### Abstract

We investigate fault friction from dynamic modeling of fault slip prior to and following the M_{w} 6.0 earthquake which ruptured the Parkfield segment of the San Andreas Fault in 2004. The dynamic modeling assumes a purely rate-strengthening friction law, with a logarithmic dependency on sliding rate: μ=μ *+a-blnvv*. The initial state of stress is explicitly taken into account, and afterslip is triggered by the stress change induced by the earthquake source model given a priori. We consider different initial stress states and two coseismic models, and invert for the other model parameters using a nonlinear inversion scheme. The model parameters include the reference friction μ_{*}, the friction rate dependency characterized by the quantity a-b, assumed to be either uniform or depth dependent. The model parameters are determined from fitting the transient postseismic geodetic signal measured at continuous GPS stations. Our study provides a view of frictional properties at the kilometers scale over the 0-15 km depth illuminated by the coseismic stress change induced by the Parkfield earthquake. The reference friction is estimated to be between 0.1 and 0.5. With independent a priori constraints on the amplitude of differential stress, the range of possible values narrows down to 0.1-0.17. The friction rate coefficient a-b is estimated to be ∼ 10^{- 3} - 10^{- 2} with a hint that it increases upward from about 1-3 × 10^{-3} at 3-7 km depth to about 4-7 × 10^{-3} at 0-1 km depth. It is remarkable that our results are consistent with frictional properties measured on rock samples recovered from the fault zone thanks to the San Andreas Fault Observatory at Depth experiment.

Original language | English |
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Pages (from-to) | 3431-3447 |

Number of pages | 17 |

Journal | Journal of Geophysical Research: Solid Earth |

Volume | 118 |

Issue number | 7 |

DOIs | |

Publication status | Published - 1 Jul 2013 |

### Keywords

- afterslip
- fault friction
- Parkfield
- rate-strengthening

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## Cite this

*Journal of Geophysical Research: Solid Earth*,

*118*(7), 3431-3447. https://doi.org/10.1002/jgrb.50231