State of stress in intraplate areas of the conterminous USA: Induced seismicity and new tectonic questions

Jens‐Erik Lund Snee

Stanford University

Date & Time
Building 3, Rambo Auditorium

Over the past five years, the Stanford Stress and Geomechanics Group has compiled about 500 new orientations of the maximum horizontal stress (SHmax) throughout the central and eastern USA. The data continue to reveal remarkable coherence over large parts of the region and at various depths in the brittle crust. In addition, we have advanced mapping of the stress field by also interpolating relative magnitudes of the principal stresses. Reverse faulting is active across the northeastern USA and southeastern Canada, but the faulting regime becomes less compressive westward and southward, with reverse/strike-slip faulting in parts of Appalachia and the Southeast, and dominantly strike-slip faulting in much of the Midwest and South, and westward into Oklahoma. The faulting regime is more extensional further west, with normal and normal/strike-slip faulting in the Great Plains and parts of the Rocky Mountains.

Consistent with previous stress maps of this region, there are broad regions of consistent SHmax orientation. For example, SHmax is ENE–WSW to NE–SW across most of the Eastern seaboard, Midwest, and Southeast. However, the greatly improved data now available indicate several areas displaying unusually abrupt changes in stress orientation. Southward from central Oklahoma (where SHmax is approximately E–W and there is a strike-slip stress state), SHmax rotates counter-clockwise southward to become nearly NNE–SSW in the Fort Worth Basin of northeast Texas. Southwest of there, SHmax rotates clockwise, becoming E–W in the Midland Basin and Central Basin Platform in the Permian Basin of west Texas. In the Delaware Basin of the western Permian Basin, there is a marked 150° clockwise rotation from north to south. In northwest Montana and the Williston Basin of North Dakota, SHmax is NE–SW, but it rotates clockwise southward to E–W in parts of western South Dakota, eastern Colorado, and western and central Oklahoma. Further west, SHmax is approximately N–S along the Rio Grande Rift of central Colorado to northeast Mexico. West of the Rio Grande Rift, on the Colorado Plateau and Rocky Mountains, SHmax regains an E–W component, but it gradually rotates northward to be NW–SE in northwest Colorado and western Wyoming.

The coherent stress variations that we document are essential for identifying faults likely to slip in earthquakes and for planning horizontal well paths. Our SHmax measurements, which were made using traditional wellbore and seismic methods, provide a “ground truth” that can be used to validate novel techniques recently proposed to measure or model the stress field.

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