A New Model for the Strike-Slip Response of Entrenched Drainages Derived From an Alluvial Terrace Sequence at the Littlerock Creek Along the Mojave Section of the San Andreas Fault
Description:
We explore how alluvial terraces form in the sheltered-corner (SC) of streams offset along strike slip faults as a function of the accumulation displacement (D) and of temporal variations of the stream erosive power (E). We combine new mapping and 10Be dating of the Littlerock Creek (LRC) terrace sequence at its intersection with the San Andreas Fault (SAF), and analysis of published flume experiments of strike-slip displaced streams. River incision at LRC is driven by rapid uplift and transpression. Elevyn terraces abandoned between 36 and 12ka are preserved in the SC on the downstream side of the SAF, only two of which are preserved on the upstream side. The fluvial architecture shows two sets of narrow terraces that measured parallel to fault strike are elevated along a similar gradient of ~6º. These sets are separated by two terraces that are 3-times wider with much lower along-strike gradient, and correlate temporally with the upstream terraces.
Applying our analysis of the flume experiments to the LRC record, we propose that the steeper terrace gradient provides a measure of the ratio of the uplift to strike-slip component, and was acquired during steady-state intervals with equilibrium between E and D. The intervening two-terraces interval is interpreted as a transient period, during which the geomorphic system evolved from lower E and higher deflection angle (the angle the stream intersects the fault) to higher E and lower deflection angle, leading to the abandonment of the upstream terraces. This sequence of events is supported by independent paleoclimate records of water discharge along the LRC. These results suggest that the stream response to D is governed by the following feedbacks: (1) E determines the extent of upstream-facing scarp erosion, which in turn (2) controls the deflection angle, and hence (3) the geometry of the SC. Quantitative analysis of the SC terrace stratigraphy along strike-slip displaced entrenched drainages might thus be used to derive cumulative displacements even in the absence of upstream piercing-points.
Session: From Earthquakes to Plate Boundaries: Insights Into Fault Behavior Spanning Seconds to Millennia [Poster]
Type: Poster
Date: 4/20/2023
Presentation Time: 08:00 AM (local time)
Presenting Author: Katherine Scharer
Student Presenter: No
Invited Presentation:
Authors
Adrien Moulin adrien.moulin@kaust.edu.sa King Abdullah University of Science and Technology |
Eric Cowgill escowgill@ucdavis.edu University of California, Davis |
Katherine Scharer Presenting Author Corresponding Author kscharer@usgs.gov U.S. Geological Survey |
Devin McPhillips dmcphillips@usgs.gov U.S. Geological Survey |
Arjun Heimsath aheimsat@asu.edu Arizona State University |
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A New Model for the Strike-Slip Response of Entrenched Drainages Derived From an Alluvial Terrace Sequence at the Littlerock Creek Along the Mojave Section of the San Andreas Fault
Category
From Earthquakes to Plate Boundaries: Insights Into Fault Behavior Spanning Seconds to Millennia