Both asymmetric and symmetric deformation models are able to fit the GPS observations in the azimuth N55. We confirm that the transverse compressive component of the deformation across the Hayward fault is negligible. The location of the strain measurable from the GPS observations in the SFBA and its related shear stress rate have a direct impact on the expected time-recurrence of large earthquake in the Bay Area (Thatcher, 1990). We argue that discriminating between the two models is necessary in order to better integrate the GPS observations into constraints on the seismic cycle deduced from the monitoring of the seismic events and long-term geological evidences.

Figure 2.41: Validation of the asymmetric hypothesis of motion across SAF and HAY faults. Both locking depths are equal to 10 km. We combine the velocity fields associated wth SAF and HAY. By varying the velocity along the Hayward (top) and San Andreas fault (bottom), keeping the other velocity fixed, we have determined the slip velocities of the HAY and SAF are respectively equal to 10 and 20 mm/yr. Some additional residuals are visible at the UCD1 site. This residual velocity could be explained by different sources such as the interseismic deformation related to Calaveras or Greenville faults.
\begin{figure}\epsfig{file=comparison_velo.hay.fixe.epsi, width=8cm}\epsfig{file=comparison_velo.saf.fixe.epsi, width=8cm}\end{figure}

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