SCEC Award Number 24164 View PDF
Proposal Category Individual Research Project (Single Investigator / Institution)
Proposal Title Frictional analysis of fault gouges in the northern transition region of the San Andreas fault creeping section
Investigator(s)
Name Organization
Heather Savage University of California, Santa Cruz
SCEC Milestones A1-3, A3-1, A3-6, B2-1, B2-2 SCEC Groups FARM, CEM, Seismology
Report Due Date 03/15/2025 Date Report Submitted 06/23/2025
Project Abstract
 The San Andreas fault is functionally divided by northern and southern locked zones and a creeping section in the middle. Previous work at the SAFOD borehole had concluded that fault creep in that area was due to the presence of weak clay minerals. In this work, we sampled the creeping section near San Juan Bautista, where the fault is creeping in a quartz gabbro lithology. We ran friction experiments on gouges from different fault strands – some of which are creeping and some are not. Our experiments found that there was no lithological or frictional difference between the strands, but that frictional healing was subdued in all experiments at low effective stress.
Intellectual Merit Through x-ray diffraction (XRD) and friction experiments over a range of stresses, we show that the gouges sampled at different fault strands within the San Andreas fault 1) Have the same lithology and 2) Have similar frictional steady-state value and healing rates. However, all of the samples show a strong dependence on effective normal stress, where friction and velocity dependence are both large at low stresses.
Broader Impacts This grant has supported UCSC grad student Julia Krogh. The impact of fault creep on the seismic potential of faults is a major unknown for determining a fault’s seismic hazard.
Project Participants Heather Savage (PI) and Julia Krogh (grad student) both at UCSC
Exemplary Figure none
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