High-resolution, Two-Dimensional Geophysical Investigation of several small faults at the northern end of the Hat Creek graben, Shasta, Californi

Abstract:

Several faults were identified as Quaternary in age near the Pit River at the northern end of the Hat Creek graben based on their geomorphic expression. Preliminary paleoseismic trenching confirmed that Fault 3432 had displacements in the late Quaternary indicating that it is with long recurrence, but the style of faulting and its role within the greater geologic context remains unresolved. Detailed site-specific geophysical investigations were performed in order to help characterize the Fault 3432 and plan future paleoseismic investigations. Seven two-dimensional seismic reflection lines were acquired using a distributed networked recording configuration. Standard seismic reflection processing and surface wave processing using IMASW were performed to resolve shallow stratigraphy within Camp Shasta Basin and Burney Mountain Hillside Basin locations. Using this data combined with geomorphology facilitated our mapping and interpretation of fault zone architecture within the study area. In both Camp Shasta and Burney Mountain locations, seismic reflection data helped locate discrete fault strands extending near surface. In addition, our interpretation of seismic profiles show that near-vertical steep faults merge at depth indicating negative flower structure. This fault structure suggests that the dominant style of faulting in the study area is strike slip with a normal component.