Influences of variations in the sledgehammer trajectory and collinearity of the geophone array in an MASW survey on the shear-wave velocity profile

Abstract

Abstract In professional activities aimed at seismic site classification, geophysical methods based on measurements of surface waves are often used to measure the shear-wave velocity (Vs), with the MASW survey being one of the most common techniques employed for this purpose. An MASW survey is characterized by an in-field configuration that requires a relatively simple setup; however, several uncertainties that arise are related to the survey execution process. Thus, surface irregularities and/or obstacles on the ground surface in conjunction with possible human-related errors can result in alterations to the MASW survey execution. Therefore, it is necessary to possess a clear understanding of the variables that can potentially produce alterations in Vs profiles. The purpose of this study was to evaluate, based on a field measurement campaign, the effect of the repeatability of the sledgehammer trajectory prior to striking the plate and the effects of variations in the collinearity of the geophone arrays on the Vs profile in consideration of various forced alterations commonly encountered in practice. The repeatability of the active source trajectory plays a significant role in the quality and reliability of Vs measurements. Likewise, altering the collinearity of the geophone array leads to reductions in the amplitude at low frequencies, thereby hindering the interpretation of the test. The recorded effects become more relevant depending on the local conditions and whether the surveyed terrain exhibits possible heterogeneity.

Keywords

• Measurement uncertainties
• Alterations of geophone array
• Multichannel analysis of surface waves MASW
• Geophysical site investigation
• Shear wave velocity