A REGIONAL KINEMATIC MODEL FOR HAT CREEK GRABEN, SHASTA COUNTY, CALIFORNIA; EVIDENCE FOR NORTHWARD PROPAGATION OF THE NORTHERN WALKER LANE

The northern Hat Creek graben provides a rare perspective on the behavior of closely-spaced faults and their relationship to complicated and evolving deformation in northeastern California. Analyzing 540 km² of 0.5-m-resolution LiDAR covering numerous late Pleistocene lava flows, we document two discreet styles of late Pleistocene to Holocene faulting in the region. Additionally, we recognize a temporal relationship between the associated kinematically distinct fault groups that has implications for the mid-to-late Pleistocene migration of Walker Lane dextral shear into the region.

We find that faults displacing the mid-to-late Pleistocene volcanic stratigraphy fall into two kinematic groups based on sense of slip, orientation, and location. Fault Group 1 encompasses an eastern set of faults that: (a) are oriented northwest-southeast and (b) display evidence of both normal dip slip and oblique dextral displacement as evidenced by en-échelon left stepping normal faults, right releasing bends/stepovers, and northwest-oriented mole tracks. Faults within this group are associated with the Hat Creek fault, the region’s predominant structure. Fault Group 2 encompass a western set of faults that: (a) are oriented primarily north to northeast and (b) display evidence of predominantly normal dip-slip and sinistral displacement evidenced by en-échelon right-stepping normal faults, localized pop ups along left (restraining) bends, and north-northeast oriented mole tracks. Based on orientations of macroscopic dextral and sinistral shear for Groups 1 and 2, respectively, the two groups do not comprise a conjugate fault set and are thus interpreted to be kinematically distinct.

Where Groups 1 and 2 intersect, Group 2 sinistral faults are either overtaken by or transition to Group 1 oblique dextral faults. This relationship suggests that, while both fault sets are active and have been since at least the mid Pleistocene, the NW-directed oblique dextral deformation associated with Group 1 now prevails and likely overprints earlier faulting associated with Group 2. We interpret this transition to predominantly northwest-oriented dextral shear as evidence of the relatively recent migration of Walker Lane deformation into the region from the southeast.