3D insight into fault geometries, deformation, and fluid-migration within the Hosgri Fault Zone offshore central California: Results from high-resolution 3D seismic data

Abstract:

High-resolution 3D seismic P-Cable data and advanced seismic attribute analyses were used to detect and interpret complex strike-slip fault geometries, deformation patterns, and fluid-pathways across a portion of the Hosgri Fault Zone (HFZ) offshore central California. Combination of the fault attribute results with structural analysis provides 3D insight into the geometry and internal structure of restraining and releasing bends, step-over zones, fault convergence zones, and apparent paired fault bends. The 3D seismic volume covers a 13.7 km² region along the HFZ offshore of Point Sal and was collected in 2012 as part of the PG&E Central California Seismic Imaging Project (PG&E, 2014). Application of the fault attribute workflow isolated and delineated fault strands within the 3D volume. These results revealed that the northern and southern edges of the survey region are characterized by single fault strands that exhibit an approximate 6° change in strike across the 3D volume. Between these single faults strands is a complex network of fault splays, bends, stepovers, and convergence zones. Structural analysis reveals that the southern portion of the HFZ in the region is characterized by transtensional deformation, whereas transpressional-related folding dominates the central and northern portions of the HFZ.  In the central region, convergence of the Lions Head Fault from the southeast results in an apparent impinging block, leading to development of a “paired fault bend” to the west. Combination of the fault and “chimney” attribute results indicates a strong connection between faults and fluid-migration pathways. Fluid-pathways are concentrated along discrete faults in the transtensional zones, but appear to be more broadly distributed amongst fault bounded anticlines and structurally controlled traps in the transpressional zones.