Mapping soft soils in the Segura river valley (SE Spain): A case study of microtremors as an exploration tool

This study analyzes the spatial distribution of soft soils in a valley with a significant amount of recently accumulated (Late Pleistocene-Holocene) sediments, but where the available geotechnical information on the subsurface is inadequate to study the entire valley. To analyze this distribution, we have used a new geophysical prospecting technique, which consists of estimating the thickness of soft soils based on their resonance frequency. This frequency has been determined from the H/V ratios of microtremors measured at 180 sites in the valley. The results indicate the generalized presence of soft soils along almost the entire valley, with thicknesses of up to 67 m. Based on the interpolation of the results, we have drawn up a map showing the spatial distribution and thickness of the soft soils in the valley. This map is of great interest both for future plans regarding the use of the soil in the region as well as for seismic zoning and soil-response studies.