[ghsc-seminars] GHSC Seminar TOMORROW—Jens-Erik Lund Snee, USGS, Tuesday, March 8th, 2022, 10–11am MST

Mon Mar 7 21:29:04 UTC 2022

Next-generation crustal stress maps: Utility for understanding active tectonics and seismic hazards

Speaker: Jens-Erik Lund Snee
                Mendenhall Research Fellow
                USGS
Location: online/virtual
Date/Time: TOMORROW, Tuesday, March 8th, 2022, 10–11am MST

Abstract: Understanding the crustal stress field is important for anticipating the hazards of both natural and induced earthquakes because it enables identification of the faults most likely to fail seismically. In this talk, I present a next-generation stress map of North America that includes hundreds of new orientations of the maximum horizontal principal stress (SHmax) as well as a new, quantitative map of the style of faulting (relative stress magnitudes). In eastern North America, SHmax is broadly NE–SW, and reverse and/or strike-slip faulting are active. Moving westward into the midcontinent, the style of faulting becomes less compressive and SHmax gradually rotates clockwise westward, with SHmax oriented ENE–WSW and dominantly strike-slip faulting active in most of Oklahoma. The western U.S. is dominantly extensional, with normal and/or strike-slip faulting active in most areas. In that part of the continent, we observe major (up to 90°) rotations of SHmax, principally near the margins of extensional provinces. Focal mechanisms from recent felt earthquakes suspected to have been triggered by industrial activities in several parts of the central USA, including parts of Texas and Oklahoma, show that the causative faults are often well aligned with the stress field. Consequently, only small increases in pore pressure (typically <2 MPa at hypocentral depths) were apparently necessary to trigger most of these events. Using the new datasets, I present several implications for geodynamics and understanding seismic hazards, including how constraints on relative stress magnitudes can be used to estimate bounds on absolute principal stress magnitudes. Profound differences between the observed stress and strain rate fields in much of eastern North America illustrate the much lower stress perturbations and shorter time scales associated with postglacial rebound (<2 MPa at 10 km depth near Hudson Bay over ca. 10 kyr) compared with the stresses already stored in the crust (>300 MPa in the same area) due to tectonic activity. Finally, I discuss work that is currently underway to determine ways that stress information might be used to improve probabilistic seismic hazard analysis (PSHA).

[cid:cf00d566-4dd3-42f5-85d2-dd5b2d9156c7]

Bio: Jens-Erik Lund Snee is a Mendenhall Research Fellow in the Geosciences and Environmental Change Science Center in Lakewood. Dr. Lund Snee is a geologist and geophysicist who studies tectonics and geomechanics at a range of scales. His postdoctoral research focuses primarily on the tectonic history and active tectonics of the western USA as part of the Geologic Framework of the Intermountain West project. He received his Ph.D. in Geophysics from Stanford University, where he developed a new-generation map of the state of tectonic stress in North America, with applications to induced seismicity, continental dynamics, and oil, gas, and geothermal energy development. Dr. Lund Snee received his M.S. in Geological & Environmental Sciences from Stanford, where he studied the tectonic and paleogeographic history of the Great Basin in the western USA. He was previously awarded a Fulbright Fellowship to study the Alpine Fault plate boundary system in New Zealand, and his experience includes work for Statoil (now Equinor) as a hydrocarbon exploration geologist in the deepwater Gulf of Mexico, and for the U.S. Forest Service.

GHSC Seminar Committee: Oliver Boyd <olboyd at usgs.gov>, Josh Rigler <erigler at usgs.gov>, Francis Rengers <frengers at usgs.gov>

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