Strain Accommodation Within Emerging Shear Zones: Insights From the Centennial Shear Zone, Montana and Idaho

SSHAC Level 1 Probabilistic Seismic Hazard Analysis for the Idaho National Laboratory

“…This result is similar to the of N78±4°W for the direction of strike-slip derived from the geodetic principal horizontal strain rate (Payne et al, 2013). Parker and Sears (2016) also concluded that the strain was distributed across high-angle strike-slip faults (mean strike of 200±20.0° and dip of N78°W) in a primary deformation zone consistent with the zone proposed by Payne et al (2013). They further suggest that a localized simple shear stress field (σ 1 horizontal) is superimposed over the regional extensional stress field in the CSZ.…”

“…As an example, Bruhn et al (1992) interpreted that NE-striking cross faults associated with an asymmetrical NE-trending graben in the footwall of the Lemhi fault provides a means to accommodate differential motion between the southern end of the Lemhi fault and ESRP over the last 4 m.y. Another example is offered by Parker and Sears (2016) who found a distributed strain across high angle conjugate strike-slip faults in an 800-m thick quartzite comglomerate of Neogene age within the CSZ.…”

“…The recent work of Parker and Sears (2016) measured and evaluated sedimentary structures and pressure-solution pit dimensions in cobbles of a 365,000 yr old, 800-m thick quartzite comglomerate within the CSZ. From their data, they estimated a maximum horizontal principal stress orientation for σ 1 as 255.8±22.0° (or 75.8±22.0°).…”

“…Within the CSZ, strikes, dips, and dip directions of NE-trending normal faults from field measurements (Zentner, 1989;Janecke, 1992;Rodgers et al, 2002) and fault plane solutions (Stickney, 1997; were used to assess the distributions of these parameters listed in Table 8-3 for the SSC model. For the ATR, the strike orientations were revised to include the results of Parker and Sears (2016) who found the strikes of strikeslip faults and related fractures to be 200±20.0°.…”