Seismic cycle and rheological effects on estimation of present-day slip rates for the Agua Blanca and San Miguel-Vallecitos faults, northern Baja California, Mexico

Timothy Dixon, Julien Decaix, Fred Farina, Kevin Furlong, Rocco Malservisi, Richard Bennett, Francisco Suarez-Vidal, John Fletcher, Jeff Lee

Research output: Contribution to journalArticle

33 Scopus citations


Geodesy can be used to infer long-term fault slip rates, assuming a model for crust and upper mantle rheology. We examine the sensitivity of fault slip rate estimates to assumed rheology for the Agua Blanca and San Miguel-Vallecitos faults in northern Baja California, Mexico, part of the Pacific-North America plate boundary zone. The Agua Blanca fault is seismically quiet, but offset alluvial fans indicate young activity. Current seismicity is confined to the nearby San Miguel-Vallecitos fault, a small offset fault better aligned with plate motion. GPS measurements between 1993 and 1998 suggest that both faults are active, with a combined slip rate of 4-8 mm yr-1 regardless of rheological model. However, slip rate estimates for the individual faults are sensitive to assumed rheology. Elastic half-space models yield 2-3 mm yr-1 for the Agua Blanca fault, and somewhat faster rates for the San Miguel-Vallecitos fault, 2-4 mm yr-1, with uncertainties of about 1 mm yr-1. Models incorporating viscoelastic rheology and seismic cycle effects suggest a faster slip rate for the Agua Blanca fault, 6 ± 1 mm yr-1, and a slower rate for the San Miguel-Vallecitos fault, 1 ± 1 mm yr-1, in better agreement with geological data, but these rates are sensitive to assumed rheology. Numerical simulations with a finite element model suggest that for similar rheological and friction conditions, slip on the San Miguel-Vallecitos fault should be favored due to better alignment with plate motion. Long-term faulting processes in the larger offset Agua Blanca fault may have lowered slip resistance, allowing accommodation of motion despite misalignment with plate motion.

Original languageEnglish (US)
Pages (from-to)ETG 5-1 - 5-23
JournalJournal of Geophysical Research: Solid Earth
Issue number10
StatePublished - Oct 10 2002
Externally publishedYes



  • Fault slip rates and the seismic cycle
  • Northern Baja California

ASJC Scopus subject areas

  • Geophysics
  • Geochemistry and Petrology
  • Earth and Planetary Sciences (miscellaneous)
  • Space and Planetary Science

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