Refining the Spatial and Temporal Signatures of Creep and Co-Seismic Slip Along the Southern San Andreas Fault Using Very High Resolution SfM Imagery, Coachella Valley, California

Chelsea M. Blanton, Thomas K. Rockwell, & Allen M. Gontz

In Preparation May 15, 2019, SCEC Contribution #9088

Structure from Motion (SfM) Photogrammetry, based on unmanned aerial vehicle (UAV) flights, was implemented along the southern San Andreas fault (sSAF) to acquire a dense, high-resolution topographic dataset from which to interpret fault-related offsets of small geomorphic features and to develop a model of late Holocene slip-per-event. This study better constrains slip estimates from recent earthquakes along the sSAF and combines new slip data with ages of past earthquakes from paleoseismic studies. We evaluate slip per event for paleoearthquakes which ruptured this segment of the sSAF and investigate the relationship between co-seismic slip events and creep or afterslip and triggered slip. Statistical analysis of our offsets suggests five (5) large, surface rupturing events with average displacements of 2.6 – 3.1 m per event according to our preferred model. Gaussian distribution analysis reveals small-scale offset clusters that we attribute to climate-modulated channel incision across the fault and subsequent creep. We hypothesize that large precipitation events could have incised new rills and channels across the fault, generating small offsets as the fault crept. These offset clusters support a creep rate of ~3 mm/yr in the northern Mecca Hills and Box Canyon averaged over the past ~160 years.

Key Words
Paleoseismology, Tectonic Geomorphology, Low-altitude photogrammetry, El Niño

Citation
Blanton, C. M., Rockwell, T. K., & Gontz, A. M. (2019). Refining the Spatial and Temporal Signatures of Creep and Co-Seismic Slip Along the Southern San Andreas Fault Using Very High Resolution SfM Imagery, Coachella Valley, California. Geomorphology, (in preparation). https://www.journals.elsevier.com/geomorphology