Uncertainty Estimation on Active Surface-Waves Based Tests

Abstract

Geophysical methods based on surface waves have become very popular in recent decades due to their versatility and reduced cost of execution compared to other invasive techniques. Due to space constraints in urban environments, measurements with linear arrays using active and passive techniques are usually combined to reach the exploration depth required by seismic site classification regulations. Although several good practice guidelines have been developed for performing this type of geophysical explorations, one of the remaining major challenges is to relate the results of these explorations to uncertainty metrics. In the case of active tests, there are effects associated with the filtering method used to eliminate the near and far-field effects, as well as other difficulties related to higher Rayleigh-modes or heterogeneities of the site. In this paper, we study the effect of body waves unavoidably induced in active tests on the proper determination of the dispersion curve of a site. For this purpose, active tests are carried out using triaxial geophones to extract from the records the motion effectively corresponding to Rayleigh waves by means of the Normalized Inner Product (NIP) technique. The results show that the effects of body waves are negligible for frequencies above about 8 Hz, but below this value, in the transition zone with ESPAC passive tests, the differences can be more significant. These results are used to introduce uncertainty indicators in this type of explorations

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