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

Abstract

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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