Probabilistic inversion of towed TEM data to map hazardous quick clays

A towed transient electromagnetic (tTEM) data set collected in a quick clay site in Sweden was used to test applicability of a new probabilistic inversion methodology. Areas containing quick clay are prone to landslides and there are recent occurrences of such events. The area is well-studied by other geophysical techniques and geotechnical data from various investigations are available. The methodology efficiently handles localized 1D inverse problems by sampling from the posterior probability distribution of model parameters and likelihood information from measurements. It uses an extended rejection sampler and creates a lookup table with given prior realizations while it carries out forward responses. This many advantages including efficient incorporation of prior geological information, comprehensive uncertainty quantification, hypothesis testing between competing models, efficient reuse of lookup tables across the study area, and output that includes both resistivity models and probability distributions of quick clay presence. Application of the new technique to the collected tTEM data has provided new insight regarding the identification of areas with higher probability of presence of quick/leached clay where these types of clays were identified by geotechnical borehole and laboratory observations. The method is for 1D inversion and can be extended for 2D/3D which is more computational demanding.