The relationship betweenin situ strain relaxation and outcrop fractures in the Potsdam Sandstone,Alexandria Bay,New York

Summary In situ strain was measured by overcoring foil-resistance strain gauge rosettes bonded to five outcrops of Potsdam Sandstone near Alexandria Bay, New York. Strain relaxation magnitude and orientation correlated with the area of the intact outcrop outlined by intersecting vertical fractures. The maximum expansion occurred at the outcrop with the largest area between intersecting fractures. Outcrops with more than one set of longer, open fractures or more complicated fracture patterns have lower recoverable strains. Strain relaxation was lowest next to a postglacial pop-up. The orientation of the pop-up indicated relief of an ENE directed compression, the direction also observed as the maximum expansion at the outcrop yielding the largest strain relaxation.Lamont-Doherty Geological Observatory Contribution No. 2456.