SCEC Award Number 12148 View PDF
Proposal Category Collaborative Proposal (Integration and Theory)
Proposal Title How much stress is accumulating on the creeping section of the San Andreas Fault?
Investigator(s)
Name Organization
Kaj M. Johnson Indiana University Paul Segall Stanford University
Other Participants Andrew Bradley, postdoc, Stanford
Andreas Mavrommatis, grad student, Stanford
Jeremy Mauer, grad student, Indiana
SCEC Priorities 1b, 2d, 4e SCEC Groups SDOT, Geodesy, Geology
Report Due Date 03/15/2013 Date Report Submitted N/A
Project Abstract
 The creeping section of the San Andreas fault (CSAF) in central California is a proposed barrier to propagation of large earthquakes. Yet, recent studies show that that the creeping section is not entirely uncoupled but is accumulating slip deficit at a rate equivalent to a Mw=7.2-7.4 earthquake every 150 years. A critical piece to understanding earthquake potential on the CSAF is determining whether slip deficit is occurring with stress accumulation on stick-slip regions or without stress accumulation on stable-sliding regions shadowed by surrounding locked areas. We use a physical model to estimate the spatial distribution of locked, stress-accumulating areas of the fault constrained by surface creep rate measurements and GPS-derived velocities. We find that the area of the fault accumulating stress, if ruptured every 150 years, would release slip equivalent to at most a Mw = 6.75 earthquake, significantly less than the Mw=7.2-7.4 150-year-equivalent total slip deficit rate.
Intellectual Merit This work quantifies the degree of coupling on the creeping section of the San Andreas fault and shows that there likely is stress accumulating on the fault that would presumably be building up for future earthquakes. However, we show that only a relatively small area of the fault is likely locked and therefore only moderate-sized earthquakes would be expected to nucleate within the creeping zone. The work has implications for future UCERF activities.
Broader Impacts The funding for this work helped support a graduate student, Jeremy Maurer.
Exemplary Figure Figure 2. Model geoemtry and estimates of locking and interseismic creep rates. Blue lines show model faults (block boundaries). (a-c) Color indicates the probability that a patch is locked for three different inversions (N is number of locked patches in constrained inversions). (d-f) Distribution of interseismic creep rate for three inversions. Mean of MCMC distributions. Numbers indicate long-term right-lateral fault slip rate in mm/yr (positive is right lateral).
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