Geophysical characterization of soil deformation associated with earth fissures near san marcial and deming New Mexico

Seismic reflection profiles across two earth fissures show that surficial strata are draped over a buried normal fault scarp beneath one fissure and over a buried channel deposit beneath the other. P-wave velocity contour plots also show anomalies near both fissures. Gravity profiles suggest the presence of buried structures, but provide comparatively little information about the geologic setting of the fissures. Mechanical analysis of a compressible elastic soil layer draped over steps shows that the most tensile stresses will develop along the upper free surface if the steps are wide and along the base of the layer if the steps are narrow. We conclude that geometric details of buried irregularities control whether a fissure propagates upward from depth or downward from the ground surface. Moreover, details of stress trajectory fields can control the position of a fissure at the earth's surface relative to bedrock irregularities at depth.