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 H Dixon, J. Decaix, F. Farina, K. Furlong, Rocco Malservisi

Research output: Contribution to journalArticlepeer-review

Abstract

<p> Geodesy can be used to infer long&hyphen;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&hyphen;Vallecitos faults in northern Baja California, Mexico, part of the Pacific&ndash;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&hyphen;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&ndash;8 mm yr&minus;1 regardless of rheological model. However, slip rate estimates for the individual faults are sensitive to assumed rheology. Elastic half&hyphen;space models yield 2&ndash;3 mm yr&minus;1 for the Agua Blanca fault, and somewhat faster rates for the San Miguel&hyphen;Vallecitos fault, 2&ndash;4 mm yr&minus;1, with uncertainties of about 1 mm yr&minus;1. Models incorporating viscoelastic rheology and seismic cycle effects suggest a faster slip rate for the Agua Blanca fault, 6 &plusmn; 1 mm yr&minus;1, and a slower rate for the San Miguel&hyphen;Vallecitos fault, 1 &plusmn; 1 mm yr&minus;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&hyphen;Vallecitos fault should be favored due to better alignment with plate motion. Long&hyphen;term faulting processes in the larger offset Agua Blanca fault may have lowered slip resistance, allowing accommodation of motion despite misalignment with plate motion.</p>
Original languageAmerican English
JournalJournal of Geophysical Research: Solid Earth
Volume107
DOIs
StatePublished - Oct 1 2002
Externally publishedYes

Keywords

  • fault slip rates and the seismic cycle
  • northern Baja California

Disciplines

  • Earth Sciences

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