Speaker: Jens-Erik Lund Snee
U.S. Geological Survey
Stress Mapping and Induced Seismicity
Jens-Erik Lund Snee is a Mendenhall Research Fellow at the U.S. Geological Survey. Dr. Lund Snee is a geologist and geophysicist who studies tectonics and geomechanics, with focus on induced seismicity and tectonic history. He received his Ph.D. in Geophysics from Stanford University, where he developed a next-generation map of the state of stress in North America, with applications to induced seismicity, continental dynamics, and oil, gas, and geothermal development. Dr. Lund Snee also 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 U.S. He was 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.
Understanding the state of stress is important for managing induced seismicity because it enables identification of the faults most likely to fail seismically due to changes in pore pressure. In this talk, I will 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 the first quantitative map of the style of faulting (relative stress magnitudes) for the continent, focusing on areas where induced seismicity has recently occurred. In central and northern Oklahoma and southern Kansas, SHmax is consistently oriented ~ENE–WSW, with minor variability. In this area, the faulting regime becomes less compressive northward, from strike-slip faulting in central Oklahoma to dominantly normal faulting with some strike-slip faulting in southern Kansas. In contrast, marked rotations of SHmax are apparent to the west in the Rocky Mountain region, where normal and/or strike-slip faulting are active. Moving south from Oklahoma into northeast Texas, SHmax rotates markedly to be ~NE–SW throughout much of the Fort Worth Basin (FWB). Over this same area, the faulting regime becomes less compressive, with normal/strike-slip faulting in the northern FWB and normal faulting in the southern FWB. Along the Eagle Ford trend to the south, normal to normal/strike-slip faulting is active and SHmax is broadly parallel to the Gulf Coast. To the northwest, in the Midland Basin and Central Basin Platform (subdomains of the Permian Basin in west Texas and southeast New Mexico), SHmax is consistently ~E–W, and normal/strike-slip faulting predominates. However, immediately to the west in the Delaware Basin, normal faulting is dominant and SHmax rotates ~150° clockwise from north to south. Focal mechanisms from recent felt earthquakes suspected to have been triggered by industrial activities in several parts of Texas and throughout the central USA, including the March 2020 M5.0 Mentone, Texas, earthquake that occurred in the central Delaware Basin, show that the causative faults were usually well aligned with the stress field. Consequently, only small increases in pore pressure (typically <2 MPa at hypocentral depths and possibly much less in some cases) appear to have been necessary to trigger most of these events.
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