State of stress in areas of induced seismicity across North America

Abstract:

Understanding the state of stress enables identification of the faults most likely to fail seismically due to changes in pore pressure associated with industrial activities. As part of a new-generation stress map of North America, we show the maximum horizontal stress (S_Hmax) orientation and relative principal stress magnitudes (style of faulting) in the areas where induced seismicity has occurred in recent years. In central and northern Oklahoma and southern Kansas, the orientation of S_Hmax is consistently ~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. However, moving south to northeast Texas, S_Hmax 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 S_Hmax 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), S_Hmax is consistently ~E–W, and normal/strike-slip faulting predominates. However, immediately to the west in the Delaware Basin, normal faulting is dominant and S_Hmax rotates ~150° clockwise from north to south. Focal mechanisms from recent seismicity in this area, including the M5.0 Mentone earthquake, reflect the marked rotation of S_Hmax, indicating that seismicity is occurring on faults that are well oriented to the regional stress field. For most induced events in the central USA, the faults are well aligned to the mapped stress field and 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 slip.