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Shallow Subsurface 3D Structural Imaging Near Diablo Canyon Power Plant, California, Using Active Seismic, Gravity, and Magnetic Data

New very-high-resolution shallow active-source 3D seismic reflection and 3D acoustic velocity (Vp tomography) data were acquired in 2012 for two study areas (Phase 1 and Phase 2) in the vicinity of Diablo Canyon Power Plant (DCPP). In 2011, 2D/3D reflection was acquired in the Irish Hills to image large scale structure.

23 Apr 2015
Jamey Turner, Janet Sowers, Josh Goodman, Lia Lajoie, Dan O’Connell, Stuart Nishenko


In 2012, very-hi-res data focused on imaging subsurface structure at and near
DCPP. The Phase 1 area was centered on DCPP and the ~1-km site radius to address NRC Reg. Guide 1.208 requirements. Reflection data were evaluated for down-dip geometries of known and inferred geologic structures, or identify previously unknown structures. Vp and S-wave 3D tomography volumes were used for reflection processing inputs and DCPP foundation velocity analyses. Miocene volcaniclastic Obispo Formation exposed in the Phase 1 area is intruded by a large volume of bedding-discordant diabase bodies with uniquely high Vp values (≥20,000 ft/sec). The 3D Vp model provides well-imaged 3D subsurface strain markers in Phase 1 area; no significant offset of Vp structure was observed. The Phase 2 study of the marine terrace southeast of DCPP evaluated possible splay faults that may hard-link the San Luis Bay fault system (e.g., Rattlesnake fault) and the offshore Shoreline fault zone. Marine terrace deposits 20 to 50 feet thick overlie a platform of subvertical Cretaceous Sandstone (Ks); top Ks was mapped by creating a depth-to-first-strong-reflector map. Three lineaments were identified across the platform, and no consistent bedrock step is seen across the previously mapped Rattlesnake fault. A previously mapped unnamed fault north of Phase 2 area coincident with a magnetic-anomaly lineament is observed in 2011 reflection data as a high-angle alignment of reflection terminations. We propose the name Irish Canyon fault for this structure, and hypothesize that it was an en echelon splay of the Tertiary San Miguelito-Shoreline fault system.


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