Tilts, strains, and groundwater levels near an earth fissure in the Mimbres Basin, New mexico

Vertical deflection profiles derived from microradian-sensitivity tiltmeter data collected over a one year period suggest that an earth fissure in the subsiding Mimbres basin is located near the infllection point of an evolving surficial fold of infinitesimal amplitude. Water levels beneath the study site also fell steadily during the period of observation. Observed perpendicular tilts and the location of the fissure at an inflection point rather than along an anticlinal crest are consistent with a mode II fracture (shearing mode crack or fault) rather than a mode I fracture (opening mode crack or joint). Tilting parallel to the fissure further suggests a component of mode II (Tearing-mode crack) displacement during the study period. On the basis of the occurrence of right steps in the trace of fissure, we speculate that our data may reflect contraction across one of the steps as a consequence of left-lateral slip along the fissure. -from Authors