Revised (lower) slip rate for the Northern Death Valley Fault based on a new method for restoring alluvial fan cutoff lines

Karl J. Mueller, & Ragan Anthony

Published August 15, 2017, SCEC Contribution #7848, 2017 SCEC Annual Meeting Poster #222

Determining slip rates on active strike slip faults in Southern California at timescales of 103 – 105 years depends on recognition and measurement of offset landforms and deposits. While offset deposits can be directly age dated to determine slip rates, piercing points such as offset stream channels are often used to measure displacement. Direct age dating of offset stream channels is difficult and can lead to uncertainty in age associated with unknown rates of headward propagation of channel networks up abandoned fans. Recent studies in Death Valley rely on offset stream channels to estimate minimum slip rates on active strike slip faults. Yet the time lag between when stream channels begin to incise fan surfaces and when they have migrated far enough upslope to cross an active fault (i.e. and begin to record offset) is unknown. In addition, assumptions are often used when correlating offset channels in complex stream arrays that are offset by strike slip faults, creating additional uncertainty in slip rates determined at a particular site. We have developed a new method for restoring abandoned alluvial fan surfaces offset by strike slip faults that avoids uncertainty related to unconstrained correlation of offset stream channels. We develop a 3D model of the pre-faulted fan surface based on preserved parts of its upper surface at abandonment. We then project contours on the 3D model (at constant curvature) across a fault zone to define the two cutoff lines defined by the intersection of topographic contours on the fan surface on either side of the fault and a vertical plane coincident with the highest fault scarp at the site. This is similar to structural restorations of hangingwall and footwall cutoff lines of stratigraphic contacts offset by faults in the subsurface. Our preliminary study on the Northern Death Valley Fault Zone near Redwall Canyon suggests slip rates there are actually a small fraction (i.e. 1.1 versus 4.2 mm/yr) of what has been reported in previous work by Frankel et al., (2007) based on offset stream channels. These results are consistent with slip rates determined further south in Death Valley (i.e. ~ 1 to 2mm/yr), but remain at odds with a site further north with even higher slip rates of 6mm/yr (Frankel et al., 2011). We seek to further develop our new method by applying it to other active faults where alluvial deposits have been dated and by a more formal assessment of errors inherent in the technique.

Key Words
fault slip rates, Death Valley Fault zone, structural restoration of alluvial fans

Citation
Mueller, K. J., & Anthony, R. (2017, 08). Revised (lower) slip rate for the Northern Death Valley Fault based on a new method for restoring alluvial fan cutoff lines. Poster Presentation at 2017 SCEC Annual Meeting.

Related Projects & Working Groups
Stress and Deformation Over Time (SDOT)