Martin Hernandez-Marin

Correlation of near-surface stratigraphy and physical properties of clayey sediments from Chalco Basin, Mexico, using Ground Penetrating Radar

Detailed measurements of water content, liquid and plastic limits, electric conductivity, grain-size distribution, specific gravity, and compressibility were performed on the upper 7 m of the lacustrine sequence from the Chalco Basin, Valley of Mexico. Eight stratigraphic units consisting of alternating layers of clay, silt, sand, and gravel of volcanic origin are described for this sequence. The analysis of contrasts in the physical properties permitted to identify potential reflectors of radar waves: (i) change in the electrical conductivity at 0.4 m depth; (ii) increment in the clay and water content at 0.8 m depth; (iii) bimodal behavior of the water content at 1.3 m depth; (iv) increment in the sand content and decrease in water content at 2.6 m depth; and (v) the presence of a pyroclastic unit at 3.7 m depth. Radargrams with frequencies of 900 and 300 MHz were collected on a grid of profiles covering the study area. Correlation of radargrams with the reference section permitted the spatial interpolation of variations in the physical properties and the near-surface stratigraphy. Contrary to the expected in these clayey sediments, electric contrast enhanced by variations in water content and grain size permitted the recording of the near-surface sedimentary structures. Distinctive radar signatures were identified between reflectors. Furthermore, lateral discontinuities of the reflectors and their vertical displacements permitted the identification of deformational features within the sequence. D 2003 Elsevier B.V. All rights reserved.

Application of InSAR and Gravimetry for Land Subsidence Hazard Zoning in Aguascalientes, Mexico

In this work we present an application of InSAR and gravimetric surveys for risk management related to land subsidence and surface ground faulting generation. A subsidence velocity map derived from the 2007–2011 ALOS SAR imagery and a sediment thicknesses map obtained from the inversion of gravimetric data were integrated with a surface fault map to produce a subsidence hazard zoning in the city of Aguascalientes, Mexico. The resulting zoning is presented together with specific recommendations about geotechnical studies needed for further evaluation of surface faulting in these hazard zones. The derived zoning map consists in four zones including null hazard (stable terrain without subsidence), low hazard (areas prone to subsidence), medium hazard (zones with subsidence) and high hazard (zones with surface faulting). InSAR results displayed subsidence LOS velocities up to 10 cm/year and two subsidence areas unknown before this study. Gravimetric results revealed that the thicker sediment sequence is located toward north of Aguascalientes City reaching up to 600 m in thickness, which correspond to a high subsidence LOS velocity zone (up to 6 cm/year).