Preferential elongation directions are presented from 46 subvertical wells in northeastern Mexico from depth intervals ranging from 161 to 4,912 m. The measurements document a remarkably consistent west-east to northwest-southeast direction of the contemporary least horizontal stress in the upper crust of this intraplate region. In the regional neotectonic framework, the data suggest that Mexico north of the trans-Mexican volcanic belt is being stretched in west-east to northwest-southeast direction. The measurements from the area of the Laramide Chihuahua and Coahulia fold-thrust belts define the southern extend of the Basin and Range--Rio Grande rift stress province of the southwestern United States into northern Mexico.

The least horizontal in situ stress directions recorded in the Gulf Coastal Plain (Burgos and Tampico-Misantla Basins) are oblique to the continental margin of the Gulf of Mexico, but subparallel to the direction measured in the area of the Basin and Range--Rio Grande rift stress province. This suggests that the stress distribution in these basins is not mainly the result of gravitational loading as in the Gulf Coast stress province of the United States, but is controlled by the same lithospheric stress system that characterizes the Basin and Range-Rio Grande rift stress province. This is also supported by the north-south trending zone of Oligocence-Quarternary alkaline volcanism that crosses the Tampico-Misantla Basin. Furthermore, the data indicate that the active deformation of the Mexican Ridges fold belt, east of the study area in the Gulf of mexico cannot be caused by a compressional external tectonic load.

The direction of the least horizontal in situ stress measured in the area of the Laramide Sierra Madre Oriental fold-thrust belt in Hidalgo and San Luis Potosi States is consistent with that of the other zones. However, wellbore elongations were recorded less frequently and show a rather large circular variance, which suggests that the minimum and maximum horizontal far-field stresses are about equal in this area. ¿ American Geophysical Union 1987