Geological Controls on natural hazards in Ixhuatlan de Madero, Veracruz, Mexico

The Ixhuatlan de Madero area is located (in the geology of Mexico) between the Gulf of Mexico and the micro-continent Oaxaquia. The regional stratigraphy comprises the Paleocene Chicontepec Formation (chiefly sandstones and shales), overlying the Cretaceous Mendez and Tamaulipas formations, respectively composed of shales and limestones. Analysis of the structural data collected in the field indicates five stages of deformation. The first stage is characterized by upright folds plunging to the NE and SW. The second stage corresponds to the Laramide orogeny (i.e. ~ 40 Ma) and involves NE-vergent folds. The folding produced south-westwards shallow-dipping layers (i.e. less than 30°) and overturning of the first stage folds to the NE. The third stage is marked by reverse faults compatible with NE-SW compression as observed in the village of Cantollano. In contrast, NW-SE normal faults observed to the NW of Ixhuatlan reveal a fourth stage characterised by an extensional regime. The fifth stage involves NW-SE and NE-SW fractures present mainly west of Ixhuatlan de Madero. The latter fractures represent pronounced weakness zones within the rock mass and are further opened by plant roots and excavated by the tropical rains of the region. The control local disintegration of the rock and lead eventually to landslides. The landslides promote mass transport towards the NE and SW dominantly and, furthermore, the building of houses and human infrastructures amplify them.