characterized by near-surface velocity reversals
Maps low velocity zones that refraction cannot
Extends depth of investigation in some cases
Evaluating compaction quality
Advantages of Refraction Microtremor
ReMi compares well with previously used 1-D shear-wave measurement techniques
Determine subsurface properties
Derive parameters useful for geotechnical engineering
Determine properties of buried fill material
Perform site specific seismic characterization studies efficiently and economically